{"version":"1.0.0","segments":[{"startTime":0.19,"endTime":3.07,"body":"- Good evening, everybody,"},{"startTime":0.19,"endTime":3.07,"body":"and happy new year"},{"startTime":3.07,"endTime":6.8,"body":"to everyone gathered in"},{"startTime":3.07,"endTime":6.8,"body":"this lecture theater."},{"startTime":6.8,"endTime":10.07,"body":"I'd like to welcome you to lecture three"},{"startTime":10.07,"endTime":13.9,"body":"in our series on Cosmic Revolutions."},{"startTime":13.9,"endTime":16.34,"body":"And the title of tonight's lecture"},{"startTime":16.34,"endTime":19.99,"body":"is Structures in the Universe."},{"startTime":19.99,"endTime":24.7,"body":"Our universe is a richly structured place."},{"startTime":24.7,"endTime":28.07,"body":"Now that may not seem a"},{"startTime":24.7,"endTime":28.07,"body":"surprising statement to make"},{"startTime":28.07,"endTime":29.64,"body":"on the face of it."},{"startTime":29.64,"endTime":33.4,"body":"After all, we know quite"},{"startTime":29.64,"endTime":33.4,"body":"a lot from our night sky,"},{"startTime":33.4,"endTime":36.42,"body":"we know about the stars in the foreground,"},{"startTime":36.42,"endTime":39.94,"body":"in the near field from our own galaxy."},{"startTime":39.94,"endTime":42.32,"body":"And we see patterns in those."},{"startTime":42.32,"endTime":44.55,"body":"And we see galaxies beyond,"},{"startTime":44.55,"endTime":49.55,"body":"and even more exciting patterns"},{"startTime":44.55,"endTime":49.55,"body":"of galaxies beyond that."},{"startTime":50.38,"endTime":54.31,"body":"So the idea that"},{"startTime":50.38,"endTime":54.31,"body":"structures in the universe"},{"startTime":54.31,"endTime":58.0,"body":"are a thing isn't surprising,"},{"startTime":58.0,"endTime":61.25,"body":"and it won't come as something new to us."},{"startTime":61.25,"endTime":63.93,"body":"I'm showing a projection"},{"startTime":61.25,"endTime":63.93,"body":"of some of the things"},{"startTime":63.93,"endTime":66.9,"body":"that we can see in the night sky"},{"startTime":66.9,"endTime":70.16,"body":"in what are called galactic coordinates."},{"startTime":70.16,"endTime":74.35,"body":"The plane of our galaxy"},{"startTime":70.16,"endTime":74.35,"body":"is shown along the center"},{"startTime":74.35,"endTime":76.863,"body":"of the image that you can see here."},{"startTime":78.13,"endTime":80.78,"body":"On exactly the same projection,"},{"startTime":80.78,"endTime":85.41,"body":"I'm going to show you what the"},{"startTime":80.78,"endTime":85.41,"body":"cosmic microwave background"},{"startTime":85.41,"endTime":89.46,"body":"looks like, which I described"},{"startTime":85.41,"endTime":89.46,"body":"in quite a bit of detail"},{"startTime":89.46,"endTime":94.45,"body":"in the first lecture in this"},{"startTime":89.46,"endTime":94.45,"body":"series on Cosmic Revolutions."},{"startTime":94.45,"endTime":97.78,"body":"That was the lecture"},{"startTime":94.45,"endTime":97.78,"body":"called Early Universe."},{"startTime":97.78,"endTime":100.89,"body":"So what I want you to appreciate"},{"startTime":100.89,"endTime":104.72,"body":"is that this is how the universe was,"},{"startTime":104.72,"endTime":108.02,"body":"and this is how the universe is."},{"startTime":108.02,"endTime":112.72,"body":"At least as far as an observer"},{"startTime":108.02,"endTime":112.72,"body":"on Earth is concerned."},{"startTime":112.72,"endTime":117.72,"body":"The projection is exactly the"},{"startTime":112.72,"endTime":117.72,"body":"same in a coordinate sense,"},{"startTime":118.94,"endTime":123.56,"body":"but in this image, looking"},{"startTime":118.94,"endTime":123.56,"body":"much, much further back in time,"},{"startTime":123.56,"endTime":127.51,"body":"nearly 14 billion years back in time,"},{"startTime":127.51,"endTime":132.39,"body":"the universe was a much more smooth place."},{"startTime":132.39,"endTime":135.52,"body":"It was a much more homogenous place."},{"startTime":135.52,"endTime":140.52,"body":"The differences across this"},{"startTime":135.52,"endTime":140.52,"body":"image are very, very subtle."},{"startTime":142.08,"endTime":143.89,"body":"The temperature scale at the bottom,"},{"startTime":143.89,"endTime":148.61,"body":"temperature being how we"},{"startTime":143.89,"endTime":148.61,"body":"represent the differences"},{"startTime":148.61,"endTime":151.98,"body":"in the physical properties in the universe"},{"startTime":151.98,"endTime":156.98,"body":"at these early times, that I"},{"startTime":151.98,"endTime":156.98,"body":"described two lectures ago,"},{"startTime":157.64,"endTime":159.7,"body":"are very subtle indeed."},{"startTime":159.7,"endTime":163.68,"body":"On the left-hand side, the extreme minimum"},{"startTime":163.68,"endTime":168.68,"body":"is minus 300 micro degrees Kelvin."},{"startTime":169.63,"endTime":174.55,"body":"And on the right-hand side,"},{"startTime":169.63,"endTime":174.55,"body":"plus 300 micro degrees."},{"startTime":174.55,"endTime":178.51,"body":"So very, very subtle variations indeed."},{"startTime":178.51,"endTime":180.22,"body":"If we could have a swimming pool"},{"startTime":180.22,"endTime":183.73,"body":"that was as smooth as"},{"startTime":180.22,"endTime":183.73,"body":"the universe used to be,"},{"startTime":183.73,"endTime":187.363,"body":"it would be very, very flat indeed."},{"startTime":188.91,"endTime":192.72,"body":"To be comparably smooth,"},{"startTime":188.91,"endTime":192.72,"body":"the largest ripples"},{"startTime":192.72,"endTime":195.83,"body":"on a swimming pool of"},{"startTime":192.72,"endTime":195.83,"body":"average depth of a few meters"},{"startTime":196.7,"endTime":201.7,"body":"would be less than 1/100"},{"startTime":196.7,"endTime":201.7,"body":"of one millimeter high."},{"startTime":202.4,"endTime":206.87,"body":"That's how smooth the universe used to be."},{"startTime":206.87,"endTime":211.05,"body":"So against that backdrop in that context,"},{"startTime":211.05,"endTime":214.673,"body":"the fact that the universe"},{"startTime":211.05,"endTime":214.673,"body":"is highly structured now,"},{"startTime":215.55,"endTime":218.5,"body":"perhaps is a little bit surprising."},{"startTime":218.5,"endTime":221.7,"body":"After all, the universe used to be"},{"startTime":221.7,"endTime":224.1,"body":"a much more homogenous place,"},{"startTime":224.1,"endTime":229.1,"body":"but now whenever and wherever"},{"startTime":224.1,"endTime":229.1,"body":"we look in the night sky,"},{"startTime":229.15,"endTime":232.59,"body":"you would not use the adjective smooth."},{"startTime":232.59,"endTime":236.77,"body":"You might use the adjective"},{"startTime":232.59,"endTime":236.77,"body":"lumpy or structured."},{"startTime":236.77,"endTime":239.45,"body":"Here's a view of the night sky"},{"startTime":239.45,"endTime":242.52,"body":"in the constellation of Carina."},{"startTime":242.52,"endTime":245.66,"body":"You can see a little bit"},{"startTime":242.52,"endTime":245.66,"body":"of a cluster of stars"},{"startTime":245.66,"endTime":249.96,"body":"over here on the right,"},{"startTime":245.66,"endTime":249.96,"body":"and a little bit of Nebula,"},{"startTime":249.96,"endTime":254.6,"body":"nebulosity gas in the top left."},{"startTime":254.6,"endTime":256.34,"body":"This was an image taken"},{"startTime":256.34,"endTime":259.333,"body":"with one of my Global Jet Watch cameras."},{"startTime":260.45,"endTime":263.23,"body":"So that's looking at"},{"startTime":260.45,"endTime":263.23,"body":"stars within our galaxy."},{"startTime":263.23,"endTime":265.25,"body":"They are pretty lumpy,"},{"startTime":265.25,"endTime":269.08,"body":"but when we start to look"},{"startTime":265.25,"endTime":269.08,"body":"beyond our own galaxy,"},{"startTime":269.08,"endTime":273.14,"body":"ideally with the assistance"},{"startTime":269.08,"endTime":273.14,"body":"of a space telescope,"},{"startTime":273.14,"endTime":276.55,"body":"then there is no doubt whatsoever"},{"startTime":276.55,"endTime":281.55,"body":"that the universe now is a"},{"startTime":276.55,"endTime":281.55,"body":"very inhomogeneous place."},{"startTime":282.34,"endTime":286.82,"body":"Matter is very unevenly distributed."},{"startTime":286.82,"endTime":291.82,"body":"There are all these lumps of"},{"startTime":286.82,"endTime":291.82,"body":"matter, known as galaxies,"},{"startTime":291.89,"endTime":294.783,"body":"and in-between not so much matter."},{"startTime":295.96,"endTime":300.323,"body":"The universe now is a"},{"startTime":295.96,"endTime":300.323,"body":"very inhomogeneous place."},{"startTime":301.16,"endTime":302.9,"body":"So how on earth did we get"},{"startTime":302.9,"endTime":306.32,"body":"from that amazingly"},{"startTime":302.9,"endTime":306.32,"body":"smooth state of affairs"},{"startTime":306.32,"endTime":310.87,"body":"to this amazingly"},{"startTime":306.32,"endTime":310.87,"body":"inhomogeneous state of affairs"},{"startTime":310.87,"endTime":314.35,"body":"where there are all sorts"},{"startTime":310.87,"endTime":314.35,"body":"of different galaxies"},{"startTime":314.35,"endTime":318.01,"body":"throughout the observable universe?"},{"startTime":318.01,"endTime":320.81,"body":"Where did these structures come from?"},{"startTime":320.81,"endTime":325.58,"body":"How did we transition from"},{"startTime":320.81,"endTime":325.58,"body":"the smooth homogenous state"},{"startTime":325.58,"endTime":329.28,"body":"to the very lumpy inhomogeneous state"},{"startTime":329.28,"endTime":331.573,"body":"with the structures that we see today?"},{"startTime":332.72,"endTime":334.78,"body":"Well, I want to begin by just touching"},{"startTime":334.78,"endTime":338.113,"body":"on how one star forms."},{"startTime":339.13,"endTime":344.13,"body":"If you have a lot of gas,"},{"startTime":339.13,"endTime":344.13,"body":"and if it's not too hot,"},{"startTime":344.55,"endTime":347.03,"body":"and if there's enough of it,"},{"startTime":347.03,"endTime":349.6,"body":"so there is quite a lot of mass,"},{"startTime":349.6,"endTime":352.8,"body":"then you have the necessary ingredients"},{"startTime":352.8,"endTime":354.673,"body":"to be able to form a star."},{"startTime":355.99,"endTime":359.53,"body":"Large masses of gas are involved,"},{"startTime":359.53,"endTime":361.16,"body":"and let me remind you at this point"},{"startTime":361.16,"endTime":365.32,"body":"what the mass of our"},{"startTime":361.16,"endTime":365.32,"body":"nearest star is, the sun,"},{"startTime":365.32,"endTime":370.32,"body":"the massive, our sun, is two"},{"startTime":365.32,"endTime":370.32,"body":"times 10 to the power of 30,"},{"startTime":371.57,"endTime":374.33,"body":"three zero kilograms."},{"startTime":374.33,"endTime":377.973,"body":"So you have to have a lot of mass."},{"startTime":378.9,"endTime":380.5,"body":"And if you have got a lot of mass,"},{"startTime":380.5,"endTime":383.0,"body":"and, you know, we've got"},{"startTime":380.5,"endTime":383.0,"body":"the whole universe here,"},{"startTime":383.0,"endTime":387.3,"body":"then you can hope to form a star from it."},{"startTime":387.3,"endTime":390.93,"body":"So let's imagine we've"},{"startTime":387.3,"endTime":390.93,"body":"got lots of primordial gas"},{"startTime":390.93,"endTime":395.93,"body":"and there are inhomogeneities,"},{"startTime":390.93,"endTime":395.93,"body":"lumpiness, unevenness"},{"startTime":396.41,"endTime":400.223,"body":"in the distribution of"},{"startTime":396.41,"endTime":400.223,"body":"that primordial gas."},{"startTime":401.3,"endTime":405.0,"body":"And now you think about the"},{"startTime":401.3,"endTime":405.0,"body":"temperature of that gas."},{"startTime":405.0,"endTime":407.91,"body":"What does it mean for gas to be hot?"},{"startTime":407.91,"endTime":410.16,"body":"When you've got gas that's hot,"},{"startTime":410.16,"endTime":413.2,"body":"it means the atoms or"},{"startTime":410.16,"endTime":413.2,"body":"perhaps the molecules"},{"startTime":413.2,"endTime":417.42,"body":"within that gas cloud are"},{"startTime":413.2,"endTime":417.42,"body":"whizzing around at great speed."},{"startTime":417.42,"endTime":419.72,"body":"That's what it means for a gas cloud"},{"startTime":419.72,"endTime":422.03,"body":"to have a high temperature."},{"startTime":422.03,"endTime":426.0,"body":"A gas cloud at low temperature"},{"startTime":422.03,"endTime":426.0,"body":"would have the atoms"},{"startTime":426.0,"endTime":429.28,"body":"moving around at a much"},{"startTime":426.0,"endTime":429.28,"body":"more leisurely pace."},{"startTime":429.28,"endTime":432.54,"body":"Those atoms have less thermal energy"},{"startTime":432.54,"endTime":436.44,"body":"and hence less kinetic energy."},{"startTime":436.44,"endTime":440.58,"body":"So if you've got a big"},{"startTime":436.44,"endTime":440.58,"body":"mass of primordial gas"},{"startTime":440.58,"endTime":445.58,"body":"and it's not too hot, then"},{"startTime":440.58,"endTime":445.58,"body":"a competition can begin."},{"startTime":447.47,"endTime":451.59,"body":"There's a process which"},{"startTime":447.47,"endTime":451.59,"body":"we call Jeans collapse,"},{"startTime":451.59,"endTime":456.56,"body":"which describes the competition"},{"startTime":451.59,"endTime":456.56,"body":"between the pull of gravity"},{"startTime":456.56,"endTime":460.32,"body":"that the center of mass of that gas cloud"},{"startTime":460.32,"endTime":463.65,"body":"will experience as it"},{"startTime":460.32,"endTime":463.65,"body":"gravitationally attracts"},{"startTime":463.65,"endTime":465.723,"body":"all the other mass around it,"},{"startTime":466.79,"endTime":470.69,"body":"versus the thermal kinetic"},{"startTime":466.79,"endTime":470.69,"body":"energy of the atoms"},{"startTime":470.69,"endTime":474.78,"body":"wanting to whiz around and do"},{"startTime":470.69,"endTime":474.78,"body":"their own random exploration"},{"startTime":474.78,"endTime":478.19,"body":"of space without being drawn in"},{"startTime":478.19,"endTime":482.15,"body":"under gravity to collapse into something"},{"startTime":482.15,"endTime":484.453,"body":"they can't necessarily escape from."},{"startTime":485.81,"endTime":490.81,"body":"If you have a gas cloud"},{"startTime":485.81,"endTime":490.81,"body":"that is cold and is dense,"},{"startTime":491.04,"endTime":493.99,"body":"that is favorable to collapse,"},{"startTime":493.99,"endTime":498.103,"body":"gravity will win out over"},{"startTime":493.99,"endTime":498.103,"body":"all that thermal energy."