{"version":"1.0.0","segments":[{"startTime":0.154,"endTime":2.987,"body":"(whooshing music)"},{"startTime":6.33,"endTime":9.18,"body":"- It's my pleasure to"},{"startTime":6.33,"endTime":9.18,"body":"talk to you this evening"},{"startTime":9.18,"endTime":12.72,"body":"about the end of massive stars."},{"startTime":12.72,"endTime":16.29,"body":"Massive stars are more"},{"startTime":12.72,"endTime":16.29,"body":"important for you and I"},{"startTime":16.29,"endTime":18.96,"body":"than you may first appreciate,"},{"startTime":18.96,"endTime":20.49,"body":"and that's because"},{"startTime":20.49,"endTime":25.26,"body":"if massive stars did"},{"startTime":20.49,"endTime":25.26,"body":"not evolve as they do,"},{"startTime":25.26,"endTime":29.91,"body":"and if massive stars"},{"startTime":25.26,"endTime":29.91,"body":"did not end as they do,"},{"startTime":29.91,"endTime":32.16,"body":"then we would not be here,"},{"startTime":32.16,"endTime":34.44,"body":"it's as simple as that."},{"startTime":34.44,"endTime":36.45,"body":"But let's begin tonight's lecture"},{"startTime":36.45,"endTime":39.63,"body":"by looking at this beautiful nebula."},{"startTime":39.63,"endTime":42.66,"body":"This is the Tarantula Nebula,"},{"startTime":42.66,"endTime":46.26,"body":"and it can be seen from"},{"startTime":42.66,"endTime":46.26,"body":"the Southern Hemisphere."},{"startTime":46.26,"endTime":49.83,"body":"It's as significant in"},{"startTime":46.26,"endTime":49.83,"body":"the Southern Hemisphere"},{"startTime":49.83,"endTime":52.11,"body":"as the Orion Nebula,"},{"startTime":52.11,"endTime":54.21,"body":"in the heart of the Orion constellation,"},{"startTime":54.21,"endTime":57.513,"body":"is to us here in the Northern Hemisphere."},{"startTime":58.83,"endTime":62.73,"body":"If this nebula were as close to Earth"},{"startTime":62.73,"endTime":66.03,"body":"as the Orion Nebula is to us,"},{"startTime":66.03,"endTime":70.71,"body":"it would be so bright that"},{"startTime":66.03,"endTime":70.71,"body":"it would cast shadows."},{"startTime":70.71,"endTime":71.543,"body":"But in fact,"},{"startTime":71.543,"endTime":75.81,"body":"the Tarantula Nebula is"},{"startTime":71.543,"endTime":75.81,"body":"not in our galaxy at all,"},{"startTime":75.81,"endTime":78.06,"body":"as the Orion Nebula is,"},{"startTime":78.06,"endTime":81.33,"body":"it's in a nearby galaxy."},{"startTime":81.33,"endTime":83.823,"body":"Let's zoom in and take a closer look."},{"startTime":84.66,"endTime":87.39,"body":"This is a particularly interesting nebula"},{"startTime":87.39,"endTime":89.04,"body":"because it's the site"},{"startTime":89.04,"endTime":94.04,"body":"of one of the most active"},{"startTime":89.04,"endTime":94.04,"body":"regions of ongoing star formation"},{"startTime":94.5,"endTime":96.3,"body":"that we can view,"},{"startTime":96.3,"endTime":97.133,"body":"and as I said,"},{"startTime":97.133,"endTime":100.71,"body":"it's immensely luminous"},{"startTime":97.133,"endTime":100.71,"body":"because of that activity,"},{"startTime":100.71,"endTime":103.11,"body":"if it were any closer to us,"},{"startTime":103.11,"endTime":106.89,"body":"it would really be a very"},{"startTime":103.11,"endTime":106.89,"body":"dominant source of brightness"},{"startTime":106.89,"endTime":108.543,"body":"in the night sky."},{"startTime":110.31,"endTime":114.12,"body":"The Tarantula Nebula is a favorite target"},{"startTime":114.12,"endTime":117.63,"body":"of the students at my"},{"startTime":114.12,"endTime":117.63,"body":"Chile school observatory,"},{"startTime":117.63,"endTime":121.29,"body":"where this image was taken."},{"startTime":121.29,"endTime":122.76,"body":"This is a picture of us"},{"startTime":122.76,"endTime":125.88,"body":"huddled in the cold of"},{"startTime":122.76,"endTime":125.88,"body":"the Chile observatory."},{"startTime":125.88,"endTime":129.03,"body":"I was thrilled to be able to"},{"startTime":125.88,"endTime":129.03,"body":"visit there last year again"},{"startTime":129.03,"endTime":132.963,"body":"after rather a long break due to lockdown."},{"startTime":134.07,"endTime":136.86,"body":"It is a favorite target"},{"startTime":134.07,"endTime":136.86,"body":"there for a good reason,"},{"startTime":136.86,"endTime":139.653,"body":"it's because it's a beautiful object,"},{"startTime":140.79,"endTime":145.02,"body":"but it's a significant object"},{"startTime":140.79,"endTime":145.02,"body":"for our lecture tonight"},{"startTime":145.02,"endTime":147.42,"body":"because of its recent history"},{"startTime":147.42,"endTime":151.2,"body":"and its recent contribution"},{"startTime":147.42,"endTime":151.2,"body":"to something very important"},{"startTime":151.2,"endTime":156.2,"body":"that happened 36 years ago, next month."},{"startTime":156.33,"endTime":158.553,"body":"What I've done now is to zoom out,"},{"startTime":159.57,"endTime":162.18,"body":"this is still a very"},{"startTime":159.57,"endTime":162.18,"body":"similar region of sky,"},{"startTime":162.18,"endTime":165.903,"body":"the Tarantula Nebula is"},{"startTime":162.18,"endTime":165.903,"body":"at the top of this slide,"},{"startTime":167.13,"endTime":171.753,"body":"still an image taken at my"},{"startTime":167.13,"endTime":171.753,"body":"Chile school observatory."},{"startTime":173.43,"endTime":176.07,"body":"Where the pink arrow is pointing"},{"startTime":176.07,"endTime":178.98,"body":"is the site of a very exciting event"},{"startTime":178.98,"endTime":183.69,"body":"that happened in February of 1987."},{"startTime":183.69,"endTime":187.752,"body":"I'm going to show you a"},{"startTime":183.69,"endTime":187.752,"body":"before and an after image"},{"startTime":187.752,"endTime":190.47,"body":"of that region of sky."},{"startTime":190.47,"endTime":193.47,"body":"Apologies for the 1980s font there,"},{"startTime":193.47,"endTime":195.81,"body":"but where that arrow is pointing"},{"startTime":195.81,"endTime":200.22,"body":"is the site of what was, prior to 1987,"},{"startTime":200.22,"endTime":203.43,"body":"a reasonably unremarkable star,"},{"startTime":203.43,"endTime":208.43,"body":"and this is after that star"},{"startTime":203.43,"endTime":208.43,"body":"underwent a supernova explosion."},{"startTime":209.94,"endTime":213.84,"body":"That star that the arrow"},{"startTime":209.94,"endTime":213.84,"body":"is pointing to on the left"},{"startTime":213.84,"endTime":216.36,"body":"ended its life with a bang,"},{"startTime":216.36,"endTime":219.33,"body":"it underwent a supernova explosion,"},{"startTime":219.33,"endTime":221.64,"body":"and I'm going to be addressing tonight"},{"startTime":221.64,"endTime":223.89,"body":"how that point is reached"},{"startTime":223.89,"endTime":228.093,"body":"and its significance for"},{"startTime":223.89,"endTime":228.093,"body":"us as humans here on Earth."},{"startTime":229.14,"endTime":233.67,"body":"I can't overstate how exciting"},{"startTime":229.14,"endTime":233.67,"body":"an event that was in 1987."},{"startTime":235.11,"endTime":238.2,"body":"I wasn't scientifically"},{"startTime":235.11,"endTime":238.2,"body":"sentient at the time,"},{"startTime":238.2,"endTime":240.42,"body":"but lots of other people were,"},{"startTime":240.42,"endTime":243.0,"body":"and I want to share with you a fax,"},{"startTime":243.0,"endTime":246.18,"body":"yes, really, a fax, not an email,"},{"startTime":246.18,"endTime":250.44,"body":"sent between two physicists,"},{"startTime":246.18,"endTime":250.44,"body":"two neutrino physicists,"},{"startTime":250.44,"endTime":253.63,"body":"trying to do astronomy with neutrinos"},{"startTime":254.49,"endTime":256.53,"body":"around the time that that happened."},{"startTime":256.53,"endTime":258.45,"body":"Neutrinos, by the way,"},{"startTime":258.45,"endTime":263.45,"body":"are particles that are"},{"startTime":258.45,"endTime":263.45,"body":"important in particle physics,"},{"startTime":264.0,"endTime":266.37,"body":"but they're very, very slippery,"},{"startTime":266.37,"endTime":269.55,"body":"it's very hard to detect them,"},{"startTime":269.55,"endTime":272.1,"body":"but they've been"},{"startTime":269.55,"endTime":272.1,"body":"conjectured, for a long time,"},{"startTime":272.1,"endTime":277.1,"body":"to be very important actors"},{"startTime":272.1,"endTime":277.1,"body":"in the supernova experience."},{"startTime":277.83,"endTime":278.73,"body":"So anyway,"},{"startTime":278.73,"endTime":283.207,"body":"here is a message written by"},{"startTime":278.73,"endTime":283.207,"body":"Sid Bludman to Eugene Beier:"},{"startTime":283.207,"endTime":285.367,"body":"\"Sensational news!"},{"startTime":285.367,"endTime":288.637,"body":"\"Supernova went off four to seven days ago"},{"startTime":288.637,"endTime":290.94,"body":"\"in the Large Magellanic Cloud.\""},{"startTime":290.94,"endTime":292.56,"body":"The Large Magellanic Cloud"},{"startTime":292.56,"endTime":295.23,"body":"is a galaxy nearby to the Milky Way"},{"startTime":295.23,"endTime":298.173,"body":"that contains the Tarantula Nebula,"},{"startTime":300.03,"endTime":302.82,"body":"so it's about 50 kiloparsecs away,"},{"startTime":302.82,"endTime":305.073,"body":"so a modest distance."},{"startTime":306.127,"endTime":308.317,"body":"\"Now, visible magnitude is four to five,"},{"startTime":308.317,"endTime":312.127,"body":"\"will reach maximum"},{"startTime":308.317,"endTime":312.127,"body":"magnitude between -1 and 0"},{"startTime":312.127,"endTime":313.507,"body":"\"in about week."},{"startTime":313.507,"endTime":315.637,"body":"\"Can you see it?\""},{"startTime":315.637,"endTime":320.637,"body":"\"This is what we have been"},{"startTime":315.637,"endTime":320.637,"body":"waiting 350 years for!