},{"startTime":499.81,"endTime":504.81,"body":"When the gas starts to coalesce"},{"startTime":499.81,"endTime":504.81,"body":"and become denser still,"},{"startTime":504.89,"endTime":507.81,"body":"as long as it's sufficiently dense,"},{"startTime":507.81,"endTime":511.6,"body":"then gravitational"},{"startTime":507.81,"endTime":511.6,"body":"collapse is inescapable,"},{"startTime":511.6,"endTime":514.26,"body":"but then something different happens."},{"startTime":514.26,"endTime":517.38,"body":"The gas becomes very, very, extremely hot"},{"startTime":517.38,"endTime":521.34,"body":"and a process that I talked"},{"startTime":517.38,"endTime":521.34,"body":"about in my second lecture"},{"startTime":521.34,"endTime":524.7,"body":"in this series on Cosmic Revolutions,"},{"startTime":524.7,"endTime":529.7,"body":"entitled Atomic Universe"},{"startTime":524.7,"endTime":529.7,"body":"about a process called fusion."},{"startTime":530.17,"endTime":533.4,"body":"That process of fusion then takes place."},{"startTime":533.4,"endTime":538.37,"body":"If you've got a massive gas,"},{"startTime":533.4,"endTime":538.37,"body":"where fusion has been ignited,"},{"startTime":538.37,"endTime":541.893,"body":"because the temperatures are"},{"startTime":538.37,"endTime":541.893,"body":"so high, you have got a star."},{"startTime":542.83,"endTime":547.083,"body":"That, in a nutshell, is how stars form."},{"startTime":548.21,"endTime":553.21,"body":"So stars clearly do form"},{"startTime":548.21,"endTime":553.21,"body":"all across the galaxy,"},{"startTime":554.03,"endTime":557.34,"body":"all across the universe, but in reality,"},{"startTime":557.34,"endTime":562.16,"body":"they don't tend to form"},{"startTime":557.34,"endTime":562.16,"body":"as isolated systems."},{"startTime":562.16,"endTime":565.65,"body":"Typically, most of the star formation"},{"startTime":565.65,"endTime":570.3,"body":"that we see in our galaxy"},{"startTime":565.65,"endTime":570.3,"body":"today, or in other galaxies,"},{"startTime":570.3,"endTime":571.85,"body":"is in the context"},{"startTime":571.85,"endTime":575.27,"body":"of what are sometimes"},{"startTime":571.85,"endTime":575.27,"body":"called stellar nurseries,"},{"startTime":575.27,"endTime":578.193,"body":"regions of ongoing star formation."},{"startTime":579.31,"endTime":582.9,"body":"This will, I'm sure,"},{"startTime":579.31,"endTime":582.9,"body":"be a very familiar view"},{"startTime":582.9,"endTime":586.22,"body":"in the night sky, at least for those of us"},{"startTime":586.22,"endTime":589.14,"body":"who haven't had the cloudy"},{"startTime":586.22,"endTime":589.14,"body":"weather that we've been having"},{"startTime":589.14,"endTime":591.85,"body":"in the UK in the past few months."},{"startTime":591.85,"endTime":594.33,"body":"This is, of course, Orion."},{"startTime":594.33,"endTime":599.33,"body":"And I want us to just zoom in"},{"startTime":594.33,"endTime":599.33,"body":"on the central bright region"},{"startTime":601.23,"endTime":604.1,"body":"in the sword of Orion."},{"startTime":604.1,"endTime":606.96,"body":"You can actually see with the naked eye"},{"startTime":606.96,"endTime":611.67,"body":"that that object is a bit"},{"startTime":606.96,"endTime":611.67,"body":"fuzzy and not very star-like."},{"startTime":611.67,"endTime":613.75,"body":"If you zoom in with a telescope,"},{"startTime":613.75,"endTime":616.93,"body":"and I used my telescope in India"},{"startTime":616.93,"endTime":619.38,"body":"that's part of the"},{"startTime":616.93,"endTime":619.38,"body":"Global Jet Watch network,"},{"startTime":619.38,"endTime":623.153,"body":"then you see, of course,"},{"startTime":619.38,"endTime":623.153,"body":"the famous Orion Nebula."},{"startTime":624.49,"endTime":627.54,"body":"This, in fact, is the closest region"},{"startTime":627.54,"endTime":632.54,"body":"of massive star formation"},{"startTime":627.54,"endTime":632.54,"body":"to our own solar system."},{"startTime":632.9,"endTime":634.91,"body":"The very brightest region there,"},{"startTime":634.91,"endTime":637.63,"body":"not really resolved in"},{"startTime":634.91,"endTime":637.63,"body":"this particular image,"},{"startTime":637.63,"endTime":641.41,"body":"is the trapezium set of stars."},{"startTime":641.41,"endTime":646.41,"body":"It's a very young cluster"},{"startTime":641.41,"endTime":646.41,"body":"of stars, very, very young,"},{"startTime":646.55,"endTime":651.55,"body":"very, very hot and irradiating"},{"startTime":646.55,"endTime":651.55,"body":"all the gas around it"},{"startTime":652.34,"endTime":657.34,"body":"that has yet to collapse"},{"startTime":652.34,"endTime":657.34,"body":"under gravity and form stars."},{"startTime":657.84,"endTime":660.74,"body":"Indeed, the presence of those bright stars"},{"startTime":660.74,"endTime":664.54,"body":"right in that central trapezium region"},{"startTime":664.54,"endTime":667.74,"body":"is offsetting the other gas around it,"},{"startTime":667.74,"endTime":672.3,"body":"collapsing under gravity,"},{"startTime":667.74,"endTime":672.3,"body":"because it's heating up that gas,"},{"startTime":672.3,"endTime":675.75,"body":"and its helping it in the fight"},{"startTime":675.75,"endTime":679.53,"body":"of gravitational attraction"},{"startTime":675.75,"endTime":679.53,"body":"causing collapse,"},{"startTime":679.53,"endTime":683.433,"body":"and thermal energy, which"},{"startTime":679.53,"endTime":683.433,"body":"preserves the gaseous state."},{"startTime":684.83,"endTime":689.83,"body":"So stellar nurseries are"},{"startTime":684.83,"endTime":689.83,"body":"regions of high activity."},{"startTime":690.31,"endTime":693.68,"body":"Stars form, they can"},{"startTime":690.31,"endTime":693.68,"body":"stop other stars forming."},{"startTime":693.68,"endTime":697.8,"body":"It really depends on"},{"startTime":693.68,"endTime":697.8,"body":"how dense the region is"},{"startTime":697.8,"endTime":700.313,"body":"and how massive some of the stars are."},{"startTime":701.71,"endTime":706.71,"body":"But if you do get an entire"},{"startTime":701.71,"endTime":706.71,"body":"group of stars forming together,"},{"startTime":707.05,"endTime":710.22,"body":"and it can be larger than"},{"startTime":707.05,"endTime":710.22,"body":"just the very small number"},{"startTime":710.22,"endTime":713.62,"body":"in the Orion Nebula that I just mentioned,"},{"startTime":713.62,"endTime":718.1,"body":"you can get something that"},{"startTime":713.62,"endTime":718.1,"body":"is akin to a mini-galaxy"},{"startTime":718.1,"endTime":720.343,"body":"within our own galaxy."},{"startTime":721.78,"endTime":724.883,"body":"You can get a cluster of stars."},{"startTime":725.92,"endTime":729.15,"body":"So there are predominantly"},{"startTime":725.92,"endTime":729.15,"body":"two different types"},{"startTime":729.15,"endTime":734.15,"body":"of clusters of stars in"},{"startTime":729.15,"endTime":734.15,"body":"our galaxy, the Milky Way."},{"startTime":734.3,"endTime":738.55,"body":"Globular clusters and open clusters."},{"startTime":738.55,"endTime":742.17,"body":"I'm going to talk about the"},{"startTime":738.55,"endTime":742.17,"body":"globular clusters to start with."},{"startTime":742.17,"endTime":744.26,"body":"These are pretty remarkable."},{"startTime":744.26,"endTime":748.66,"body":"They have a lot of stars and"},{"startTime":744.26,"endTime":748.66,"body":"a lot here is a million or so,"},{"startTime":748.66,"endTime":751.16,"body":"some large number like a million."},{"startTime":751.16,"endTime":755.7,"body":"You got a lot of stars,"},{"startTime":751.16,"endTime":755.7,"body":"very similar in age,"},{"startTime":755.7,"endTime":760.143,"body":"meaning they all formed"},{"startTime":755.7,"endTime":760.143,"body":"around the same time."},{"startTime":761.62,"endTime":763.49,"body":"If you've got a lot of stars all forming"},{"startTime":763.49,"endTime":766.7,"body":"around the same time,"},{"startTime":763.49,"endTime":766.7,"body":"they're not all going to be,"},{"startTime":766.7,"endTime":769.86,"body":"even though they're born in"},{"startTime":766.7,"endTime":769.86,"body":"the same litter, as it were,"},{"startTime":769.86,"endTime":774.86,"body":"in no sense are they identical"},{"startTime":769.86,"endTime":774.86,"body":"siblings, far from it."},{"startTime":775.3,"endTime":777.743,"body":"If their masses are different,"},{"startTime":778.89,"endTime":781.69,"body":"the more massive ones"},{"startTime":778.89,"endTime":781.69,"body":"will evolve more quickly,"},{"startTime":781.69,"endTime":785.22,"body":"the less massive ones"},{"startTime":781.69,"endTime":785.22,"body":"will evolve more slowly."},{"startTime":785.22,"endTime":789.06,"body":"And so it's a very interesting laboratory"},{"startTime":789.06,"endTime":791.84,"body":"to be able to study stellar evolution"},{"startTime":791.84,"endTime":796.02,"body":"from the same assumed starting point."},{"startTime":796.02,"endTime":797.993,"body":"And that's really quite important."},{"startTime":799.07,"endTime":802.06,"body":"Something else that is a"},{"startTime":799.07,"endTime":802.06,"body":"feature of globular clusters"},{"startTime":802.06,"endTime":805.66,"body":"is that because of the"},{"startTime":802.06,"endTime":805.66,"body":"most massive stars within"},{"startTime":805.66,"endTime":807.53,"body":"will evolve most quickly,"},{"startTime":807.53,"endTime":812.36,"body":"and potentially explode in a supernova,"},{"startTime":812.36,"endTime":817.36,"body":"that blast wave, that shockwave"},{"startTime":812.36,"endTime":817.36,"body":"from the supernova explosion"},{"startTime":817.62,"endTime":820.86,"body":"will do something else"},{"startTime":817.62,"endTime":820.86,"body":"to any residual gas,"},{"startTime":820.86,"endTime":823.99,"body":"which hasn't quite collapsed into stars."},{"startTime":823.99,"endTime":828.99,"body":"It'll sweep it out the way, it"},{"startTime":823.99,"endTime":828.99,"body":"will clear out any other gas."},{"startTime":829.15,"endTime":833.5,"body":"And so you can get a"},{"startTime":829.15,"endTime":833.5,"body":"very unusual environment"},{"startTime":833.5,"endTime":835.86,"body":"within a globular clusters."},{"startTime":835.86,"endTime":839.09,"body":"Just a big bunch of"},{"startTime":835.86,"endTime":839.09,"body":"stars, self gravitating,"},{"startTime":839.09,"endTime":841.26,"body":"'cause they're all pretty close together,"},{"startTime":841.26,"endTime":846.163,"body":"all formed out of the same"},{"startTime":841.26,"endTime":846.163,"body":"massive primordial gas cloud,"},{"startTime":847.5,"endTime":851.67,"body":"but free of gas that"},{"startTime":847.5,"endTime":851.67,"body":"could form any other stars"},{"startTime":851.67,"endTime":852.84,"body":"in the future."},{"startTime":852.84,"endTime":855.7,"body":"So quite a remarkable environment,"},{"startTime":855.7,"endTime":859.14,"body":"if you've had a sufficiently"},{"startTime":855.7,"endTime":859.14,"body":"massive star at the center"},{"startTime":859.14,"endTime":862.81,"body":"that it has evolved"},{"startTime":859.14,"endTime":862.81,"body":"quickly and gone supernova."},{"startTime":862.81,"endTime":864.72,"body":"If you have that, it will put a stop"},{"startTime":864.72,"endTime":866.48,"body":"to any further star formation,"},{"startTime":866.48,"endTime":871.48,"body":"because it will have wiped"},{"startTime":866.48,"endTime":871.48,"body":"out any residual gas,"},{"startTime":871.6,"endTime":876.0,"body":"but gravity will continue"},{"startTime":871.6,"endTime":876.0,"body":"to be highly relevant"},{"startTime":876.0,"endTime":878.35,"body":"to that cluster of galaxies,"},{"startTime":878.35,"endTime":881.58,"body":"regardless of the presence or the absence"},{"startTime":881.58,"endTime":886.55,"body":"of any residual gas that"},{"startTime":881.58,"endTime":886.55,"body":"never made it into stars."},{"startTime":886.55,"endTime":890.67,"body":"And so we do see these"},{"startTime":886.55,"endTime":890.67,"body":"really beautiful structures"},{"startTime":890.67,"endTime":894.41,"body":"throughout our galaxy, not"},{"startTime":890.67,"endTime":894.41,"body":"just in the disc of our galaxy,"},{"startTime":894.41,"endTime":898.2,"body":"but throughout its halo,"},{"startTime":894.41,"endTime":898.2,"body":"these mini-galaxies,"},{"startTime":898.2,"endTime":900.783,"body":"these galaxies within our galaxy."},{"startTime":901.75,"endTime":905.94,"body":"So what we're seeing on the"},{"startTime":901.75,"endTime":905.94,"body":"screen here is Messier 22,"},{"startTime":905.94,"endTime":909.32,"body":"a globular cluster in Sagittarius."},{"startTime":909.32,"endTime":914.32,"body":"It's about 11,000 light years"},{"startTime":909.32,"endTime":914.32,"body":"away from the solar system."},{"startTime":915.21,"endTime":920.21,"body":"It's one of over 150"},{"startTime":915.21,"endTime":920.21,"body":"globulars inside our galaxy."},{"startTime":921.89,"endTime":924.26,"body":"So there aren't a huge number of them,"},{"startTime":924.26,"endTime":925.88,"body":"but there are enough of them"},{"startTime":925.88,"endTime":929.55,"body":"for it to be really remarkably"},{"startTime":925.88,"endTime":929.55,"body":"interesting to study them."},{"startTime":929.55,"endTime":934.25,"body":"They can be very old, because"},{"startTime":929.55,"endTime":934.25,"body":"they're really very stable,"},{"startTime":934.25,"endTime":938.73,"body":"once they've formed, because"},{"startTime":934.25,"endTime":938.73,"body":"they're quite tightly bound"},{"startTime":938.73,"endTime":941.0,"body":"under their own gravity,"},{"startTime":941.0,"endTime":943.81,"body":"they're pretty resilient to anything else"},{"startTime":943.81,"endTime":946.82,"body":"that they happen to sort of rock up past"},{"startTime":946.82,"endTime":950.373,"body":"as they orbit throughout our galaxy."},{"startTime":951.24,"endTime":953.233,"body":"They're really remarkably stable."},{"startTime":954.16,"endTime":957.26,"body":"This is a picture of Omega Cen"},{"startTime":957.26,"endTime":960.12,"body":"in the Centaurus constellation, of course,"},{"startTime":960.12,"endTime":964.44,"body":"taken by my colleague on the"},{"startTime":960.12,"endTime":964.44,"body":"Global Jet Watch, Steven Lee."