\""},{"startTime":322.44,"endTime":327.44,"body":"Anyone who thinks that a"},{"startTime":322.44,"endTime":327.44,"body":"scientist is a brain on two legs"},{"startTime":327.57,"endTime":330.39,"body":"is significantly misinformed."},{"startTime":330.39,"endTime":333.09,"body":"Without the passion and the excitement"},{"startTime":333.09,"endTime":337.11,"body":"that come from engaging in"},{"startTime":333.09,"endTime":337.11,"body":"the spectacular phenomena"},{"startTime":337.11,"endTime":338.82,"body":"of the natural world,"},{"startTime":338.82,"endTime":341.19,"body":"you don't necessarily get the drive"},{"startTime":341.19,"endTime":343.65,"body":"to realize clever experiments"},{"startTime":343.65,"endTime":347.223,"body":"that enable us to understand"},{"startTime":343.65,"endTime":347.223,"body":"more about the natural world."},{"startTime":348.18,"endTime":350.13,"body":"This question, \"Can you see it?\""},{"startTime":350.13,"endTime":355.13,"body":"is asking, can you see"},{"startTime":350.13,"endTime":355.13,"body":"a signal in neutrinos?"},{"startTime":355.83,"endTime":357.9,"body":"Forget seeing it in light,"},{"startTime":357.9,"endTime":359.49,"body":"people in the Southern Hemisphere"},{"startTime":359.49,"endTime":364.49,"body":"were excitedly observing"},{"startTime":359.49,"endTime":364.49,"body":"it in the southern sky,"},{"startTime":364.92,"endTime":366.63,"body":"but Sid is asking Eugene,"},{"startTime":366.63,"endTime":368.853,"body":"can you see it in neutrinos?"},{"startTime":371.58,"endTime":375.0,"body":"Eugene Beier works on a"},{"startTime":371.58,"endTime":375.0,"body":"particle physics experiment,"},{"startTime":375.0,"endTime":377.52,"body":"or worked on a particle physics experiment"},{"startTime":377.52,"endTime":378.99,"body":"called Kamiokande,"},{"startTime":378.99,"endTime":381.57,"body":"and so he looked at the data."},{"startTime":381.57,"endTime":385.41,"body":"This is how you looked"},{"startTime":381.57,"endTime":385.41,"body":"at data in the 1980s."},{"startTime":385.41,"endTime":387.96,"body":"And for anyone who can't quite see"},{"startTime":387.96,"endTime":391.05,"body":"the trace of counts in"},{"startTime":387.96,"endTime":391.05,"body":"line with the finger there,"},{"startTime":391.05,"endTime":393.27,"body":"let me just zoom in."},{"startTime":393.27,"endTime":396.0,"body":"That spectacular explosion"},{"startTime":396.0,"endTime":400.74,"body":"corresponded to a handful"},{"startTime":396.0,"endTime":400.74,"body":"of counts in neutrinos,"},{"startTime":400.74,"endTime":403.77,"body":"some of them having"},{"startTime":400.74,"endTime":403.77,"body":"passed through the Earth"},{"startTime":403.77,"endTime":407.1,"body":"en route to the neutrino detector,"},{"startTime":407.1,"endTime":409.65,"body":"so this was an absolute triumph."},{"startTime":409.65,"endTime":411.84,"body":"It was utterly exciting"},{"startTime":411.84,"endTime":414.87,"body":"because had neutrinos been demonstrated"},{"startTime":414.87,"endTime":418.5,"body":"to not be a player in"},{"startTime":414.87,"endTime":418.5,"body":"supernova explosions,"},{"startTime":418.5,"endTime":420.33,"body":"it would have been a big puzzle,"},{"startTime":420.33,"endTime":423.63,"body":"and we would have understood"},{"startTime":420.33,"endTime":423.63,"body":"a lot less about about them"},{"startTime":423.63,"endTime":425.913,"body":"than we had dared to think that we do."},{"startTime":427.29,"endTime":429.51,"body":"So let's park neutrinos for a moment"},{"startTime":429.51,"endTime":434.07,"body":"and think about what will"},{"startTime":429.51,"endTime":434.07,"body":"make a star go supernova."},{"startTime":434.07,"endTime":437.01,"body":"Will all stars go bang at"},{"startTime":434.07,"endTime":437.01,"body":"the end of their lives?"},{"startTime":437.01,"endTime":439.2,"body":"Well, absolutely not,"},{"startTime":439.2,"endTime":441.69,"body":"and in fact, in the first"},{"startTime":439.2,"endTime":441.69,"body":"lecture in this series,"},{"startTime":441.69,"endTime":443.91,"body":"the one I gave before Christmas,"},{"startTime":443.91,"endTime":447.0,"body":"which was entitled \"The End of Our Sun,\""},{"startTime":447.0,"endTime":449.49,"body":"that was really a proxy"},{"startTime":447.0,"endTime":449.49,"body":"for the end of our sun"},{"startTime":449.49,"endTime":451.26,"body":"and stars like our sun,"},{"startTime":451.26,"endTime":455.34,"body":"stars with similar masses"},{"startTime":451.26,"endTime":455.34,"body":"to that of our sun,"},{"startTime":455.34,"endTime":459.66,"body":"they do not explode, they"},{"startTime":455.34,"endTime":459.66,"body":"do not end with a bang,"},{"startTime":459.66,"endTime":462.57,"body":"they expand and they expand as red giants,"},{"startTime":462.57,"endTime":466.11,"body":"the inner core collapses as a white dwarf,"},{"startTime":466.11,"endTime":468.6,"body":"comparatively quiescent"},{"startTime":468.6,"endTime":473.01,"body":"compared with the massive star endings"},{"startTime":473.01,"endTime":475.86,"body":"that I'm going to be"},{"startTime":473.01,"endTime":475.86,"body":"speaking about tonight."},{"startTime":475.86,"endTime":479.22,"body":"So it's only if you've got a massive star"},{"startTime":479.22,"endTime":484.22,"body":"that you stand a chance of"},{"startTime":479.22,"endTime":484.22,"body":"exploding as a supernova."},{"startTime":484.38,"endTime":487.41,"body":"Massive here means something like"},{"startTime":487.41,"endTime":489.24,"body":"eight times the mass of our sun,"},{"startTime":489.24,"endTime":493.473,"body":"or 10 times the mass of"},{"startTime":489.24,"endTime":493.473,"body":"our sun, or larger still."},{"startTime":494.85,"endTime":497.04,"body":"The mass of a star is,"},{"startTime":497.04,"endTime":499.74,"body":"as we'll see a little"},{"startTime":497.04,"endTime":499.74,"body":"later in the lecture,"},{"startTime":499.74,"endTime":502.92,"body":"turns out to be a very crucial property"},{"startTime":502.92,"endTime":507.75,"body":"for determining the evolution"},{"startTime":502.92,"endTime":507.75,"body":"and the ending of a star,"},{"startTime":507.75,"endTime":511.29,"body":"mass really calls the shots with stars."},{"startTime":511.29,"endTime":512.7,"body":"So let's consider the question"},{"startTime":512.7,"endTime":516.33,"body":"how rare are massive stars?"},{"startTime":516.33,"endTime":518.76,"body":"Massive stars are really quite rare"},{"startTime":518.76,"endTime":523.76,"body":"because they're less likely"},{"startTime":518.76,"endTime":523.76,"body":"to form in the first place."},{"startTime":524.46,"endTime":525.39,"body":"Stars form,"},{"startTime":525.39,"endTime":529.35,"body":"as I explained at the beginning"},{"startTime":525.39,"endTime":529.35,"body":"of my previous lecture,"},{"startTime":529.35,"endTime":534.24,"body":"by the collapse of gas clouds"},{"startTime":529.35,"endTime":534.24,"body":"under the action of gravity."},{"startTime":534.24,"endTime":537.42,"body":"When the gas has collapsed"},{"startTime":534.24,"endTime":537.42,"body":"and become very dense,"},{"startTime":537.42,"endTime":538.89,"body":"and even more dense,"},{"startTime":538.89,"endTime":543.3,"body":"and got hot enough for"},{"startTime":538.89,"endTime":543.3,"body":"fusion to take place,"},{"startTime":543.3,"endTime":546.87,"body":"once the process of"},{"startTime":543.3,"endTime":546.87,"body":"nuclear fusion is underway,"},{"startTime":546.87,"endTime":548.613,"body":"then you have a star."},{"startTime":551.28,"endTime":553.05,"body":"You will get a more massive star"},{"startTime":553.05,"endTime":555.87,"body":"if you've got a more massive gas cloud"},{"startTime":555.87,"endTime":558.63,"body":"that collapses to form a single star"},{"startTime":558.63,"endTime":561.57,"body":"and doesn't fragment"},{"startTime":558.63,"endTime":561.57,"body":"into a couple of stars,"},{"startTime":561.57,"endTime":563.43,"body":"or three or four stars."},{"startTime":563.43,"endTime":565.83,"body":"So getting a really massive star"},{"startTime":565.83,"endTime":568.26,"body":"does require the initial conditions"},{"startTime":568.26,"endTime":571.17,"body":"to be reasonably favorable,"},{"startTime":571.17,"endTime":572.73,"body":"but they're certainly out there,"},{"startTime":572.73,"endTime":574.59,"body":"and massive stars are a thing,"},{"startTime":574.59,"endTime":579.59,"body":"but probably, massive stars"},{"startTime":574.59,"endTime":579.59,"body":"are at most 1% of all stars"},{"startTime":581.16,"endTime":583.74,"body":"in the Milky Way Galaxy."},{"startTime":583.74,"endTime":588.74,"body":"So 1% reduces our numbers"},{"startTime":583.74,"endTime":588.74,"body":"of the supernova explosions"},{"startTime":589.14,"endTime":590.43,"body":"that we're likely to get,"},{"startTime":590.43,"endTime":592.203,"body":"but 1% isn't too bad."},{"startTime":593.55,"endTime":597.21,"body":"If you've got one of these"},{"startTime":593.55,"endTime":597.21,"body":"really massive stars,"},{"startTime":597.21,"endTime":599.79,"body":"then something else you"},{"startTime":597.21,"endTime":599.79,"body":"need to know about it"},{"startTime":599.79,"endTime":603.51,"body":"is that they live life fast and furious."},{"startTime":603.51,"endTime":605.43,"body":"The more massive a star is,"},{"startTime":605.43,"endTime":609.45,"body":"the more brief a star's life is,"},{"startTime":609.45,"endTime":612.12,"body":"it uses up all its fuel like the clappers,"},{"startTime":612.12,"endTime":613.53,"body":"and then it's gone,"},{"startTime":613.53,"endTime":614.88,"body":"with a bang, as we'll see,"},{"startTime":614.88,"endTime":616.44,"body":"but then it's gone."