},{"startTime":964.44,"endTime":969.44,"body":"This was discovered in"},{"startTime":964.44,"endTime":969.44,"body":"1677 by Edmund Halley,"},{"startTime":970.6,"endTime":973.63,"body":"but, of course, with the"},{"startTime":970.6,"endTime":973.63,"body":"superior optics of today,"},{"startTime":973.63,"endTime":975.94,"body":"I'm sure you could get a"},{"startTime":973.63,"endTime":975.94,"body":"pretty good photo of this"},{"startTime":975.94,"endTime":977.62,"body":"just with a smartphone,"},{"startTime":977.62,"endTime":980.71,"body":"not quite as good as the one"},{"startTime":977.62,"endTime":980.71,"body":"I'm showing you, of course,"},{"startTime":980.71,"endTime":984.71,"body":"but certainly a sense that"},{"startTime":980.71,"endTime":984.71,"body":"it's a resolved collection"},{"startTime":984.71,"endTime":988.1,"body":"of stars and not at all something"},{"startTime":988.1,"endTime":991.093,"body":"that you could ever confuse with a star."},{"startTime":992.27,"endTime":994.45,"body":"From one side to the other,"},{"startTime":994.45,"endTime":997.35,"body":"depending on exactly where you define it,"},{"startTime":997.35,"endTime":1002.35,"body":"it's something like 150 light years across"},{"startTime":1003.12,"endTime":1005.28,"body":"from one side to the other."},{"startTime":1005.28,"endTime":1008.343,"body":"From the solar system,"},{"startTime":1005.28,"endTime":1008.343,"body":"that's quite a long way,"},{"startTime":1008.343,"endTime":1012.69,"body":"17,000 light years."},{"startTime":1012.69,"endTime":1016.82,"body":"This particular globular"},{"startTime":1012.69,"endTime":1016.82,"body":"cluster is a big one."},{"startTime":1016.82,"endTime":1019.81,"body":"It's the largest one in our galaxy."},{"startTime":1019.81,"endTime":1024.81,"body":"It contains about 10 million"},{"startTime":1019.81,"endTime":1024.81,"body":"stars, beautifully pristine,"},{"startTime":1025.92,"endTime":1030.92,"body":"almost spherically symmetric, free of gas,"},{"startTime":1031.4,"endTime":1036.163,"body":"and a fascinating object"},{"startTime":1031.4,"endTime":1036.163,"body":"to study in its own right."},{"startTime":1037.55,"endTime":1040.22,"body":"This is a rather more weedy version."},{"startTime":1040.22,"endTime":1042.56,"body":"In fact, this one isn't"},{"startTime":1040.22,"endTime":1042.56,"body":"really a globular cluster."},{"startTime":1042.56,"endTime":1046.2,"body":"Although it's quite compact,"},{"startTime":1046.2,"endTime":1048.23,"body":"as clusters of stars can go."},{"startTime":1048.23,"endTime":1052.51,"body":"This one actually counts"},{"startTime":1048.23,"endTime":1052.51,"body":"as an open cluster."},{"startTime":1052.51,"endTime":1056.94,"body":"There's less than, or"},{"startTime":1052.51,"endTime":1056.94,"body":"fewer than 1,000 stars"},{"startTime":1056.94,"endTime":1059.11,"body":"in this particular open cluster."},{"startTime":1059.11,"endTime":1063.52,"body":"And an open cluster is much"},{"startTime":1059.11,"endTime":1063.52,"body":"more sparsely populated."},{"startTime":1063.52,"endTime":1066.04,"body":"It's much less, the stars within it"},{"startTime":1066.04,"endTime":1069.65,"body":"are much less strongly bound."},{"startTime":1069.65,"endTime":1072.06,"body":"And that means they're much less resilient"},{"startTime":1072.06,"endTime":1076.15,"body":"to any other gravitational inhomogeneity"},{"startTime":1076.15,"endTime":1078.3,"body":"that they might orbit past"},{"startTime":1078.3,"endTime":1082.72,"body":"as they precess through our galaxy."},{"startTime":1082.72,"endTime":1087.47,"body":"So you don't tend to see"},{"startTime":1082.72,"endTime":1087.47,"body":"very old open clusters"},{"startTime":1087.47,"endTime":1089.2,"body":"because they're not resilient."},{"startTime":1089.2,"endTime":1093.563,"body":"They're not stable against"},{"startTime":1089.2,"endTime":1093.563,"body":"gravitational perturbation."},{"startTime":1094.6,"endTime":1096.5,"body":"They're still beautiful, though."},{"startTime":1096.5,"endTime":1097.54,"body":"Here is another one."},{"startTime":1097.54,"endTime":1102.54,"body":"This is NGC 6250 shown on the left there."},{"startTime":1103.45,"endTime":1108.45,"body":"Fewer stars, indeed,"},{"startTime":1103.45,"endTime":1108.45,"body":"and next to Barnard 86,"},{"startTime":1108.71,"endTime":1112.36,"body":"which is a dark Nebula where"},{"startTime":1108.71,"endTime":1112.36,"body":"it's basically blotting out,"},{"startTime":1112.36,"endTime":1116.31,"body":"absorbing all the light behind it."},{"startTime":1116.31,"endTime":1120.963,"body":"So open clusters can still"},{"startTime":1116.31,"endTime":1120.963,"body":"be very interesting to study,"},{"startTime":1122.12,"endTime":1124.95,"body":"but they're different,"},{"startTime":1122.12,"endTime":1124.95,"body":"they're much more fragile"},{"startTime":1124.95,"endTime":1126.903,"body":"than the globular clusters."},{"startTime":1128.36,"endTime":1131.95,"body":"So let's now go up a scale,"},{"startTime":1131.95,"endTime":1134.27,"body":"and let's start to think about galaxies,"},{"startTime":1134.27,"endTime":1137.93,"body":"and the structures that"},{"startTime":1134.27,"endTime":1137.93,"body":"we see in galaxies."},{"startTime":1137.93,"endTime":1142.19,"body":"So this is a beautiful"},{"startTime":1137.93,"endTime":1142.19,"body":"image of the night sky"},{"startTime":1142.19,"endTime":1144.63,"body":"taken from Australia,"},{"startTime":1144.63,"endTime":1147.16,"body":"and without wishing to be hemispherist,"},{"startTime":1147.16,"endTime":1149.65,"body":"the sky in the Southern hemisphere"},{"startTime":1149.65,"endTime":1153.83,"body":"is superior to the sky in"},{"startTime":1149.65,"endTime":1153.83,"body":"the Northern hemisphere."},{"startTime":1153.83,"endTime":1154.86,"body":"Why do I say that?"},{"startTime":1154.86,"endTime":1157.14,"body":"Well, it's got the center of our galaxy,"},{"startTime":1157.14,"endTime":1159.73,"body":"and that's got a lot"},{"startTime":1157.14,"endTime":1159.73,"body":"of cool stuff going on,"},{"startTime":1159.73,"endTime":1164.26,"body":"but it's also got two galaxies"},{"startTime":1159.73,"endTime":1164.26,"body":"other than the Milky Way,"},{"startTime":1164.26,"endTime":1166.28,"body":"other than our own galaxy,"},{"startTime":1166.28,"endTime":1170.1,"body":"which you can see with the"},{"startTime":1166.28,"endTime":1170.1,"body":"naked eye if it's dark enough."},{"startTime":1170.1,"endTime":1173.393,"body":"These two galaxies indicated"},{"startTime":1170.1,"endTime":1173.393,"body":"by the arrows here."},{"startTime":1174.75,"endTime":1178.16,"body":"So that's obviously the"},{"startTime":1174.75,"endTime":1178.16,"body":"plane of our own galaxy,"},{"startTime":1178.16,"endTime":1179.5,"body":"the Milky Way."},{"startTime":1179.5,"endTime":1180.99,"body":"And these two galaxies are,"},{"startTime":1180.99,"endTime":1185.68,"body":"the lower down one is the"},{"startTime":1180.99,"endTime":1185.68,"body":"so-called Small Magellanic Cloud."},{"startTime":1185.68,"endTime":1190.01,"body":"And this one slightly"},{"startTime":1185.68,"endTime":1190.01,"body":"further up to the right"},{"startTime":1190.01,"endTime":1193.56,"body":"is the Large Magellanic Cloud."},{"startTime":1193.56,"endTime":1196.887,"body":"These are known as satellite"},{"startTime":1193.56,"endTime":1196.887,"body":"galaxies of the Milky Way,"},{"startTime":1196.887,"endTime":1199.8,"body":"and the word satellite is"},{"startTime":1196.887,"endTime":1199.8,"body":"supposed to make us think"},{"startTime":1199.8,"endTime":1202.21,"body":"of things in orbit."},{"startTime":1202.21,"endTime":1205.45,"body":"There's nothing static"},{"startTime":1202.21,"endTime":1205.45,"body":"about these patterns"},{"startTime":1205.45,"endTime":1207.86,"body":"that we see in the night sky,"},{"startTime":1207.86,"endTime":1210.98,"body":"at least as long as you're"},{"startTime":1207.86,"endTime":1210.98,"body":"sufficiently liberated"},{"startTime":1210.98,"endTime":1215.98,"body":"about the timescales on which"},{"startTime":1210.98,"endTime":1215.98,"body":"the night sky is evolving."},{"startTime":1216.53,"endTime":1219.97,"body":"The night sky isn't evolving"},{"startTime":1216.53,"endTime":1219.97,"body":"as far as these kinds of images"},{"startTime":1219.97,"endTime":1223.46,"body":"are concerned on human timescales,"},{"startTime":1223.46,"endTime":1225.403,"body":"but it absolutely is evolving."},{"startTime":1226.55,"endTime":1231.12,"body":"If we go to the other big spiral galaxy"},{"startTime":1231.12,"endTime":1233.33,"body":"in the local group of galaxies,"},{"startTime":1233.33,"endTime":1238.33,"body":"which is a term introduced"},{"startTime":1233.33,"endTime":1238.33,"body":"by Edwin Hubble in 1936"},{"startTime":1239.07,"endTime":1242.25,"body":"for the galaxies that"},{"startTime":1239.07,"endTime":1242.25,"body":"are in our local group"},{"startTime":1242.25,"endTime":1245.32,"body":"and gravitationally"},{"startTime":1242.25,"endTime":1245.32,"body":"interacting with one another,"},{"startTime":1245.32,"endTime":1250.32,"body":"then the most splendid"},{"startTime":1245.32,"endTime":1250.32,"body":"one we see is Messier 31,"},{"startTime":1250.43,"endTime":1252.02,"body":"also known as Andromeda,"},{"startTime":1252.02,"endTime":1255.14,"body":"which as you can see is a"},{"startTime":1252.02,"endTime":1255.14,"body":"really beautiful galaxy."},{"startTime":1255.14,"endTime":1259.54,"body":"You get a sense of its spiral"},{"startTime":1255.14,"endTime":1259.54,"body":"arms from this image here,"},{"startTime":1259.54,"endTime":1262.36,"body":"but in addition to Andromeda itself,"},{"startTime":1262.36,"endTime":1267.36,"body":"it, too, has satellite"},{"startTime":1262.36,"endTime":1267.36,"body":"galaxies orbiting around it."},{"startTime":1267.52,"endTime":1272.52,"body":"And in danger of losing out in"},{"startTime":1267.52,"endTime":1272.52,"body":"the gravitational competition"},{"startTime":1274.71,"endTime":1279.71,"body":"with the main gravitational"},{"startTime":1274.71,"endTime":1279.71,"body":"pull due to the big,"},{"startTime":1280.17,"endTime":1283.633,"body":"the much larger mass that is in Andromeda."},{"startTime":1284.82,"endTime":1289.53,"body":"Satellite galaxies will"},{"startTime":1284.82,"endTime":1289.53,"body":"ultimately get drawn in"},{"startTime":1289.53,"endTime":1293.04,"body":"and they'll orbit through"},{"startTime":1293.04,"endTime":1295.15,"body":"and they won't come out the same way."},{"startTime":1295.15,"endTime":1300.15,"body":"It won't end well for those"},{"startTime":1295.15,"endTime":1300.15,"body":"smaller satellite galaxies"},{"startTime":1300.9,"endTime":1304.21,"body":"that get pulled in by"},{"startTime":1300.9,"endTime":1304.21,"body":"the very big galaxies,"},{"startTime":1304.21,"endTime":1307.17,"body":"be it Andromeda or the Milky Way."},{"startTime":1307.17,"endTime":1312.17,"body":"If I now zoom in to the"},{"startTime":1307.17,"endTime":1312.17,"body":"two satellite galaxies"},{"startTime":1312.31,"endTime":1313.87,"body":"near the Milky Way,"},{"startTime":1313.87,"endTime":1316.37,"body":"this is the Small Magellanic Cloud."},{"startTime":1316.37,"endTime":1318.21,"body":"So called because it was first thought"},{"startTime":1318.21,"endTime":1323.21,"body":"to be some kind of cloud,"},{"startTime":1318.21,"endTime":1323.21,"body":"rather than an external galaxy,"},{"startTime":1323.56,"endTime":1325.77,"body":"a galaxy in its own right."},{"startTime":1325.77,"endTime":1329.41,"body":"And as you can see, no"},{"startTime":1325.77,"endTime":1329.41,"body":"beautiful spiral arms,"},{"startTime":1329.41,"endTime":1333.51,"body":"no pleasing symmetry in its structure."},{"startTime":1333.51,"endTime":1336.07,"body":"It's very much an irregular galaxy."},{"startTime":1336.07,"endTime":1339.75,"body":"It's about four degrees in extent,"},{"startTime":1339.75,"endTime":1343.54,"body":"and it's absolutely undergoing interaction"},{"startTime":1343.54,"endTime":1344.893,"body":"with the Milky Way now."},{"startTime":1345.76,"endTime":1348.58,"body":"It's thought that it was"},{"startTime":1345.76,"endTime":1348.58,"body":"once a spiral galaxy,"},{"startTime":1348.58,"endTime":1350.63,"body":"a fairly small one,"},{"startTime":1350.63,"endTime":1352.83,"body":"but those days are long over"},{"startTime":1352.83,"endTime":1356.4,"body":"due to disruption from"},{"startTime":1352.83,"endTime":1356.4,"body":"gravitational interaction"},{"startTime":1356.4,"endTime":1358.09,"body":"with the Milky Way."},{"startTime":1358.09,"endTime":1362.67,"body":"And this is the Large Magellanic Cloud."},{"startTime":1362.67,"endTime":1365.88,"body":"Something like the stars in this,"},{"startTime":1365.88,"endTime":1370.88,"body":"if you sum up together the"},{"startTime":1365.88,"endTime":1370.88,"body":"masses of all those stars,"},{"startTime":1370.95,"endTime":1371.87,"body":"you get to something"},{"startTime":1371.87,"endTime":1376.57,"body":"like 10 billion times the mass of our sun."},{"startTime":1376.57,"endTime":1378.75,"body":"That's actually only about 1%"},{"startTime":1378.75,"endTime":1381.183,"body":"of the mass of the Milky Way galaxy,"},{"startTime":1382.7,"endTime":1385.69,"body":"and the Milky Way is pulling this"},{"startTime":1385.69,"endTime":1389.43,"body":"towards its gravitational center."},{"startTime":1389.43,"endTime":1393.95,"body":"Collision is inevitable, but"},{"startTime":1389.43,"endTime":1393.95,"body":"it's not on the list of things"},{"startTime":1393.95,"endTime":1396.27,"body":"that we need to worry about right now,"},{"startTime":1396.27,"endTime":1399.46,"body":"because collision is"},{"startTime":1396.27,"endTime":1399.46,"body":"not forecast to happen"},{"startTime":1399.46,"endTime":1403.62,"body":"for another 2.4 billion years."},{"startTime":1403.62,"endTime":1406.163,"body":"That's most definitely a"},{"startTime":1403.62,"endTime":1406.163,"body":"problem for another day."},{"startTime":1407.23,"endTime":1410.15,"body":"But let's get away from"},{"startTime":1407.23,"endTime":1410.15,"body":"the local group of galaxies"},{"startTime":1410.15,"endTime":1414.11,"body":"to bigger, more massive galaxies still."},{"startTime":1414.11,"endTime":1415.18,"body":"So I'm going to talk now"},{"startTime":1415.18,"endTime":1418.14,"body":"about the so-called elliptical galaxies."},{"startTime":1418.14,"endTime":1420.34,"body":"And, of course, that name comes"},{"startTime":1420.34,"endTime":1422.8,"body":"because of the way they look on the sky."},{"startTime":1422.8,"endTime":1425.41,"body":"In projection, when we"},{"startTime":1422.8,"endTime":1425.41,"body":"look through a telescope"},{"startTime":1425.41,"endTime":1429.12,"body":"or with binoculars, they"},{"startTime":1425.41,"endTime":1429.12,"body":"look a bit elongated."