},{"startTime":616.44,"endTime":617.273,"body":"So the fact that,"},{"startTime":617.273,"endTime":621.6,"body":"even though you get 1%"},{"startTime":617.273,"endTime":621.6,"body":"of stars being massive,"},{"startTime":621.6,"endTime":626.34,"body":"the fact that they are visible"},{"startTime":621.6,"endTime":626.34,"body":"only much more fleetingly"},{"startTime":626.34,"endTime":629.55,"body":"than the much longer"},{"startTime":626.34,"endTime":629.55,"body":"lasting lower mass stars,"},{"startTime":629.55,"endTime":631.8,"body":"which are already more plentiful,"},{"startTime":631.8,"endTime":634.02,"body":"means that you're less likely to see"},{"startTime":634.02,"endTime":636.36,"body":"the activity and the excitement"},{"startTime":636.36,"endTime":639.48,"body":"of a big, massive galaxy."},{"startTime":639.48,"endTime":643.66,"body":"These monster stars run"},{"startTime":639.48,"endTime":643.66,"body":"out of fuel all too quickly"},{"startTime":645.78,"endTime":647.94,"body":"on a timescale much faster"},{"startTime":647.94,"endTime":650.82,"body":"than that taken for fusion to ignite"},{"startTime":650.82,"endTime":652.833,"body":"in the lower mass stars."},{"startTime":654.42,"endTime":657.27,"body":"So their lifetimes are much more fleeting,"},{"startTime":657.27,"endTime":660.03,"body":"that makes them much more rare,"},{"startTime":660.03,"endTime":661.29,"body":"but nonetheless,"},{"startTime":661.29,"endTime":664.47,"body":"when you look in any particular"},{"startTime":661.29,"endTime":664.47,"body":"direction in the sky,"},{"startTime":664.47,"endTime":666.18,"body":"and suppose we look at"},{"startTime":666.18,"endTime":670.11,"body":"this beautiful globular cluster of stars,"},{"startTime":670.11,"endTime":671.22,"body":"a cluster of stars"},{"startTime":671.22,"endTime":673.86,"body":"that's almost like its own little galaxy"},{"startTime":673.86,"endTime":675.48,"body":"within our galaxy,"},{"startTime":675.48,"endTime":679.26,"body":"this one is called Omega"},{"startTime":675.48,"endTime":679.26,"body":"Cen, Omega Centaurus,"},{"startTime":679.26,"endTime":680.82,"body":"also in the Southern Hemisphere,"},{"startTime":680.82,"endTime":683.82,"body":"and indeed visible to the naked eye,"},{"startTime":683.82,"endTime":688.143,"body":"you will find stars that"},{"startTime":683.82,"endTime":688.143,"body":"are interestingly massive."},{"startTime":689.4,"endTime":694.23,"body":"But the conditions here"},{"startTime":689.4,"endTime":694.23,"body":"in this cluster of stars"},{"startTime":694.23,"endTime":699.03,"body":"is so different from"},{"startTime":694.23,"endTime":699.03,"body":"our bit of the Milky Way"},{"startTime":699.03,"endTime":703.44,"body":"that stars tend to evolve a"},{"startTime":699.03,"endTime":703.44,"body":"little more differently anyway."},{"startTime":703.44,"endTime":708.09,"body":"The density of the stars"},{"startTime":703.44,"endTime":708.09,"body":"themselves is so crowded"},{"startTime":708.09,"endTime":710.82,"body":"that stars are only"},{"startTime":708.09,"endTime":710.82,"body":"separate from one another"},{"startTime":710.82,"endTime":714.0,"body":"by something like a light month."},{"startTime":714.0,"endTime":717.9,"body":"A light month is the"},{"startTime":714.0,"endTime":717.9,"body":"distance that light travels"},{"startTime":717.9,"endTime":719.28,"body":"in one month,"},{"startTime":719.28,"endTime":721.14,"body":"and by astronomical standards,"},{"startTime":721.14,"endTime":723.66,"body":"it's really pretty close."},{"startTime":723.66,"endTime":728.04,"body":"The nearest star to our"},{"startTime":723.66,"endTime":728.04,"body":"nearest star, the Sun,"},{"startTime":728.04,"endTime":730.2,"body":"is called Proxima Centauri,"},{"startTime":730.2,"endTime":733.47,"body":"and that is four light years away."},{"startTime":733.47,"endTime":736.14,"body":"It's probably a good thing"},{"startTime":733.47,"endTime":736.14,"body":"it's not vastly closer,"},{"startTime":736.14,"endTime":737.76,"body":"it is certainly a good thing"},{"startTime":737.76,"endTime":741.153,"body":"it is not merely one light month away."},{"startTime":742.14,"endTime":746.82,"body":"Life in a star in the center"},{"startTime":742.14,"endTime":746.82,"body":"of this globular cluster,"},{"startTime":746.82,"endTime":748.26,"body":"Omega Centauri,"},{"startTime":748.26,"endTime":749.793,"body":"would be pretty hectic."},{"startTime":751.41,"endTime":753.45,"body":"Here's another beautiful globular cluster,"},{"startTime":753.45,"endTime":755.94,"body":"this one is called Messier 22,"},{"startTime":755.94,"endTime":758.64,"body":"it's nearly 11,000 light years from Earth,"},{"startTime":758.64,"endTime":760.98,"body":"and again, it's got a distribution"},{"startTime":760.98,"endTime":764.97,"body":"of different masses of stars."},{"startTime":764.97,"endTime":766.32,"body":"Its spatial extent"},{"startTime":766.32,"endTime":770.373,"body":"is comparable with the"},{"startTime":766.32,"endTime":770.373,"body":"diameter of the full moon."