},{"startTime":1429.12,"endTime":1430.98,"body":"They look elliptical in projection,"},{"startTime":1430.98,"endTime":1433.72,"body":"but of course they're ellipsoidal,"},{"startTime":1433.72,"endTime":1438.6,"body":"they're very much a 3D"},{"startTime":1433.72,"endTime":1438.6,"body":"object seen in projection"},{"startTime":1438.6,"endTime":1442.33,"body":"on the plane of the night sky."},{"startTime":1442.33,"endTime":1445.987,"body":"These galaxies are parts"},{"startTime":1442.33,"endTime":1445.987,"body":"of the Virgo cluster,"},{"startTime":1445.987,"endTime":1449.95,"body":"M59 on the right and M60"},{"startTime":1451.14,"endTime":1454.04,"body":"is the larger one on the left,"},{"startTime":1454.04,"endTime":1456.173,"body":"just next to a spiral galaxy."},{"startTime":1457.52,"endTime":1462.52,"body":"Yet more galaxies in the"},{"startTime":1457.52,"endTime":1462.52,"body":"Virgo cluster of galaxies."},{"startTime":1462.83,"endTime":1464.68,"body":"So galaxies are all around,"},{"startTime":1464.68,"endTime":1468.77,"body":"and many of them are the"},{"startTime":1464.68,"endTime":1468.77,"body":"beautiful spiral structures"},{"startTime":1469.67,"endTime":1471.8,"body":"that I'll come onto shortly,"},{"startTime":1471.8,"endTime":1473.85,"body":"but the ellipticals are remarkable,"},{"startTime":1473.85,"endTime":1478.12,"body":"because they seem to be very smooth,"},{"startTime":1478.12,"endTime":1480.95,"body":"but smoothness is not all it seems"},{"startTime":1480.95,"endTime":1483.923,"body":"as we'll discover later"},{"startTime":1480.95,"endTime":1483.923,"body":"on in this lecture."},{"startTime":1485.05,"endTime":1487.73,"body":"So perhaps they may seem smooth"},{"startTime":1487.73,"endTime":1490.67,"body":"on the basis of a 12-inch telescope,"},{"startTime":1490.67,"endTime":1494.8,"body":"which is the one used to"},{"startTime":1490.67,"endTime":1494.8,"body":"take this particular image."},{"startTime":1494.8,"endTime":1497.44,"body":"If you want to get a sharper view still"},{"startTime":1497.44,"endTime":1500.77,"body":"of what the distribution of stars is"},{"startTime":1500.77,"endTime":1502.57,"body":"in an elliptical galaxy,"},{"startTime":1502.57,"endTime":1506.32,"body":"then going out to space is a big help."},{"startTime":1506.32,"endTime":1509.01,"body":"So using the Hubble Space Telescope"},{"startTime":1509.01,"endTime":1511.45,"body":"and being way above Earth's atmosphere,"},{"startTime":1511.45,"endTime":1515.67,"body":"this particular elliptical"},{"startTime":1511.45,"endTime":1515.67,"body":"galaxy known as NGC 3610"},{"startTime":1517.46,"endTime":1521.86,"body":"has an amazingly smooth distribution,"},{"startTime":1521.86,"endTime":1525.75,"body":"but it's not uniform throughout"},{"startTime":1521.86,"endTime":1525.75,"body":"its ellipsoidal structure."},{"startTime":1525.75,"endTime":1528.0,"body":"On the contrary, it seems to have a bit"},{"startTime":1528.0,"endTime":1531.52,"body":"of an elongated disc, which"},{"startTime":1528.0,"endTime":1531.52,"body":"would've been quite hard"},{"startTime":1531.52,"endTime":1533.25,"body":"to image from the ground,"},{"startTime":1533.25,"endTime":1535.9,"body":"unless you had a"},{"startTime":1533.25,"endTime":1535.9,"body":"sufficiently large telescope"},{"startTime":1535.9,"endTime":1539.2,"body":"under sufficiently good conditions."},{"startTime":1539.2,"endTime":1543.25,"body":"Most of the bright sources in"},{"startTime":1539.2,"endTime":1543.25,"body":"this sky are actually galaxies"},{"startTime":1543.25,"endTime":1545.62,"body":"apart from the ones with"},{"startTime":1543.25,"endTime":1545.62,"body":"little crosses on them,"},{"startTime":1545.62,"endTime":1547.75,"body":"which are diffraction spikes."},{"startTime":1547.75,"endTime":1551.1,"body":"They are stars, because"},{"startTime":1547.75,"endTime":1551.1,"body":"they appear point-like"},{"startTime":1551.1,"endTime":1553.463,"body":"to the telescope that's observing them."},{"startTime":1554.41,"endTime":1558.0,"body":"So everything around"},{"startTime":1554.41,"endTime":1558.0,"body":"this image, pretty much,"},{"startTime":1558.0,"endTime":1560.98,"body":"apart from a small number"},{"startTime":1558.0,"endTime":1560.98,"body":"of stars is a galaxy,"},{"startTime":1560.98,"endTime":1565.02,"body":"but the focus is on this"},{"startTime":1560.98,"endTime":1565.02,"body":"amazingly smooth one."},{"startTime":1565.02,"endTime":1570.02,"body":"That distribution in brightness"},{"startTime":1565.02,"endTime":1570.02,"body":"profile seems very smooth."},{"startTime":1572.12,"endTime":1576.74,"body":"It's interesting to comment,"},{"startTime":1572.12,"endTime":1576.74,"body":"by the way, on the word galaxy,"},{"startTime":1576.74,"endTime":1581.74,"body":"it came from the Greek word"},{"startTime":1576.74,"endTime":1581.74,"body":"for milk, which is Gala,"},{"startTime":1581.78,"endTime":1584.89,"body":"Gamma, Alpha, Lambda, Alpha."},{"startTime":1584.89,"endTime":1586.8,"body":"Milk, of course, being very smooth"},{"startTime":1586.8,"endTime":1590.9,"body":"and, you know, milk,"},{"startTime":1586.8,"endTime":1590.9,"body":"creamy colored, of course."},{"startTime":1590.9,"endTime":1593.67,"body":"So one can understand"},{"startTime":1590.9,"endTime":1593.67,"body":"where the name came from,"},{"startTime":1593.67,"endTime":1595.23,"body":"for people who didn't have telescopes"},{"startTime":1595.23,"endTime":1596.763,"body":"or smartphones, of course."},{"startTime":1598.43,"endTime":1603.06,"body":"So elliptical galaxies seem very smooth,"},{"startTime":1603.06,"endTime":1605.563,"body":"but things are not always what they seem."},{"startTime":1606.62,"endTime":1608.11,"body":"Let me just take a brief diversion"},{"startTime":1608.11,"endTime":1609.88,"body":"and we'll get right back to galaxies,"},{"startTime":1609.88,"endTime":1612.49,"body":"but on the subject of space telescopes,"},{"startTime":1612.49,"endTime":1614.88,"body":"of which the Hubble Space Telescope"},{"startTime":1614.88,"endTime":1619.35,"body":"has been one of a number of"},{"startTime":1614.88,"endTime":1619.35,"body":"wonderful space telescopes."},{"startTime":1619.35,"endTime":1623.33,"body":"I wonder if like me, you"},{"startTime":1619.35,"endTime":1623.33,"body":"watched with excitement"},{"startTime":1623.33,"endTime":1624.68,"body":"on Christmas morning"},{"startTime":1624.68,"endTime":1628.2,"body":"as the James Webb Space"},{"startTime":1624.68,"endTime":1628.2,"body":"Telescope was launched."},{"startTime":1628.2,"endTime":1632.63,"body":"A truly exciting thing to"},{"startTime":1628.2,"endTime":1632.63,"body":"watch and an absolute tribute"},{"startTime":1632.63,"endTime":1637.63,"body":"to the amazing engineers who"},{"startTime":1632.63,"endTime":1637.63,"body":"just designed that launch"},{"startTime":1637.7,"endTime":1640.773,"body":"and the whole structure so brilliantly."},{"startTime":1641.87,"endTime":1643.39,"body":"It was a very exciting thing to do,"},{"startTime":1643.39,"endTime":1645.38,"body":"and when it's finally commissioned,"},{"startTime":1645.38,"endTime":1648.08,"body":"it's going, we're some"},{"startTime":1645.38,"endTime":1648.08,"body":"months away from that,"},{"startTime":1648.08,"endTime":1651.55,"body":"it will open up deeper"},{"startTime":1648.08,"endTime":1651.55,"body":"studies of the structures"},{"startTime":1651.55,"endTime":1653.43,"body":"of galaxies like this."},{"startTime":1653.43,"endTime":1655.94,"body":"But in the meantime,"},{"startTime":1653.43,"endTime":1655.94,"body":"while it's on its journey,"},{"startTime":1655.94,"endTime":1658.54,"body":"I decided it will be fun"},{"startTime":1655.94,"endTime":1658.54,"body":"to see if I could watch it."},{"startTime":1659.65,"endTime":1661.71,"body":"This is an image taken"},{"startTime":1661.71,"endTime":1664.36,"body":"with my Global Jet Watch"},{"startTime":1661.71,"endTime":1664.36,"body":"telescope in Chile,"},{"startTime":1664.36,"endTime":1667.67,"body":"and that linear streak over on the left"},{"startTime":1667.67,"endTime":1670.67,"body":"is the James Webb space telescope"},{"startTime":1670.67,"endTime":1674.763,"body":"moving towards its ultimate launch site."},{"startTime":1676.13,"endTime":1679.9,"body":"And it's a complete"},{"startTime":1676.13,"endTime":1679.9,"body":"coincidence that it traveled"},{"startTime":1679.9,"endTime":1682.14,"body":"in front of a star there,"},{"startTime":1682.14,"endTime":1686.9,"body":"but it's an interesting reminder"},{"startTime":1682.14,"endTime":1686.9,"body":"how non-sidereal it moves,"},{"startTime":1686.9,"endTime":1690.33,"body":"how differently from the movement"},{"startTime":1690.33,"endTime":1691.96,"body":"of the pattern of stars it moves."},{"startTime":1691.96,"endTime":1694.566,"body":"So we've tracked it in other images"},{"startTime":1694.566,"endTime":1697.34,"body":"and in common with a lot of people,"},{"startTime":1697.34,"endTime":1701.84,"body":"we're happy to see that it's"},{"startTime":1697.34,"endTime":1701.84,"body":"still en route to success."},{"startTime":1701.84,"endTime":1704.39,"body":"End of diversion on space telescopes."},{"startTime":1704.39,"endTime":1707.49,"body":"Now let's look at spiral galaxies."},{"startTime":1707.49,"endTime":1709.87,"body":"Spiral galaxies are the pretty ones."},{"startTime":1709.87,"endTime":1712.29,"body":"They have amazing structures,"},{"startTime":1712.29,"endTime":1717.09,"body":"as you can see in this"},{"startTime":1712.29,"endTime":1717.09,"body":"beautiful example of Messier 33,"},{"startTime":1717.09,"endTime":1718.64,"body":"shown here."},{"startTime":1718.64,"endTime":1721.71,"body":"This is another galaxy in our local group."},{"startTime":1721.71,"endTime":1724.95,"body":"It's third in brightness"},{"startTime":1721.71,"endTime":1724.95,"body":"after, of course, Andromeda"},{"startTime":1724.95,"endTime":1726.173,"body":"and the Milky Way."},{"startTime":1727.23,"endTime":1730.04,"body":"And I want to remind you at this point"},{"startTime":1730.04,"endTime":1731.88,"body":"that the structure that you see here"},{"startTime":1731.88,"endTime":1735.273,"body":"is not a static pattern."},{"startTime":1736.92,"endTime":1739.76,"body":"The gas and the stars within the galaxies"},{"startTime":1739.76,"endTime":1744.76,"body":"are all orbiting around the"},{"startTime":1739.76,"endTime":1744.76,"body":"center of mass of the galaxy."},{"startTime":1745.92,"endTime":1750.72,"body":"Those stars and the gas"},{"startTime":1745.92,"endTime":1750.72,"body":"are undergoing revolution"},{"startTime":1750.72,"endTime":1752.353,"body":"around the center."},{"startTime":1753.96,"endTime":1758.96,"body":"So this is one example"},{"startTime":1753.96,"endTime":1758.96,"body":"of a spiral galaxy, M33."},{"startTime":1759.68,"endTime":1763.73,"body":"Here is another one, this is NGC 1300."},{"startTime":1763.73,"endTime":1765.14,"body":"And what's different about this one,"},{"startTime":1765.14,"endTime":1770.14,"body":"which by the way, is over"},{"startTime":1765.14,"endTime":1770.14,"body":"110,000 light years across,"},{"startTime":1770.9,"endTime":1775.9,"body":"this one has a bit of a bar"},{"startTime":1770.9,"endTime":1775.9,"body":"before the spiral arms start."},{"startTime":1776.03,"endTime":1779.46,"body":"In the previous image,"},{"startTime":1776.03,"endTime":1779.46,"body":"the arms seem to emanate"},{"startTime":1779.46,"endTime":1781.66,"body":"from very close to the center,"},{"startTime":1781.66,"endTime":1784.01,"body":"but in this one, there is most definitely,"},{"startTime":1784.01,"endTime":1787.03,"body":"again from the Global Jet"},{"startTime":1784.01,"endTime":1787.03,"body":"Watch telescope in Chile,"},{"startTime":1787.03,"endTime":1789.53,"body":"the arms don't seem to start"},{"startTime":1789.53,"endTime":1792.053,"body":"until you get to the"},{"startTime":1789.53,"endTime":1792.053,"body":"end of that bar feature."},{"startTime":1793.13,"endTime":1797.64,"body":"And this is because the"},{"startTime":1793.13,"endTime":1797.64,"body":"orbits of stars and gas"},{"startTime":1797.64,"endTime":1800.72,"body":"within a spiral galaxy can be,"},{"startTime":1800.72,"endTime":1805.72,"body":"according to the local"},{"startTime":1800.72,"endTime":1805.72,"body":"conditions, can be very unstable."},{"startTime":1806.07,"endTime":1808.85,"body":"And so that means that"},{"startTime":1806.07,"endTime":1808.85,"body":"rather than preserving"},{"startTime":1808.85,"endTime":1810.44,"body":"the beauty of the spiral arms,"},{"startTime":1810.44,"endTime":1814.47,"body":"they can collapse in and"},{"startTime":1810.44,"endTime":1814.47,"body":"form a linear feature"},{"startTime":1814.47,"endTime":1816.35,"body":"that we call a bar."},{"startTime":1816.35,"endTime":1818.21,"body":"But that has interesting consequences,"},{"startTime":1818.21,"endTime":1822.78,"body":"because you're feeding mass"},{"startTime":1818.21,"endTime":1822.78,"body":"in the form of gas and stars"},{"startTime":1822.78,"endTime":1827.193,"body":"to whatever it is that is at"},{"startTime":1822.78,"endTime":1827.193,"body":"the center of that galaxy."},{"startTime":1827.193,"endTime":1830.35,"body":"And, of course, that"},{"startTime":1827.193,"endTime":1830.35,"body":"can be a big black hole."},{"startTime":1830.35,"endTime":1834.23,"body":"And so that can give"},{"startTime":1830.35,"endTime":1834.23,"body":"rise to an active galaxy,"},{"startTime":1834.23,"endTime":1836.51,"body":"but more of that another day."},{"startTime":1836.51,"endTime":1839.34,"body":"Bars in galaxies are very much a thing."},{"startTime":1839.34,"endTime":1844.34,"body":"This is known as the Grand Barred Spiral."},{"startTime":1845.39,"endTime":1850.39,"body":"This is NGC 1365 in the"},{"startTime":1845.39,"endTime":1850.39,"body":"Fornax cluster of galaxies."},{"startTime":1850.69,"endTime":1853.5,"body":"And if I hold that image in your mind,"},{"startTime":1853.5,"endTime":1857.87,"body":"and this is the neighborhood"},{"startTime":1853.5,"endTime":1857.87,"body":"for that galaxy."},{"startTime":1857.87,"endTime":1862.26,"body":"So that galaxy is NGC"},{"startTime":1857.87,"endTime":1862.26,"body":"1365 in the bottom right,"},{"startTime":1862.26,"endTime":1864.4,"body":"this is the neighborhood."},{"startTime":1864.4,"endTime":1868.433,"body":"Anything on this image that"},{"startTime":1864.4,"endTime":1868.433,"body":"doesn't look like a point,"},{"startTime":1869.82,"endTime":1871.94,"body":"a point, of course, being a star,"},{"startTime":1871.94,"endTime":1874.87,"body":"anything that doesn't look"},{"startTime":1871.94,"endTime":1874.87,"body":"like a point is a galaxy."},{"startTime":1874.87,"endTime":1877.39,"body":"So the pull that you get"},{"startTime":1877.39,"endTime":1881.58,"body":"is going to influence the other galaxies."},{"startTime":1881.58,"endTime":1885.61,"body":"And, in fact, if you have"},{"startTime":1881.58,"endTime":1885.61,"body":"interactions with galaxy,"},{"startTime":1885.61,"endTime":1887.4,"body":"galaxy interactions,"},{"startTime":1887.4,"endTime":1890.553,"body":"you can induce these spiral structures."},{"startTime":1891.73,"endTime":1895.89,"body":"These are via so-called"},{"startTime":1891.73,"endTime":1895.89,"body":"tidal interactions."},{"startTime":1895.89,"endTime":1900.38,"body":"Interactions that vary across"},{"startTime":1895.89,"endTime":1900.38,"body":"a particular structure,"},{"startTime":1900.38,"endTime":1904.25,"body":"in much the same way that"},{"startTime":1900.38,"endTime":1904.25,"body":"we have a tidal influence"},{"startTime":1904.25,"endTime":1907.87,"body":"from the sun and the moon"},{"startTime":1904.25,"endTime":1907.87,"body":"on the oceans of Earth,"},{"startTime":1907.87,"endTime":1909.21,"body":"and on the land of Earth."},{"startTime":1909.21,"endTime":1913.14,"body":"But we see it most visibly"},{"startTime":1909.21,"endTime":1913.14,"body":"in the oceans of Earth."},{"startTime":1913.14,"endTime":1917.16,"body":"These tidal interactions"},{"startTime":1913.14,"endTime":1917.16,"body":"can distort orbits"},{"startTime":1917.16,"endTime":1921.623,"body":"and can cause orbits to"},{"startTime":1917.16,"endTime":1921.623,"body":"precess in interesting ways."},{"startTime":1922.74,"endTime":1926.34,"body":"So let's start by thinking"},{"startTime":1922.74,"endTime":1926.34,"body":"about a circular orbit"},{"startTime":1926.34,"endTime":1930.71,"body":"of a star or stellar"},{"startTime":1926.34,"endTime":1930.71,"body":"cluster within a galaxy"},{"startTime":1930.71,"endTime":1932.866,"body":"on a circular orbit."},{"startTime":1932.866,"endTime":1935.77,"body":"But of course, it doesn't"},{"startTime":1932.866,"endTime":1935.77,"body":"have to be a circular orbit,"},{"startTime":1935.77,"endTime":1938.08,"body":"and depending on the initial conditions,"},{"startTime":1938.08,"endTime":1940.84,"body":"meaning the initial dynamical conditions,"},{"startTime":1940.84,"endTime":1943.36,"body":"and the subsequent dynamical history,"},{"startTime":1943.36,"endTime":1946.35,"body":"you may not have circular orbits."},{"startTime":1946.35,"endTime":1948.463,"body":"You may have elliptical orbits."},{"startTime":1949.317,"endTime":1951.49,"body":"I'm not suggesting or I'm"},{"startTime":1949.317,"endTime":1951.49,"body":"not wishing to suggest"},{"startTime":1951.49,"endTime":1955.15,"body":"the evolution from circular"},{"startTime":1951.49,"endTime":1955.15,"body":"to elliptical takes this form,"},{"startTime":1955.15,"endTime":1956.5,"body":"I'm just trying to say"},{"startTime":1956.5,"endTime":1959.68,"body":"that there are lots of"},{"startTime":1956.5,"endTime":1959.68,"body":"different shapes of orbits,"},{"startTime":1959.68,"endTime":1963.83,"body":"lots of different ellipticities"},{"startTime":1959.68,"endTime":1963.83,"body":"or eccentricities of orbits"},{"startTime":1963.83,"endTime":1965.79,"body":"that could be at play."},{"startTime":1965.79,"endTime":1970.35,"body":"Now imagine that they"},{"startTime":1965.79,"endTime":1970.35,"body":"start to precess around,"},{"startTime":1970.35,"endTime":1971.74,"body":"and as they precess,"},{"startTime":1973.389,"endTime":1978.13,"body":"if they precess differentially"},{"startTime":1973.389,"endTime":1978.13,"body":"from one another,"},{"startTime":1978.13,"endTime":1980.98,"body":"then you can see a structure here"},{"startTime":1980.98,"endTime":1985.98,"body":"that perhaps is reminiscent"},{"startTime":1980.98,"endTime":1985.98,"body":"of the way spiral arms form."},{"startTime":1986.0,"endTime":1988.61,"body":"What you see here is on the final frame,"},{"startTime":1988.61,"endTime":1990.76,"body":"I'll keep this movie on loop,"},{"startTime":1990.76,"endTime":1995.76,"body":"What you see in that final"},{"startTime":1990.76,"endTime":1995.76,"body":"frame is a beautiful structure"},{"startTime":1996.37,"endTime":1999.13,"body":"that's reminiscent of the kind of shape"},{"startTime":1999.13,"endTime":2001.44,"body":"that you can get from a harmonograph."},{"startTime":2001.44,"endTime":2004.29,"body":"But, in fact, this is"},{"startTime":2001.44,"endTime":2004.29,"body":"coming from the precession"},{"startTime":2004.29,"endTime":2008.67,"body":"of elliptical orbits, all within a galaxy."},{"startTime":2008.67,"endTime":2012.34,"body":"If only we could observe galaxies evolving"},{"startTime":2012.34,"endTime":2015.68,"body":"on the timescales in which"},{"startTime":2012.34,"endTime":2015.68,"body":"they actually evolve,"},{"startTime":2015.68,"endTime":2019.193,"body":"it would be a wonderful thing,"},{"startTime":2015.68,"endTime":2019.193,"body":"but, of course, we can't,"},{"startTime":2020.06,"endTime":2023.453,"body":"but we can, with the"},{"startTime":2020.06,"endTime":2023.453,"body":"benefit of simulations,"},{"startTime":2024.96,"endTime":2028.89,"body":"we can hope to confront,"},{"startTime":2028.89,"endTime":2033.5,"body":"by simulations I mean calculations,"},{"startTime":2028.89,"endTime":2033.5,"body":"numerical simulations."},{"startTime":2033.5,"endTime":2038.1,"body":"We can hope to verify our"},{"startTime":2033.5,"endTime":2038.1,"body":"understanding of the orbits"},{"startTime":2038.1,"endTime":2040.16,"body":"and the interactions and the structures"},{"startTime":2040.16,"endTime":2042.32,"body":"that they give rise to."},{"startTime":2042.32,"endTime":2045.55,"body":"So let's now look at some other ways"},{"startTime":2045.55,"endTime":2048.93,"body":"in which title interactions"},{"startTime":2045.55,"endTime":2048.93,"body":"can distort orbits"},{"startTime":2048.93,"endTime":2051.01,"body":"and induce spirals."},{"startTime":2051.01,"endTime":2054.98,"body":"So if the lights go down"},{"startTime":2051.01,"endTime":2054.98,"body":"for this next movie,"},{"startTime":2054.98,"endTime":2059.27,"body":"then imagine that we start off"},{"startTime":2054.98,"endTime":2059.27,"body":"with two elliptical galaxies"},{"startTime":2059.27,"endTime":2061.43,"body":"and as they do that fly past,"},{"startTime":2061.43,"endTime":2066.33,"body":"the differential gravitational"},{"startTime":2061.43,"endTime":2066.33,"body":"forces that they feel"},{"startTime":2066.33,"endTime":2071.33,"body":"rips them apart, but in ways"},{"startTime":2066.33,"endTime":2071.33,"body":"that have beautiful symmetry."},{"startTime":2072.78,"endTime":2075.22,"body":"And there's something of"},{"startTime":2072.78,"endTime":2075.22,"body":"a simple harmonic motion."},{"startTime":2075.22,"endTime":2076.55,"body":"It's not that simple actually,"},{"startTime":2076.55,"endTime":2080.81,"body":"but I hope it reminds you"},{"startTime":2076.55,"endTime":2080.81,"body":"of simple harmonic motion"},{"startTime":2080.81,"endTime":2084.873,"body":"where gravitational masses"},{"startTime":2080.81,"endTime":2084.873,"body":"attract one another."},{"startTime":2086.01,"endTime":2087.94,"body":"They fly past, they go out,"},{"startTime":2087.94,"endTime":2090.023,"body":"that potential energy that they have,"},{"startTime":2091.09,"endTime":2094.15,"body":"ultimately gets converted back"},{"startTime":2091.09,"endTime":2094.15,"body":"into kinetic energy again."},{"startTime":2094.15,"endTime":2097.86,"body":"And, of course, the"},{"startTime":2094.15,"endTime":2097.86,"body":"dissipation will end up meaning"},{"startTime":2097.86,"endTime":2102.86,"body":"that you see a slightly"},{"startTime":2097.86,"endTime":2102.86,"body":"irregular galaxy, much like this,"},{"startTime":2103.22,"endTime":2108.22,"body":"albeit one with streaks"},{"startTime":2103.22,"endTime":2108.22,"body":"and, indeed, antennae"},{"startTime":2108.36,"endTime":2112.62,"body":"that we can hope to"},{"startTime":2108.36,"endTime":2112.62,"body":"match up to observation."},{"startTime":2112.62,"endTime":2115.83,"body":"So this is a numerical simulation"},{"startTime":2115.83,"endTime":2118.29,"body":"because the timescales"},{"startTime":2115.83,"endTime":2118.29,"body":"in which they happen"},{"startTime":2118.29,"endTime":2122.87,"body":"are vastly in excess of human timescales,"},{"startTime":2122.87,"endTime":2126.77,"body":"but simulations, numerical calculations"},{"startTime":2126.77,"endTime":2130.66,"body":"transcend our limited view of time"},{"startTime":2130.66,"endTime":2134.16,"body":"by indicating the past and the future"},{"startTime":2134.16,"endTime":2136.7,"body":"of such galaxy galaxy encounters."},{"startTime":2136.7,"endTime":2139.55,"body":"And then I hope you can see,"},{"startTime":2139.55,"endTime":2142.22,"body":"if the lights could possibly"},{"startTime":2139.55,"endTime":2142.22,"body":"go down again, thank you,"},{"startTime":2142.22,"endTime":2147.043,"body":"I hope you can see a"},{"startTime":2142.22,"endTime":2147.043,"body":"faint linear streaks here"},{"startTime":2147.043,"endTime":2150.04,"body":"that are absolutely characteristic"},{"startTime":2150.04,"endTime":2155.04,"body":"of this interacting pair of galaxies,"},{"startTime":2155.5,"endTime":2158.31,"body":"which is known as the Antennae Galaxy,"},{"startTime":2158.31,"endTime":2162.97,"body":"discovered by William Herschel in 1785."},{"startTime":2162.97,"endTime":2166.72,"body":"These galaxies are currently going through"},{"startTime":2166.72,"endTime":2168.24,"body":"a star formation phase,"},{"startTime":2168.24,"endTime":2171.11,"body":"what we call a star burst phase,"},{"startTime":2171.11,"endTime":2174.23,"body":"because as they collided together,"},{"startTime":2174.23,"endTime":2179.23,"body":"you've compressed the gas"},{"startTime":2174.23,"endTime":2179.23,"body":"that both galaxies contained,"},{"startTime":2179.38,"endTime":2182.08,"body":"you've increase the density of the gas."},{"startTime":2182.08,"endTime":2186.22,"body":"And as we know, dense gas,"},{"startTime":2182.08,"endTime":2186.22,"body":"if there's enough of it,"},{"startTime":2186.22,"endTime":2188.2,"body":"and if it's not too hot,"},{"startTime":2188.2,"endTime":2191.72,"body":"will give rise to the formation of stars."},{"startTime":2191.72,"endTime":2195.46,"body":"So lots of ongoing star formation"},{"startTime":2191.72,"endTime":2195.46,"body":"in those brighter regions"},{"startTime":2195.46,"endTime":2196.913,"body":"of the Antennae Galaxy."},{"startTime":2198.17,"endTime":2200.47,"body":"Now it was believed for many years,"},{"startTime":2200.47,"endTime":2204.51,"body":"after Hubble constructed"},{"startTime":2200.47,"endTime":2204.51,"body":"this particular diagram,"},{"startTime":2204.51,"endTime":2208.13,"body":"known for fairly obvious reasons"},{"startTime":2204.51,"endTime":2208.13,"body":"as the tuning fork diagram,"},{"startTime":2208.13,"endTime":2209.76,"body":"because of its shape,"},{"startTime":2209.76,"endTime":2214.11,"body":"that galaxies would evolve"},{"startTime":2209.76,"endTime":2214.11,"body":"pretty much from left to right"},{"startTime":2214.11,"endTime":2217.21,"body":"across the image, with"},{"startTime":2214.11,"endTime":2217.21,"body":"the very smooth structures"},{"startTime":2217.21,"endTime":2221.12,"body":"being on the left and the pretty"},{"startTime":2217.21,"endTime":2221.12,"body":"spirals and barred spirals"},{"startTime":2221.12,"endTime":2222.133,"body":"being on the right."},{"startTime":2223.89,"endTime":2226.053,"body":"That was what people used to think."},{"startTime":2227.0,"endTime":2229.59,"body":"And so now I want to revisit that question"},{"startTime":2229.59,"endTime":2234.59,"body":"of are galaxies, are elliptical galaxies,"},{"startTime":2234.75,"endTime":2239.33,"body":"smooth, elliptical galaxies"},{"startTime":2234.75,"endTime":2239.33,"body":"all that they seem?"},{"startTime":2239.33,"endTime":2243.42,"body":"Well, again on the face"},{"startTime":2239.33,"endTime":2243.42,"body":"of it, they look smooth."},{"startTime":2243.42,"endTime":2245.943,"body":"They don't look exactly like spilled milk."},{"startTime":2246.8,"endTime":2249.13,"body":"So, you know, the Greek name for them"},{"startTime":2249.13,"endTime":2251.45,"body":"doesn't seem quite right, but nonetheless,"},{"startTime":2251.45,"endTime":2254.393,"body":"we would agree they are"},{"startTime":2251.45,"endTime":2254.393,"body":"smooth and somewhat creamy."},{"startTime":2255.43,"endTime":2259.8,"body":"Now imagine that you look at"},{"startTime":2255.43,"endTime":2259.8,"body":"these elliptical galaxies,"},{"startTime":2259.8,"endTime":2261.97,"body":"not just with an imaging camera,"},{"startTime":2261.97,"endTime":2264.68,"body":"so not just taking a photograph,"},{"startTime":2264.68,"endTime":2267.41,"body":"but you look at them with an instrument"},{"startTime":2267.41,"endTime":2269.54,"body":"called a spectrograph,"},{"startTime":2269.54,"endTime":2272.33,"body":"an instrument that splits up the light"},{"startTime":2272.33,"endTime":2275.223,"body":"as a function of color or wavelength,"},{"startTime":2276.08,"endTime":2280.23,"body":"which as I described in"},{"startTime":2276.08,"endTime":2280.23,"body":"my lecture a year ago"},{"startTime":2280.23,"endTime":2282.75,"body":"in the series called Cosmic Vision,"},{"startTime":2282.75,"endTime":2284.74,"body":"and called Unraveling Rainbows,"},{"startTime":2284.74,"endTime":2288.25,"body":"when you split up light"},{"startTime":2284.74,"endTime":2288.25,"body":"into different colors"},{"startTime":2288.25,"endTime":2289.68,"body":"and different wavelengths,"},{"startTime":2289.68,"endTime":2292.6,"body":"you get information about dynamics,"},{"startTime":2292.6,"endTime":2296.63,"body":"and dynamics is fantastically exciting."},{"startTime":2296.63,"endTime":2299.9,"body":"So now imagine that you look all the way"},{"startTime":2299.9,"endTime":2302.25,"body":"across these galaxies,"},{"startTime":2302.25,"endTime":2306.65,"body":"these seemingly smooth elliptical galaxies"},{"startTime":2306.65,"endTime":2308.61,"body":"that I'm showing you here,"},{"startTime":2308.61,"endTime":2310.81,"body":"with an instrument that"},{"startTime":2308.61,"endTime":2310.81,"body":"can split up the light"},{"startTime":2310.81,"endTime":2313.07,"body":"from all the different pixels,"},{"startTime":2313.07,"endTime":2316.2,"body":"all the different regions"},{"startTime":2313.07,"endTime":2316.2,"body":"across each of these galaxies"},{"startTime":2316.2,"endTime":2317.83,"body":"and address the question,"},{"startTime":2317.83,"endTime":2321.8,"body":"what are the dynamics of"},{"startTime":2317.83,"endTime":2321.8,"body":"that bit of the galaxy"},{"startTime":2321.8,"endTime":2324.24,"body":"relative to us here on Earth?"