},{"startTime":771.42,"endTime":773.73,"body":"One day, that Tarantula Nebula,"},{"startTime":773.73,"endTime":778.47,"body":"that gas cloud which is"},{"startTime":773.73,"endTime":778.47,"body":"collapsing under gravity"},{"startTime":778.47,"endTime":781.08,"body":"that I showed you at the"},{"startTime":778.47,"endTime":781.08,"body":"start of this lecture,"},{"startTime":781.08,"endTime":783.45,"body":"will look a bit like this."},{"startTime":783.45,"endTime":787.14,"body":"Already, the Tarantula"},{"startTime":783.45,"endTime":787.14,"body":"Nebula is forming stars,"},{"startTime":787.14,"endTime":789.3,"body":"but it's got a long journey to go on"},{"startTime":789.3,"endTime":794.3,"body":"of hundreds of millions of"},{"startTime":789.3,"endTime":794.3,"body":"years of forming more stars"},{"startTime":794.34,"endTime":797.31,"body":"until it's stars everywhere,"},{"startTime":797.31,"endTime":802.31,"body":"as we have in this"},{"startTime":797.31,"endTime":802.31,"body":"particular cluster of stars,"},{"startTime":802.32,"endTime":804.363,"body":"again in our galaxy."},{"startTime":805.86,"endTime":807.57,"body":"So how do stars evolve,"},{"startTime":807.57,"endTime":810.39,"body":"and how can we begin to"},{"startTime":807.57,"endTime":810.39,"body":"understand their behavior,"},{"startTime":810.39,"endTime":811.83,"body":"and how can we begin to think"},{"startTime":811.83,"endTime":815.913,"body":"in terms of how the mass"},{"startTime":811.83,"endTime":815.913,"body":"of stars changes with time?"},{"startTime":817.17,"endTime":820.53,"body":"Well, it turns out that the mass of a star"},{"startTime":820.53,"endTime":823.173,"body":"strongly influences its temperature."},{"startTime":824.01,"endTime":826.98,"body":"The more mass that a star has,"},{"startTime":826.98,"endTime":830.157,"body":"the more dense it will collapse to be,"},{"startTime":830.157,"endTime":834.66,"body":"and so the more heat"},{"startTime":830.157,"endTime":834.66,"body":"energy you can radiate."},{"startTime":834.66,"endTime":837.72,"body":"So how do we measure temperature in stars?"},{"startTime":837.72,"endTime":840.72,"body":"It turns out this is pretty easy to do."},{"startTime":840.72,"endTime":844.08,"body":"Stars manifestly come in different colors."},{"startTime":844.08,"endTime":847.23,"body":"Now, I don't know how"},{"startTime":844.08,"endTime":847.23,"body":"clear it is for you to see,"},{"startTime":847.23,"endTime":848.73,"body":"in this particular image,"},{"startTime":848.73,"endTime":851.04,"body":"that some stars are yellower than others,"},{"startTime":851.04,"endTime":853.35,"body":"some stars are bluer than others,"},{"startTime":853.35,"endTime":855.84,"body":"it turns out it's actually"},{"startTime":853.35,"endTime":855.84,"body":"easier to see this"},{"startTime":855.84,"endTime":858.15,"body":"if you de-focus the telescope,"},{"startTime":858.15,"endTime":861.123,"body":"and then you can see the"},{"startTime":858.15,"endTime":861.123,"body":"colors a bit more clearly."},{"startTime":862.68,"endTime":865.8,"body":"It's exactly the same field of view,"},{"startTime":865.8,"endTime":868.08,"body":"but stars come in different colors,"},{"startTime":868.08,"endTime":873.08,"body":"and color maps to temperature"},{"startTime":868.08,"endTime":873.08,"body":"in a very specific way."},{"startTime":874.26,"endTime":876.99,"body":"Now, for those among you who are thinking,"},{"startTime":876.99,"endTime":880.44,"body":"goodness, isn't color a bit subjective,"},{"startTime":880.44,"endTime":881.37,"body":"well, it may be"},{"startTime":881.37,"endTime":884.28,"body":"in the case of choosing"},{"startTime":881.37,"endTime":884.28,"body":"which item of clothing"},{"startTime":884.28,"endTime":886.86,"body":"goes with another item of clothing,"},{"startTime":886.86,"endTime":889.32,"body":"but it's not the case in astronomy"},{"startTime":889.32,"endTime":891.0,"body":"because in astronomy,"},{"startTime":891.0,"endTime":895.11,"body":"color is measurable, it is quantifiable,"},{"startTime":895.11,"endTime":896.61,"body":"and repeatedly so,"},{"startTime":896.61,"endTime":899.43,"body":"and it tells us about physics."},{"startTime":899.43,"endTime":900.57,"body":"If you think of a star"},{"startTime":900.57,"endTime":903.873,"body":"as a big ball of gas"},{"startTime":900.57,"endTime":903.873,"body":"undergoing nuclear fusion,"},{"startTime":905.19,"endTime":909.03,"body":"the color that it shows itself to be"},{"startTime":909.03,"endTime":912.423,"body":"arises from the spectrum of"},{"startTime":909.03,"endTime":912.423,"body":"light that we get from it,"},{"startTime":913.32,"endTime":917.64,"body":"and the temperature that"},{"startTime":913.32,"endTime":917.64,"body":"that ball of fusing gas is at"},{"startTime":917.64,"endTime":921.45,"body":"determines exactly where"},{"startTime":917.64,"endTime":921.45,"body":"that appears on the spectrum,"},{"startTime":921.45,"endTime":924.57,"body":"and hence what color it turns out to be."