},{"startTime":2324.24,"endTime":2326.65,"body":"So let's take the central galaxy."},{"startTime":2326.65,"endTime":2329.81,"body":"Let's imagine we're looking"},{"startTime":2326.65,"endTime":2329.81,"body":"at a particular feature"},{"startTime":2329.81,"endTime":2334.7,"body":"in the spectrum, and you"},{"startTime":2329.81,"endTime":2334.7,"body":"see something remarkable."},{"startTime":2334.7,"endTime":2338.21,"body":"Some of the gas that's"},{"startTime":2334.7,"endTime":2338.21,"body":"slightly on the lower left,"},{"startTime":2338.21,"endTime":2343.12,"body":"color-coded blue here"},{"startTime":2338.21,"endTime":2343.12,"body":"is moving towards Earth,"},{"startTime":2343.12,"endTime":2345.79,"body":"but the material that's color-coded red,"},{"startTime":2345.79,"endTime":2348.81,"body":"you should regard this"},{"startTime":2345.79,"endTime":2348.81,"body":"as being super imposed"},{"startTime":2348.81,"endTime":2350.69,"body":"on that background image."},{"startTime":2350.69,"endTime":2353.533,"body":"The dynamical information is"},{"startTime":2350.69,"endTime":2353.533,"body":"imposed on the photograph,"},{"startTime":2354.68,"endTime":2358.53,"body":"the material that's color-coded"},{"startTime":2354.68,"endTime":2358.53,"body":"red is going away from us."},{"startTime":2358.53,"endTime":2362.08,"body":"So what you've actually got is rotation."},{"startTime":2362.08,"endTime":2365.157,"body":"You can see the characteristic"},{"startTime":2362.08,"endTime":2365.157,"body":"signature of the gas"},{"startTime":2365.157,"endTime":2369.95,"body":"and stars coming towards Earth"},{"startTime":2365.157,"endTime":2369.95,"body":"and moving away from Earth."},{"startTime":2369.95,"endTime":2372.53,"body":"And it's not just this example,"},{"startTime":2372.53,"endTime":2375.59,"body":"it's also in this example"},{"startTime":2372.53,"endTime":2375.59,"body":"here on the right,"},{"startTime":2375.59,"endTime":2378.02,"body":"unfortunately the field of view"},{"startTime":2378.02,"endTime":2379.83,"body":"of the particular type of spectrograph"},{"startTime":2379.83,"endTime":2381.967,"body":"didn't cover the entire galaxy,"},{"startTime":2381.967,"endTime":2385.12,"body":"but you can see where"},{"startTime":2381.967,"endTime":2385.12,"body":"it's blue on the left,"},{"startTime":2385.12,"endTime":2386.83,"body":"where it's red on the right."},{"startTime":2386.83,"endTime":2390.89,"body":"You've got significant revolution."},{"startTime":2390.89,"endTime":2394.0,"body":"You've got rotation in"},{"startTime":2390.89,"endTime":2394.0,"body":"the gas and the stars."},{"startTime":2394.0,"endTime":2398.03,"body":"So despite the seemingly smooth appearance"},{"startTime":2398.03,"endTime":2401.91,"body":"of the elliptical galaxies,"},{"startTime":2398.03,"endTime":2401.91,"body":"they are rotating."},{"startTime":2401.91,"endTime":2404.86,"body":"If only you measure them in such a way"},{"startTime":2404.86,"endTime":2407.673,"body":"that you can see the rotation is there."},{"startTime":2408.53,"endTime":2411.59,"body":"The actual characteristics"},{"startTime":2408.53,"endTime":2411.59,"body":"of the revolution"},{"startTime":2411.59,"endTime":2414.09,"body":"and the rotation are as different"},{"startTime":2414.09,"endTime":2416.07,"body":"as every galaxy is different."},{"startTime":2416.07,"endTime":2419.33,"body":"In this case, there's"},{"startTime":2416.07,"endTime":2419.33,"body":"a little bit of a sense"},{"startTime":2419.33,"endTime":2424.3,"body":"of very gentle rotation"},{"startTime":2419.33,"endTime":2424.3,"body":"on the right-hand side,"},{"startTime":2424.3,"endTime":2428.78,"body":"slightly more dark blue"},{"startTime":2424.3,"endTime":2428.78,"body":"than on the left-hand side."},{"startTime":2428.78,"endTime":2433.78,"body":"So this right-hand side is"},{"startTime":2428.78,"endTime":2433.78,"body":"slightly, or rather slowly,"},{"startTime":2434.43,"endTime":2436.0,"body":"coming towards Earth."},{"startTime":2436.0,"endTime":2440.07,"body":"The slight smattering of red"},{"startTime":2436.0,"endTime":2440.07,"body":"pixels on the left-hand side"},{"startTime":2440.07,"endTime":2445.07,"body":"of this right galaxy"},{"startTime":2440.07,"endTime":2445.07,"body":"rotating away from Earth."},{"startTime":2445.15,"endTime":2448.08,"body":"So despite the seemingly"},{"startTime":2445.15,"endTime":2448.08,"body":"smooth structures,"},{"startTime":2448.08,"endTime":2452.68,"body":"there is rotation within and"},{"startTime":2448.08,"endTime":2452.68,"body":"where you have rotation within,"},{"startTime":2452.68,"endTime":2456.37,"body":"that's a bit of a hint"},{"startTime":2452.68,"endTime":2456.37,"body":"of galaxy interactions"},{"startTime":2457.24,"endTime":2462.02,"body":"being responsible for the"},{"startTime":2457.24,"endTime":2462.02,"body":"overall dynamical structure"},{"startTime":2462.02,"endTime":2465.87,"body":"and brightness structure"},{"startTime":2462.02,"endTime":2465.87,"body":"that we see today."},{"startTime":2465.87,"endTime":2468.72,"body":"So a bit of a modification, indeed,"},{"startTime":2468.72,"endTime":2471.32,"body":"an intellectual revolution"},{"startTime":2471.32,"endTime":2476.32,"body":"of the original Hubble tuning"},{"startTime":2471.32,"endTime":2476.32,"body":"fork diagram was called for."},{"startTime":2477.86,"endTime":2482.46,"body":"And so some work done by one"},{"startTime":2477.86,"endTime":2482.46,"body":"of my colleagues in Oxford,"},{"startTime":2482.46,"endTime":2486.85,"body":"Michele Cappallari, has done just that."},{"startTime":2486.85,"endTime":2488.24,"body":"So rather than saying,"},{"startTime":2488.24,"endTime":2491.94,"body":"okay, well gradually we"},{"startTime":2488.24,"endTime":2491.94,"body":"go from left to right,"},{"startTime":2491.94,"endTime":2494.85,"body":"as galaxies sort of settle down"},{"startTime":2494.85,"endTime":2498.89,"body":"and form these spiral galaxies"},{"startTime":2494.85,"endTime":2498.89,"body":"in their pretty discs."},{"startTime":2498.89,"endTime":2502.29,"body":"There's more to it than"},{"startTime":2498.89,"endTime":2502.29,"body":"that, unsurprisingly,"},{"startTime":2502.29,"endTime":2507.29,"body":"and rotation revolution is the"},{"startTime":2502.29,"endTime":2507.29,"body":"key to understanding those."},{"startTime":2507.79,"endTime":2511.71,"body":"So really the axis from left to right"},{"startTime":2511.71,"endTime":2515.53,"body":"isn't so much who formed first,"},{"startTime":2515.53,"endTime":2520.06,"body":"but it's rather, how"},{"startTime":2515.53,"endTime":2520.06,"body":"rapidly are you revolving?"},{"startTime":2520.06,"endTime":2523.763,"body":"How rapidly is that galaxy rotating?"},{"startTime":2525.03,"endTime":2527.84,"body":"And it's not just galaxy"},{"startTime":2525.03,"endTime":2527.84,"body":"galaxy interactions"},{"startTime":2527.84,"endTime":2532.787,"body":"that give rise to revolving"},{"startTime":2527.84,"endTime":2532.787,"body":"rotating material within."},{"startTime":2533.64,"endTime":2536.91,"body":"Maybe, maybe that's simply telling you"},{"startTime":2536.91,"endTime":2540.78,"body":"about the rotation of"},{"startTime":2536.91,"endTime":2540.78,"body":"that massive gas cloud,"},{"startTime":2540.78,"endTime":2543.97,"body":"which initially collapsed under gravity"},{"startTime":2543.97,"endTime":2548.97,"body":"and on an individual basis,"},{"startTime":2543.97,"endTime":2548.97,"body":"formed all the stars within,"},{"startTime":2549.46,"endTime":2554.22,"body":"out of that gas, which"},{"startTime":2549.46,"endTime":2554.22,"body":"itself had a net rotation."},{"startTime":2554.22,"endTime":2557.78,"body":"So for sure, rotation is telling us"},{"startTime":2557.78,"endTime":2561.38,"body":"about a combination of"},{"startTime":2557.78,"endTime":2561.38,"body":"the initial conditions"},{"startTime":2561.38,"endTime":2565.81,"body":"and the ongoing dynamical interactions"},{"startTime":2565.81,"endTime":2568.91,"body":"that a galaxy may or may not"},{"startTime":2565.81,"endTime":2568.91,"body":"have had with its neighbors"},{"startTime":2569.76,"endTime":2571.6,"body":"if it's in a cluster."},{"startTime":2571.6,"endTime":2574.4,"body":"And so the really fast rotators"},{"startTime":2574.4,"endTime":2577.5,"body":"are indeed the pretty spiral galaxies,"},{"startTime":2577.5,"endTime":2580.92,"body":"the ones that form"},{"startTime":2577.5,"endTime":2580.92,"body":"these amazing structures"},{"startTime":2580.92,"endTime":2584.06,"body":"that I showed you different images of."},{"startTime":2584.06,"endTime":2588.3,"body":"So this is a very important revision,"},{"startTime":2588.3,"endTime":2590.58,"body":"an intellectual revolution"},{"startTime":2590.58,"endTime":2594.52,"body":"as applied to Hubble's"},{"startTime":2590.58,"endTime":2594.52,"body":"tuning fork diagram,"},{"startTime":2594.52,"endTime":2597.24,"body":"which was a very intelligent suggestion."},{"startTime":2597.24,"endTime":2600.24,"body":"But, of course, in the"},{"startTime":2597.24,"endTime":2600.24,"body":"light of new information,"},{"startTime":2600.24,"endTime":2603.54,"body":"which we now have,"},{"startTime":2600.24,"endTime":2603.54,"body":"spectroscopic information,"},{"startTime":2603.54,"endTime":2607.26,"body":"dynamical information, in the"},{"startTime":2603.54,"endTime":2607.26,"body":"light of that new information,"},{"startTime":2607.26,"endTime":2609.49,"body":"we change our minds."},{"startTime":2609.49,"endTime":2613.69,"body":"So this was work which my"},{"startTime":2609.49,"endTime":2613.69,"body":"colleague Michele Cappallari led"},{"startTime":2613.69,"endTime":2617.72,"body":"as part of a big survey called Atlas 3D,"},{"startTime":2617.72,"endTime":2620.32,"body":"trying to get at the 3D structures,"},{"startTime":2620.32,"endTime":2625.32,"body":"the rotating structures of,"},{"startTime":2620.32,"endTime":2625.32,"body":"it was over 200 galaxies"},{"startTime":2625.32,"endTime":2627.91,"body":"that they investigated in this way"},{"startTime":2627.91,"endTime":2630.76,"body":"to reach the conclusion that is summarized"},{"startTime":2630.76,"endTime":2632.703,"body":"in this diagram on the right."},{"startTime":2633.98,"endTime":2636.37,"body":"Well now let's zoom out"},{"startTime":2633.98,"endTime":2636.37,"body":"a bit further still,"},{"startTime":2636.37,"endTime":2639.69,"body":"not just galaxies and"},{"startTime":2636.37,"endTime":2639.69,"body":"clusters of galaxies,"},{"startTime":2639.69,"endTime":2644.69,"body":"but to larger scale structures still."},{"startTime":2645.16,"endTime":2649.75,"body":"We live in a hierarchical universe."},{"startTime":2649.75,"endTime":2653.19,"body":"We don't just have clusters of galaxies,"},{"startTime":2653.19,"endTime":2656.69,"body":"but we have hierarchical"},{"startTime":2653.19,"endTime":2656.69,"body":"structures beyond that."},{"startTime":2656.69,"endTime":2661.69,"body":"We have clusters of clusters of galaxies."},{"startTime":2662.13,"endTime":2664.14,"body":"Everything in the"},{"startTime":2662.13,"endTime":2664.14,"body":"universe seems to be part"},{"startTime":2664.14,"endTime":2666.25,"body":"of something bigger."},{"startTime":2666.25,"endTime":2667.94,"body":"Earth is part of the solar system."},{"startTime":2667.94,"endTime":2670.02,"body":"The solar system is part of the Milky Way."},{"startTime":2670.02,"endTime":2672.85,"body":"The Milky Way is part of the"},{"startTime":2670.02,"endTime":2672.85,"body":"local group with Andromeda,"},{"startTime":2672.85,"endTime":2674.22,"body":"and the Large Magellanic Cloud"},{"startTime":2674.22,"endTime":2677.21,"body":"and the Small Magellanic Cloud and M33."},{"startTime":2677.21,"endTime":2679.593,"body":"The local group is part"},{"startTime":2677.21,"endTime":2679.593,"body":"of the Virgo cluster,"},{"startTime":2680.82,"endTime":2682.6,"body":"But ultimately you get"},{"startTime":2682.6,"endTime":2686.79,"body":"to these clusters of clusters of galaxies."},{"startTime":2686.79,"endTime":2690.88,"body":"These also are known by"},{"startTime":2686.79,"endTime":2690.88,"body":"the name superclusters,"},{"startTime":2690.88,"endTime":2695.78,"body":"and these can be hundreds"},{"startTime":2690.88,"endTime":2695.78,"body":"of millions of light years"},{"startTime":2695.78,"endTime":2700.78,"body":"in extent and containing"},{"startTime":2695.78,"endTime":2700.78,"body":"millions of galaxies."},{"startTime":2702.78,"endTime":2705.823,"body":"So we're part of a supercluster,"},{"startTime":2706.75,"endTime":2711.12,"body":"the name of our cluster"},{"startTime":2706.75,"endTime":2711.12,"body":"is called Laniakea,"},{"startTime":2711.12,"endTime":2714.883,"body":"which is a Hawaiian word"},{"startTime":2711.12,"endTime":2714.883,"body":"that means immense heaven."},{"startTime":2716.08,"endTime":2721.08,"body":"And you can see why the"},{"startTime":2716.08,"endTime":2721.08,"body":"Polynesians of yesteryear"},{"startTime":2721.128,"endTime":2724.79,"body":"would make the association of immense sky."},{"startTime":2724.79,"endTime":2728.54,"body":"Not that they could observe"},{"startTime":2724.79,"endTime":2728.54,"body":"this, of course, years ago,"},{"startTime":2728.54,"endTime":2731.35,"body":"but this structure itself"},{"startTime":2728.54,"endTime":2731.35,"body":"that we are part of"},{"startTime":2733.74,"endTime":2737.11,"body":"comprises something"},{"startTime":2733.74,"endTime":2737.11,"body":"like a 100,000 galaxies"},{"startTime":2737.11,"endTime":2742.11,"body":"stretched out over something"},{"startTime":2737.11,"endTime":2742.11,"body":"like 500 million light years."},{"startTime":2744.34,"endTime":2748.69,"body":"Contained within this are something like,"},{"startTime":2748.69,"endTime":2753.69,"body":"10 to the power of 17"},{"startTime":2748.69,"endTime":2753.69,"body":"times the mass of our sun,"},{"startTime":2754.161,"endTime":2756.76,"body":"a 100,000 times the mass of our galaxy,"},{"startTime":2756.76,"endTime":2759.84,"body":"these numbers all sort of"},{"startTime":2756.76,"endTime":2759.84,"body":"go over our heads, I think,"},{"startTime":2759.84,"endTime":2762.794,"body":"but it's remarkable to"},{"startTime":2759.84,"endTime":2762.794,"body":"think that we belong"},{"startTime":2762.794,"endTime":2767.794,"body":"to this hierarchy of"},{"startTime":2762.794,"endTime":2767.794,"body":"structures and you can,"},{"startTime":2768.76,"endTime":2773.76,"body":"this is a sort of quasi 3D"},{"startTime":2768.76,"endTime":2773.76,"body":"mapping of them, of course,"},{"startTime":2775.61,"endTime":2778.16,"body":"but the local group I should say"},{"startTime":2778.16,"endTime":2779.75,"body":"is just in blue letters there."},{"startTime":2779.75,"endTime":2782.81,"body":"I don't know if you can quite"},{"startTime":2779.75,"endTime":2782.81,"body":"make it out with the contrast,"},{"startTime":2782.81,"endTime":2786.91,"body":"but that's the cluster"},{"startTime":2782.81,"endTime":2786.91,"body":"of clusters of galaxies"},{"startTime":2786.91,"endTime":2789.5,"body":"that we are part of."},{"startTime":2789.5,"endTime":2790.72,"body":"We can project this back"},{"startTime":2790.72,"endTime":2795.13,"body":"on the same original galactic coordinates"},{"startTime":2795.13,"endTime":2799.31,"body":"that I started with at"},{"startTime":2795.13,"endTime":2799.31,"body":"the very start of my talk."},{"startTime":2799.31,"endTime":2801.716,"body":"You can see the various"},{"startTime":2799.31,"endTime":2801.716,"body":"different clusters,"},{"startTime":2801.716,"endTime":2805.51,"body":"Fornex down near me here at the bottom,"},{"startTime":2805.51,"endTime":2808.38,"body":"but various different superclusters,"},{"startTime":2808.38,"endTime":2813.38,"body":"all of which the"},{"startTime":2808.38,"endTime":2813.38,"body":"membership of all of which"},{"startTime":2813.58,"endTime":2816.78,"body":"can be determined when"},{"startTime":2813.58,"endTime":2816.78,"body":"you know the distances"},{"startTime":2816.78,"endTime":2819.1,"body":"to these objects, which is something"},{"startTime":2819.1,"endTime":2821.55,"body":"that comes from spectroscopy,"},{"startTime":2821.55,"endTime":2824.29,"body":"from knowing what the components are"},{"startTime":2824.29,"endTime":2827.68,"body":"and how far away they are from us."},{"startTime":2827.68,"endTime":2830.9,"body":"So that is large scale"},{"startTime":2827.68,"endTime":2830.9,"body":"structure in, by the way,"},{"startTime":2830.9,"endTime":2833.503,"body":"still only the local universe."},{"startTime":2834.7,"endTime":2838.21,"body":"Well, I want to take a different tack now"},{"startTime":2838.21,"endTime":2843.21,"body":"and talk to something else"},{"startTime":2838.21,"endTime":2843.21,"body":"rather closer to home."},{"startTime":2844.31,"endTime":2846.05,"body":"And by way of introduction to that,"},{"startTime":2846.05,"endTime":2849.43,"body":"I want to start with something"},{"startTime":2846.05,"endTime":2849.43,"body":"that was rather shocking"},{"startTime":2849.43,"endTime":2852.16,"body":"in the news over the weekend,"},{"startTime":2852.16,"endTime":2857.16,"body":"shocking in terms of its"},{"startTime":2852.16,"endTime":2857.16,"body":"deadliness to the humans involved,"},{"startTime":2858.1,"endTime":2860.21,"body":"who were directly affected by it"},{"startTime":2860.21,"endTime":2864.73,"body":"and shocking in terms of"},{"startTime":2860.21,"endTime":2864.73,"body":"the energies involved."},{"startTime":2864.73,"endTime":2868.55,"body":"I'm talking about, of course,"},{"startTime":2864.73,"endTime":2868.55,"body":"the explosive eruption"},{"startTime":2868.55,"endTime":2873.22,"body":"of the Hunga Tonga-Hunga Hawaii volcano"},{"startTime":2873.22,"endTime":2876.81,"body":"in the South Pacific that took place."},{"startTime":2876.81,"endTime":2880.18,"body":"It's estimated that the energy involved"},{"startTime":2880.18,"endTime":2884.17,"body":"in this initially underwater volcano"},{"startTime":2884.17,"endTime":2889.17,"body":"was something like well"},{"startTime":2884.17,"endTime":2889.17,"body":"over 500 times the energy"},{"startTime":2890.53,"endTime":2893.24,"body":"of the bomb that was"},{"startTime":2890.53,"endTime":2893.24,"body":"dropped over Hiroshima"},{"startTime":2893.24,"endTime":2895.47,"body":"towards the end of the Second World War,"},{"startTime":2895.47,"endTime":2899.293,"body":"a hugely energetic event here on Earth."},{"startTime":2900.32,"endTime":2901.153,"body":"And I mention it,"},{"startTime":2901.153,"endTime":2904.34,"body":"because I want to draw your"},{"startTime":2901.153,"endTime":2904.34,"body":"attention to the shock waves,"},{"startTime":2904.34,"endTime":2908.11,"body":"the blast wave, the"},{"startTime":2904.34,"endTime":2908.11,"body":"pressure wave that emanated"},{"startTime":2908.11,"endTime":2911.26,"body":"from this volcanic explosion."},{"startTime":2911.26,"endTime":2915.33,"body":"So from its location,"},{"startTime":2911.26,"endTime":2915.33,"body":"from the location of Tonga"},{"startTime":2915.33,"endTime":2918.9,"body":"in the South Pacific,"},{"startTime":2915.33,"endTime":2918.9,"body":"the shockwave spread,"},{"startTime":2918.9,"endTime":2922.13,"body":"and within only a matter of hours"},{"startTime":2922.13,"endTime":2925.28,"body":"after the eruption shown"},{"startTime":2922.13,"endTime":2925.28,"body":"by the red dotted line"},{"startTime":2925.28,"endTime":2930.28,"body":"over on the left, only what"},{"startTime":2925.28,"endTime":2930.28,"body":"is it, six or so hours later,"},{"startTime":2932.21,"endTime":2937.21,"body":"a pressure hike and suppression,"},{"startTime":2932.21,"endTime":2937.21,"body":"a depression rather,"},{"startTime":2937.91,"endTime":2941.67,"body":"corresponding to the"},{"startTime":2937.91,"endTime":2941.67,"body":"pressure wave was picked up"},{"startTime":2941.67,"endTime":2945.6,"body":"in a nearby island in the"},{"startTime":2941.67,"endTime":2945.6,"body":"South Pacific, Norfolk Island."},{"startTime":2945.6,"endTime":2950.6,"body":"It's a bit south to Vanuatu,"},{"startTime":2945.6,"endTime":2950.6,"body":"North of New Zealand,"},{"startTime":2950.65,"endTime":2953.65,"body":"and then in Queensland"},{"startTime":2950.65,"endTime":2953.65,"body":"and in New South Wales,"},{"startTime":2953.65,"endTime":2956.22,"body":"South Australia, and"},{"startTime":2953.65,"endTime":2956.22,"body":"then some hours later,"},{"startTime":2956.22,"endTime":2960.42,"body":"Western Australia, the pressure"},{"startTime":2956.22,"endTime":2960.42,"body":"wave from that explosion"},{"startTime":2960.42,"endTime":2964.29,"body":"was picked up, and it"},{"startTime":2960.42,"endTime":2964.29,"body":"propagated around the world."},{"startTime":2964.29,"endTime":2968.42,"body":"It was picked up in Gloucestershire,"},{"startTime":2964.29,"endTime":2968.42,"body":"and in the Netherlands."},{"startTime":2968.42,"endTime":2972.41,"body":"That ripple spread around our planet,"},{"startTime":2972.41,"endTime":2974.33,"body":"such was the intensity,"},{"startTime":2974.33,"endTime":2978.23,"body":"such as the energy of that explosion."},{"startTime":2978.23,"endTime":2981.75,"body":"And so when explosions happen in space,"},{"startTime":2981.75,"endTime":2986.0,"body":"the consequences of those"},{"startTime":2981.75,"endTime":2986.0,"body":"shock waves and blast waves"},{"startTime":2986.0,"endTime":2988.98,"body":"can similarly be felt and give rise"},{"startTime":2988.98,"endTime":2993.833,"body":"to remarkable transitions"},{"startTime":2988.98,"endTime":2993.833,"body":"in that bit of the universe."},{"startTime":2994.99,"endTime":2998.08,"body":"And so another shocking"},{"startTime":2994.99,"endTime":2998.08,"body":"in the sense of startling"},{"startTime":2998.08,"endTime":3003.08,"body":"and surprising piece of news"},{"startTime":2998.08,"endTime":3003.08,"body":"in the past couple of weeks"},{"startTime":3003.41,"endTime":3006.75,"body":"is what I want to turn"},{"startTime":3003.41,"endTime":3006.75,"body":"my attention to now."},{"startTime":3006.75,"endTime":3008.96,"body":"It's been realized, it's been established"},{"startTime":3008.96,"endTime":3011.81,"body":"by scientists based at Harvard,"},{"startTime":3011.81,"endTime":3014.66,"body":"that the solar system is at the center"},{"startTime":3014.66,"endTime":3019.26,"body":"of a newly discovered structure"},{"startTime":3014.66,"endTime":3019.26,"body":"caused by a blast wave,"},{"startTime":3019.26,"endTime":3024.26,"body":"not by a volcano, but"},{"startTime":3019.26,"endTime":3024.26,"body":"instead by a supernova"},{"startTime":3024.94,"endTime":3029.94,"body":"that happened probably"},{"startTime":3024.94,"endTime":3029.94,"body":"some 14 million years ago."},{"startTime":3030.98,"endTime":3034.77,"body":"And on its boundary, on the"},{"startTime":3030.98,"endTime":3034.77,"body":"boundary of that blast wave,"},{"startTime":3034.77,"endTime":3038.83,"body":"where, remember blast waves"},{"startTime":3034.77,"endTime":3038.83,"body":"are pressure discontinuities,"},{"startTime":3038.83,"endTime":3041.41,"body":"much like when measured by the barometers"},{"startTime":3041.41,"endTime":3043.57,"body":"all across Australia, in Gloucestershire,"},{"startTime":3043.57,"endTime":3046.89,"body":"in the Netherlands, in the"},{"startTime":3043.57,"endTime":3046.89,"body":"few slides I just showed you,"},{"startTime":3046.89,"endTime":3051.75,"body":"where you get compression,"},{"startTime":3046.89,"endTime":3051.75,"body":"where you make gas more dense,"},{"startTime":3051.75,"endTime":3055.51,"body":"if it's cold enough, you"},{"startTime":3051.75,"endTime":3055.51,"body":"will trigger star formation."},{"startTime":3055.51,"endTime":3060.51,"body":"And so the solar system is"},{"startTime":3055.51,"endTime":3060.51,"body":"designed to be indicated"},{"startTime":3061.19,"endTime":3062.437,"body":"by that bright region there."},{"startTime":3062.437,"endTime":3067.437,"body":"There are these indicated by"},{"startTime":3062.437,"endTime":3067.437,"body":"the sort of bluey lilac regions"},{"startTime":3067.62,"endTime":3071.05,"body":"are regions of relatively"},{"startTime":3067.62,"endTime":3071.05,"body":"young star formation"},{"startTime":3071.05,"endTime":3073.51,"body":"that were triggered by the blast wave"},{"startTime":3073.51,"endTime":3078.0,"body":"that's indicated in the"},{"startTime":3073.51,"endTime":3078.0,"body":"sort of creamy, gray color."},{"startTime":3078.0,"endTime":3081.04,"body":"So I'm going to show you now"},{"startTime":3078.0,"endTime":3081.04,"body":"a movie that was prepared"},{"startTime":3081.04,"endTime":3085.82,"body":"by that team at Harvard"},{"startTime":3081.04,"endTime":3085.82,"body":"led by Alyssa Goodman."},{"startTime":3085.82,"endTime":3088.733,"body":"First of all, it's just showing"},{"startTime":3085.82,"endTime":3088.733,"body":"you that in the Milky Way,"},{"startTime":3089.6,"endTime":3093.11,"body":"we're getting to us here"},{"startTime":3089.6,"endTime":3093.11,"body":"to the solar neighborhood"},{"startTime":3093.11,"endTime":3097.2,"body":"or nearby it, going"},{"startTime":3093.11,"endTime":3097.2,"body":"overshooting and going past it."},{"startTime":3097.2,"endTime":3100.91,"body":"But something like 14 million years ago,"},{"startTime":3100.91,"endTime":3103.54,"body":"a supernova explosion,"},{"startTime":3103.54,"endTime":3107.64,"body":"from which a big blast wave"},{"startTime":3103.54,"endTime":3107.64,"body":"would inevitably follow."},{"startTime":3107.64,"endTime":3111.0,"body":"And you can see it expanding"},{"startTime":3107.64,"endTime":3111.0,"body":"because it's over-pressured,"},{"startTime":3111.0,"endTime":3114.4,"body":"it expands into outer space."},{"startTime":3114.4,"endTime":3118.71,"body":"And when it's sufficiently compressed gas,"},{"startTime":3118.71,"endTime":3121.403,"body":"then you can get the formation of stars."},{"startTime":3122.34,"endTime":3126.48,"body":"So 10 million years ago,"},{"startTime":3122.34,"endTime":3126.48,"body":"up rocks our solar system,"},{"startTime":3126.48,"endTime":3128.05,"body":"which is indicated by the bright light"},{"startTime":3128.05,"endTime":3129.5,"body":"going through the middle."},{"startTime":3129.5,"endTime":3132.33,"body":"And now we are careering through it."},{"startTime":3132.33,"endTime":3134.78,"body":"We're not far off the center now."},{"startTime":3134.78,"endTime":3137.719,"body":"And so all these different"},{"startTime":3134.78,"endTime":3137.719,"body":"regions in space,"},{"startTime":3137.719,"endTime":3141.08,"body":"Ophiuchus, Corona Australis, Musca,"},{"startTime":3141.08,"endTime":3145.6,"body":"that we can image from"},{"startTime":3141.08,"endTime":3145.6,"body":"Earth relatively easily."},{"startTime":3145.6,"endTime":3148.24,"body":"These regions we now understood."},{"startTime":3148.24,"endTime":3150.61,"body":"We knew about these"},{"startTime":3148.24,"endTime":3150.61,"body":"regions of star formation"},{"startTime":3150.61,"endTime":3151.98,"body":"for quite some years,"},{"startTime":3151.98,"endTime":3155.39,"body":"and it had been known"},{"startTime":3151.98,"endTime":3155.39,"body":"that the solar system"},{"startTime":3155.39,"endTime":3159.26,"body":"seems to be at the center of our void."},{"startTime":3159.26,"endTime":3163.12,"body":"But the startling announcement"},{"startTime":3159.26,"endTime":3163.12,"body":"of a couple of weeks ago"},{"startTime":3163.12,"endTime":3167.85,"body":"was very much that that void"},{"startTime":3163.12,"endTime":3167.85,"body":"was created by the blast wave"},{"startTime":3167.85,"endTime":3171.07,"body":"of a supernova remnant"},{"startTime":3171.07,"endTime":3174.163,"body":"that gave rise to the"},{"startTime":3171.07,"endTime":3174.163,"body":"amazing structure we see."},{"startTime":3175.28,"endTime":3177.31,"body":"I do hope that in today's lecture,"},{"startTime":3177.31,"endTime":3180.8,"body":"you've got a sense of the"},{"startTime":3177.31,"endTime":3180.8,"body":"richness of the many structures"},{"startTime":3180.8,"endTime":3184.02,"body":"in our universe, but I"},{"startTime":3180.8,"endTime":3184.02,"body":"hope at the same time,"},{"startTime":3184.02,"endTime":3187.88,"body":"you haven't just come away"},{"startTime":3184.02,"endTime":3187.88,"body":"with a sense of the richness"},{"startTime":3187.88,"endTime":3189.62,"body":"of the patterns of structure"},{"startTime":3189.62,"endTime":3193.33,"body":"in the sense of brightness"},{"startTime":3189.62,"endTime":3193.33,"body":"distributions and pretty spirals,"},{"startTime":3193.33,"endTime":3197.47,"body":"but also richness in"},{"startTime":3193.33,"endTime":3197.47,"body":"dynamical structure as well."