},{"startTime":924.57,"endTime":929.1,"body":"All bodies radiate in this way."},{"startTime":929.1,"endTime":929.97,"body":"Now, you may be thinking,"},{"startTime":929.97,"endTime":930.84,"body":"well hang on,"},{"startTime":930.84,"endTime":933.15,"body":"the colors that we're looking at"},{"startTime":933.15,"endTime":935.58,"body":"corresponding to the"},{"startTime":933.15,"endTime":935.58,"body":"clothes that we're wearing,"},{"startTime":935.58,"endTime":937.32,"body":"surely that's to do with the colors"},{"startTime":937.32,"endTime":939.78,"body":"that are radiating off the light bulbs,"},{"startTime":939.78,"endTime":941.46,"body":"according to the nature of the light bulb,"},{"startTime":941.46,"endTime":942.99,"body":"and according to the fabric"},{"startTime":942.99,"endTime":944.67,"body":"that our clothes are made out of,"},{"startTime":944.67,"endTime":947.58,"body":"sure, I completely agree with that,"},{"startTime":947.58,"endTime":951.45,"body":"but I'm talking about the"},{"startTime":947.58,"endTime":951.45,"body":"radiation that a body gives off"},{"startTime":951.45,"endTime":954.12,"body":"by virtue of its temperature."},{"startTime":954.12,"endTime":956.943,"body":"This is honestly the case for all bodies."},{"startTime":957.84,"endTime":959.19,"body":"Now, it's notable, isn't it,"},{"startTime":959.19,"endTime":961.83,"body":"that when we put the lights out at night,"},{"startTime":961.83,"endTime":962.91,"body":"we don't see anything,"},{"startTime":962.91,"endTime":965.28,"body":"we don't see the objects in our bedrooms."},{"startTime":965.28,"endTime":969.18,"body":"Well, you would if you got a"},{"startTime":965.28,"endTime":969.18,"body":"thermal infrared imaging camera"},{"startTime":969.18,"endTime":972.3,"body":"because they would be"},{"startTime":969.18,"endTime":972.3,"body":"radiating at 20 degrees,"},{"startTime":972.3,"endTime":975.393,"body":"or whatever temperature"},{"startTime":972.3,"endTime":975.393,"body":"our bedroom is set to."},{"startTime":976.47,"endTime":980.13,"body":"Which part of the spectrum"},{"startTime":976.47,"endTime":980.13,"body":"an object radiates at"},{"startTime":980.13,"endTime":983.04,"body":"depends on what its temperature is,"},{"startTime":983.04,"endTime":985.29,"body":"and so color gives us temperature,"},{"startTime":985.29,"endTime":987.51,"body":"and depending on what we're talking about,"},{"startTime":987.51,"endTime":990.27,"body":"we can totally tell what"},{"startTime":987.51,"endTime":990.27,"body":"temperature it's at."},{"startTime":990.27,"endTime":992.25,"body":"If we're talking about steel,"},{"startTime":992.25,"endTime":994.41,"body":"then a muted red color will tell us"},{"startTime":994.41,"endTime":997.47,"body":"that that steel is at about 600 degrees,"},{"startTime":997.47,"endTime":1000.29,"body":"if it's bright red,"},{"startTime":997.47,"endTime":1000.29,"body":"it's about 800 degrees,"},{"startTime":1000.29,"endTime":1002.78,"body":"if it's orange, it's 900 degrees,"},{"startTime":1002.78,"endTime":1005.24,"body":"if it's yellow, it's over 1,000 degrees,"},{"startTime":1005.24,"endTime":1007.91,"body":"and if it's white, it's"},{"startTime":1005.24,"endTime":1007.91,"body":"more like 1,300 degrees,"},{"startTime":1007.91,"endTime":1009.593,"body":"if we're talking about steel."},{"startTime":1011.51,"endTime":1013.49,"body":"Now, in thermodynamics,"},{"startTime":1013.49,"endTime":1017.0,"body":"when we talk about the"},{"startTime":1013.49,"endTime":1017.0,"body":"radiation from a body"},{"startTime":1017.0,"endTime":1020.3,"body":"because of the temperature that it's at,"},{"startTime":1020.3,"endTime":1022.1,"body":"we tend to think in terms of"},{"startTime":1022.1,"endTime":1026.136,"body":"what in thermodynamics"},{"startTime":1022.1,"endTime":1026.136,"body":"is called a black body,"},{"startTime":1026.136,"endTime":1029.06,"body":"a body that doesn't absorb"},{"startTime":1026.136,"endTime":1029.06,"body":"or emit preferentially"},{"startTime":1029.06,"endTime":1030.893,"body":"in terms of one particular color,"},{"startTime":1030.893,"endTime":1034.01,"body":"it's not to do with the light"},{"startTime":1030.893,"endTime":1034.01,"body":"bulb that's irradiating it,"},{"startTime":1034.01,"endTime":1036.263,"body":"it's all to do with temperature."},{"startTime":1037.1,"endTime":1040.49,"body":"If you ascribe a particular"},{"startTime":1037.1,"endTime":1040.49,"body":"temperature to a black body,"},{"startTime":1040.49,"endTime":1044.63,"body":"you've got a map for the"},{"startTime":1040.49,"endTime":1044.63,"body":"shape of the spectrum of light"},{"startTime":1044.63,"endTime":1045.89,"body":"that is emitted from it,"},{"startTime":1045.89,"endTime":1047.153,"body":"and hence its color."