},{"startTime":3197.47,"endTime":3199.038,"body":"Thank you very much."},{"startTime":3199.038,"endTime":3201.71,"body":"(audience applauding)"},{"startTime":3201.71,"endTime":3202.59,"body":"- So the first question is,"},{"startTime":3202.59,"endTime":3205.15,"body":"I was wondering if"},{"startTime":3202.59,"endTime":3205.15,"body":"galactic clusters flatten,"},{"startTime":3205.15,"endTime":3205.983,"body":"and if they do,"},{"startTime":3205.983,"endTime":3208.453,"body":"what is the mechanism that"},{"startTime":3205.983,"endTime":3208.453,"body":"causes them to flatten?"},{"startTime":3209.67,"endTime":3214.34,"body":"- Right, so why might"},{"startTime":3209.67,"endTime":3214.34,"body":"galactic clusters flatten?"},{"startTime":3214.34,"endTime":3216.98,"body":"Well, if you've got a rotating gas cloud,"},{"startTime":3216.98,"endTime":3219.71,"body":"and it forms stars and"},{"startTime":3216.98,"endTime":3219.71,"body":"all that sort of thing,"},{"startTime":3219.71,"endTime":3222.29,"body":"you might then find that under gravity,"},{"startTime":3222.29,"endTime":3224.53,"body":"or you will find that under gravity,"},{"startTime":3224.53,"endTime":3227.264,"body":"those stars will collapse into a disc"},{"startTime":3227.264,"endTime":3231.41,"body":"and that disc will be swirling"},{"startTime":3231.41,"endTime":3234.24,"body":"in accordance with the angular momentum"},{"startTime":3234.24,"endTime":3238.29,"body":"that the original gas cloud started with."},{"startTime":3238.29,"endTime":3240.22,"body":"Gravity will act in that direction"},{"startTime":3240.22,"endTime":3243.87,"body":"and the rotation will"},{"startTime":3240.22,"endTime":3243.87,"body":"continue within that disc."},{"startTime":3243.87,"endTime":3245.93,"body":"So the question is asking,"},{"startTime":3245.93,"endTime":3249.823,"body":"will you see clusters of"},{"startTime":3245.93,"endTime":3249.823,"body":"galaxies flatten in the same way?"},{"startTime":3250.74,"endTime":3253.52,"body":"And it's an interesting"},{"startTime":3250.74,"endTime":3253.52,"body":"question, because you might,"},{"startTime":3253.52,"endTime":3255.68,"body":"because flattening comes when you've got"},{"startTime":3256.69,"endTime":3260.51,"body":"collapse under gravity,"},{"startTime":3256.69,"endTime":3260.51,"body":"which isn't to a point,"},{"startTime":3260.51,"endTime":3265.01,"body":"because angular momentum"},{"startTime":3260.51,"endTime":3265.01,"body":"is offsetting the collapse"},{"startTime":3265.01,"endTime":3266.4,"body":"and just keeping the swirling,"},{"startTime":3266.4,"endTime":3269.6,"body":"the spiraling, the rotating ongoing."},{"startTime":3269.6,"endTime":3274.15,"body":"So you probably could"},{"startTime":3269.6,"endTime":3274.15,"body":"maybe pick up a signal"},{"startTime":3274.15,"endTime":3277.27,"body":"of the flattening of clusters of galaxies,"},{"startTime":3277.27,"endTime":3280.0,"body":"but probably what's a more dominant effect"},{"startTime":3280.0,"endTime":3285.0,"body":"is the original distribution"},{"startTime":3280.0,"endTime":3285.0,"body":"of gas throughout the universe."},{"startTime":3285.4,"endTime":3288.47,"body":"And we know that from that"},{"startTime":3285.4,"endTime":3288.47,"body":"very smooth starting point"},{"startTime":3288.47,"endTime":3291.04,"body":"that I mentioned at the"},{"startTime":3288.47,"endTime":3291.04,"body":"beginning of the lecture,"},{"startTime":3291.04,"endTime":3293.452,"body":"we know that it wasn't"},{"startTime":3291.04,"endTime":3293.452,"body":"smooth at all, but in fact,"},{"startTime":3293.452,"endTime":3296.44,"body":"as it collapses, sometimes it collapses"},{"startTime":3296.44,"endTime":3299.0,"body":"into really quite linear features."},{"startTime":3299.0,"endTime":3303.98,"body":"And I conjecture that predominantly"},{"startTime":3303.98,"endTime":3308.98,"body":"the shapes that clusters"},{"startTime":3303.98,"endTime":3308.98,"body":"of galaxies seem to span"},{"startTime":3310.82,"endTime":3313.63,"body":"will probably correspond a bit more"},{"startTime":3313.63,"endTime":3316.95,"body":"to the initial conditions"},{"startTime":3313.63,"endTime":3316.95,"body":"of the gas distribution"},{"startTime":3316.95,"endTime":3321.95,"body":"rather than at present to"},{"startTime":3316.95,"endTime":3321.95,"body":"any sort of local flattening"},{"startTime":3322.66,"endTime":3325.14,"body":"under gravity, but it would"},{"startTime":3322.66,"endTime":3325.14,"body":"be an interesting thing"},{"startTime":3325.14,"endTime":3327.06,"body":"to investigate, for sure."},{"startTime":3327.06,"endTime":3328.13,"body":"- Thank you."},{"startTime":3328.13,"endTime":3330.07,"body":"And a slightly broader question."},{"startTime":3330.07,"endTime":3331.98,"body":"Do you think that our"},{"startTime":3330.07,"endTime":3331.98,"body":"current climate change"},{"startTime":3331.98,"endTime":3334.59,"body":"could be due to the wobble in"},{"startTime":3331.98,"endTime":3334.59,"body":"the Earth's eccentric orbit"},{"startTime":3334.59,"endTime":3337.0,"body":"around the sun rather than CO2"},{"startTime":3337.0,"endTime":3340.29,"body":"as posited in a recent book on climate?"},{"startTime":3340.29,"endTime":3343.81,"body":"- So this question is"},{"startTime":3340.29,"endTime":3343.81,"body":"talking about the fact"},{"startTime":3343.81,"endTime":3347.86,"body":"that the orbit of the Earth around the sun"},{"startTime":3347.86,"endTime":3349.94,"body":"is not a perfect circle."},{"startTime":3349.94,"endTime":3353.01,"body":"It's, I mentioned 2/3 of"},{"startTime":3349.94,"endTime":3353.01,"body":"the way through my talk"},{"startTime":3353.01,"endTime":3355.22,"body":"that we don't just get circular orbits,"},{"startTime":3355.22,"endTime":3356.93,"body":"the ones that I showed in green,"},{"startTime":3356.93,"endTime":3358.65,"body":"but we get elliptical orbits,"},{"startTime":3358.65,"endTime":3361.37,"body":"the ones that are shown in blue."},{"startTime":3361.37,"endTime":3365.53,"body":"And Earth's orbit around the"},{"startTime":3361.37,"endTime":3365.53,"body":"sun is indeed elliptical."},{"startTime":3365.53,"endTime":3370.53,"body":"It has a non-zero eccentricity,"},{"startTime":3365.53,"endTime":3370.53,"body":"but it's not very eccentric."},{"startTime":3371.13,"endTime":3373.853,"body":"It's not very far from circular."},{"startTime":3374.89,"endTime":3379.723,"body":"And so modern thinking on"},{"startTime":3374.89,"endTime":3379.723,"body":"the importance of that,"},{"startTime":3380.99,"endTime":3385.99,"body":"I think many researchers"},{"startTime":3380.99,"endTime":3385.99,"body":"throughout the world,"},{"startTime":3386.16,"endTime":3389.36,"body":"people who work in atmospheric physics"},{"startTime":3389.36,"endTime":3393.26,"body":"would say, again, that's a subtle effect"},{"startTime":3393.26,"endTime":3396.74,"body":"compared with thermodynamics."},{"startTime":3396.74,"endTime":3399.84,"body":"Thermodynamics is a very"},{"startTime":3396.74,"endTime":3399.84,"body":"well understood science"},{"startTime":3399.84,"endTime":3404.84,"body":"and the fact that we are"},{"startTime":3399.84,"endTime":3404.84,"body":"trapping more and more heat"},{"startTime":3407.64,"endTime":3409.26,"body":"in Earth's atmosphere"},{"startTime":3409.26,"endTime":3411.41,"body":"because we're changing"},{"startTime":3409.26,"endTime":3411.41,"body":"the chemical composition"},{"startTime":3411.41,"endTime":3416.24,"body":"of Earth's atmosphere by stuffing"},{"startTime":3411.41,"endTime":3416.24,"body":"in more diatomic molecules"},{"startTime":3416.24,"endTime":3421.24,"body":"like CO2, like NO2, like H2O,"},{"startTime":3421.36,"endTime":3423.9,"body":"the more diatomic molecules"},{"startTime":3421.36,"endTime":3423.9,"body":"that are up there,"},{"startTime":3423.9,"endTime":3428.22,"body":"the more they will trap"},{"startTime":3423.9,"endTime":3428.22,"body":"in infrared radiation,"},{"startTime":3428.22,"endTime":3430.923,"body":"that if it could be"},{"startTime":3428.22,"endTime":3430.923,"body":"released into outer space,"},{"startTime":3432.66,"endTime":3436.19,"body":"and thereby cool down Earth's atmosphere,"},{"startTime":3436.19,"endTime":3439.61,"body":"you're having a big change"},{"startTime":3436.19,"endTime":3439.61,"body":"on the thermal nature"},{"startTime":3439.61,"endTime":3441.15,"body":"of our atmosphere."},{"startTime":3441.15,"endTime":3443.26,"body":"You're basically putting a big winter coat"},{"startTime":3444.55,"endTime":3446.81,"body":"on Earth's atmosphere."},{"startTime":3446.81,"endTime":3451.62,"body":"And that's the dominant effect"},{"startTime":3446.81,"endTime":3451.62,"body":"of why we're heating up."},{"startTime":3451.62,"endTime":3454.98,"body":"More diatomic molecules,"},{"startTime":3451.62,"endTime":3454.98,"body":"more CO2 in the atmosphere."},{"startTime":3454.98,"endTime":3457.7,"body":"It will get hot, it's"},{"startTime":3454.98,"endTime":3457.7,"body":"basic thermodynamics,"},{"startTime":3457.7,"endTime":3462.7,"body":"it's akin to the fact"},{"startTime":3457.7,"endTime":3462.7,"body":"that a greenhouse gets hot"},{"startTime":3464.95,"endTime":3467.21,"body":"when it's got summer sun irradiating on it"},{"startTime":3467.21,"endTime":3470.7,"body":"because infrared radiation can't escape"},{"startTime":3470.7,"endTime":3475.08,"body":"is a precise metaphor for what's going on."},{"startTime":3475.08,"endTime":3476.97,"body":"So I think that really dominates"},{"startTime":3476.97,"endTime":3481.34,"body":"over any relatively subtle"},{"startTime":3476.97,"endTime":3481.34,"body":"effects in the orbit of Earth"},{"startTime":3481.34,"endTime":3486.34,"body":"and, indeed, any subtle"},{"startTime":3481.34,"endTime":3486.34,"body":"variations in its eccentricity."},{"startTime":3486.84,"endTime":3489.31,"body":"I think they're pretty mild in comparison."},{"startTime":3489.31,"endTime":3490.143,"body":"- [Student] Thank you, professor."},{"startTime":3490.143,"endTime":3493.563,"body":"Could I ask something"},{"startTime":3490.143,"endTime":3493.563,"body":"about the blast wave?"},{"startTime":3494.78,"endTime":3498.11,"body":"I imagine a blast wave"},{"startTime":3494.78,"endTime":3498.11,"body":"being an enlarging sphere,"},{"startTime":3498.11,"endTime":3499.92,"body":"which it looked like at the beginning,"},{"startTime":3499.92,"endTime":3502.84,"body":"but very much not a sphere at the end."},{"startTime":3502.84,"endTime":3504.13,"body":"And was that something to do"},{"startTime":3504.13,"endTime":3506.41,"body":"with where the sort of blast frontier"},{"startTime":3506.41,"endTime":3509.363,"body":"started causing the star formation?"},{"startTime":3511.88,"endTime":3513.47,"body":"- Indirectly."},{"startTime":3513.47,"endTime":3515.79,"body":"So you're absolutely right."},{"startTime":3515.79,"endTime":3519.64,"body":"One would expect that a blast wave"},{"startTime":3519.64,"endTime":3521.96,"body":"would be spherically symmetric"},{"startTime":3521.96,"endTime":3526.6,"body":"if the environment into"},{"startTime":3521.96,"endTime":3526.6,"body":"which it was expanding"},{"startTime":3526.6,"endTime":3529.61,"body":"was itself spherically symmetric,"},{"startTime":3529.61,"endTime":3533.11,"body":"or even uniform in extent."},{"startTime":3533.11,"endTime":3537.28,"body":"However, in the particular"},{"startTime":3533.11,"endTime":3537.28,"body":"case that we see here,"},{"startTime":3537.28,"endTime":3539.21,"body":"there's no doubt that the blast wave"},{"startTime":3539.21,"endTime":3543.7,"body":"that extended left right"},{"startTime":3539.21,"endTime":3543.7,"body":"as seen on the slide"},{"startTime":3543.7,"endTime":3546.91,"body":"encountered much more dense gas"},{"startTime":3548.387,"endTime":3552.55,"body":"than the part of the blast wave"},{"startTime":3548.387,"endTime":3552.55,"body":"that was extending up down."},{"startTime":3552.55,"endTime":3554.51,"body":"It looks at it from the fact that,"},{"startTime":3554.51,"endTime":3556.86,"body":"maybe there's a tiny bit of"},{"startTime":3554.51,"endTime":3556.86,"body":"star formation, I don't know,"},{"startTime":3556.86,"endTime":3560.45,"body":"or that's a hot pixel on the"},{"startTime":3556.86,"endTime":3560.45,"body":"image, I'm not exactly sure,"},{"startTime":3560.45,"endTime":3564.694,"body":"but essentially no star"},{"startTime":3560.45,"endTime":3564.694,"body":"formation is triggered up down."},{"startTime":3564.694,"endTime":3567.17,"body":"And so that tells you in that direction,"},{"startTime":3567.17,"endTime":3570.393,"body":"relative to the original"},{"startTime":3567.17,"endTime":3570.393,"body":"sensor of the blast wave,"},{"startTime":3572.05,"endTime":3574.58,"body":"there was basically such a low density,"},{"startTime":3574.58,"endTime":3577.93,"body":"the blast wave went whoosh,"},{"startTime":3574.58,"endTime":3577.93,"body":"and didn't do any damage."},{"startTime":3577.93,"endTime":3581.81,"body":"Whereas left right, it"},{"startTime":3577.93,"endTime":3581.81,"body":"encountered loads of gas,"},{"startTime":3581.81,"endTime":3585.37,"body":"compressed it, it itself got slowed down."},{"startTime":3585.37,"endTime":3587.53,"body":"So being slowed down left right,"},{"startTime":3587.53,"endTime":3589.79,"body":"but able to speed up up down"},{"startTime":3589.79,"endTime":3592.623,"body":"gives you that somewhat rectangular shape."},{"startTime":3595.0,"endTime":3597.07,"body":"- Thank you, I'm afraid we're"},{"startTime":3595.0,"endTime":3597.07,"body":"probably going to have to draw"},{"startTime":3597.07,"endTime":3598.93,"body":"to a close at this point."},{"startTime":3598.93,"endTime":3600.85,"body":"I wanted to thank professor Blundell"},{"startTime":3600.85,"endTime":3603.06,"body":"and to thank you all for coming,"},{"startTime":3603.06,"endTime":3606.39,"body":"please note that her next"},{"startTime":3603.06,"endTime":3606.39,"body":"lecture will be on Wednesday,"},{"startTime":3606.39,"endTime":3611.11,"body":"the 23rd of February, and it"},{"startTime":3606.39,"endTime":3611.11,"body":"is on the Magnetic Universe."},{"startTime":3611.11,"endTime":3612.66,"body":"So please do join us for that."},{"startTime":3612.66,"endTime":3614.61,"body":"And please join me in"},{"startTime":3612.66,"endTime":3614.61,"body":"thanking her once again"},{"startTime":3614.61,"endTime":3616.25,"body":"for a fantastic lecture."},{"startTime":3616.25,"endTime":3618.942,"body":"(audience applauding)"}]}