},{"startTime":1048.44,"endTime":1053.21,"body":"So here is an example of what"},{"startTime":1048.44,"endTime":1053.21,"body":"is known in thermodynamics"},{"startTime":1053.21,"endTime":1055.94,"body":"as the black body spectrum,"},{"startTime":1055.94,"endTime":1059.52,"body":"and you can see that the"},{"startTime":1055.94,"endTime":1059.52,"body":"spectrum shifts over a bit"},{"startTime":1060.56,"endTime":1062.3,"body":"into the visible part of the spectrum,"},{"startTime":1062.3,"endTime":1065.12,"body":"which is shown over here in pale gray,"},{"startTime":1065.12,"endTime":1068.663,"body":"only when the temperature of"},{"startTime":1065.12,"endTime":1068.663,"body":"that body gets hot enough."},{"startTime":1070.13,"endTime":1071.18,"body":"And so, immediately,"},{"startTime":1071.18,"endTime":1073.46,"body":"we can tell stars are very hot"},{"startTime":1073.46,"endTime":1076.52,"body":"because we see them in"},{"startTime":1073.46,"endTime":1076.52,"body":"the optical wave band"},{"startTime":1076.52,"endTime":1078.863,"body":"to which our eyes are sensitive."},{"startTime":1080.09,"endTime":1084.47,"body":"This is the view over my"},{"startTime":1080.09,"endTime":1084.47,"body":"house about 46, 45 hours ago."},{"startTime":1088.16,"endTime":1091.16,"body":"I have an all-sky camera"},{"startTime":1088.16,"endTime":1091.16,"body":"on the side of my house,"},{"startTime":1091.16,"endTime":1093.05,"body":"I have a very tolerant husband,"},{"startTime":1093.05,"endTime":1096.29,"body":"and you can perhaps even see already,"},{"startTime":1096.29,"endTime":1097.97,"body":"certainly if I zoom in,"},{"startTime":1097.97,"endTime":1102.56,"body":"that some of the stars are"},{"startTime":1097.97,"endTime":1102.56,"body":"slightly different colors."},{"startTime":1102.56,"endTime":1104.39,"body":"Thankfully, stars are at temperatures"},{"startTime":1104.39,"endTime":1106.58,"body":"where we can see them in the optical,"},{"startTime":1106.58,"endTime":1108.35,"body":"and I hope that maybe you recognize"},{"startTime":1108.35,"endTime":1110.72,"body":"this distribution of stars in the bottom"},{"startTime":1110.72,"endTime":1114.68,"body":"as our beloved Orion constellation,"},{"startTime":1114.68,"endTime":1117.86,"body":"and perhaps you can see the orange-red one"},{"startTime":1117.86,"endTime":1119.42,"body":"in the top-left corner,"},{"startTime":1119.42,"endTime":1120.98,"body":"that's Betelgeuse,"},{"startTime":1120.98,"endTime":1123.32,"body":"diametrically opposite which is Rigel,"},{"startTime":1123.32,"endTime":1125.07,"body":"which is rather more blue in color."},{"startTime":1126.35,"endTime":1128.12,"body":"Just that observation"},{"startTime":1128.12,"endTime":1131.33,"body":"from an all-sky camera"},{"startTime":1128.12,"endTime":1131.33,"body":"on the side of my house"},{"startTime":1131.33,"endTime":1133.1,"body":"on a cold winter's night"},{"startTime":1133.1,"endTime":1135.35,"body":"giving us different"},{"startTime":1133.1,"endTime":1135.35,"body":"colors for those two stars"},{"startTime":1135.35,"endTime":1138.56,"body":"immediately says they're"},{"startTime":1135.35,"endTime":1138.56,"body":"at a different temperature."},{"startTime":1138.56,"endTime":1142.46,"body":"If we split up the light into"},{"startTime":1138.56,"endTime":1142.46,"body":"a rainbow, into a spectrum,"},{"startTime":1142.46,"endTime":1143.81,"body":"we can see that Betelgeuse,"},{"startTime":1144.83,"endTime":1146.99,"body":"which was the orange one in the top-left,"},{"startTime":1146.99,"endTime":1148.67,"body":"has quite a bit of red light,"},{"startTime":1148.67,"endTime":1151.52,"body":"whereas Rigel, the one opposite,"},{"startTime":1151.52,"endTime":1154.79,"body":"has rather more blue-purple light."},{"startTime":1154.79,"endTime":1158.903,"body":"Rigel is distinctly"},{"startTime":1154.79,"endTime":1158.903,"body":"hotter than Betelgeuse."},{"startTime":1160.16,"endTime":1165.11,"body":"So looking at stars' colors"},{"startTime":1160.16,"endTime":1165.11,"body":"tells us about the temperature,"},{"startTime":1165.11,"endTime":1167.99,"body":"and that tells us where they are"},{"startTime":1167.99,"endTime":1170.6,"body":"in terms of their evolutionary state"},{"startTime":1170.6,"endTime":1172.193,"body":"and what their mass is."},{"startTime":1173.18,"endTime":1175.463,"body":"So let's draw ourselves"},{"startTime":1173.18,"endTime":1175.463,"body":"a temperature scale."},{"startTime":1176.51,"endTime":1179.0,"body":"The coolest stars you will ever see"},{"startTime":1179.0,"endTime":1182.09,"body":"are a couple of thousand degrees,"},{"startTime":1182.09,"endTime":1184.73,"body":"and the reason why we have"},{"startTime":1182.09,"endTime":1184.73,"body":"that minimum there is,"},{"startTime":1184.73,"endTime":1186.38,"body":"a star is only a star"},{"startTime":1186.38,"endTime":1190.4,"body":"if the condensed gas cloud"},{"startTime":1186.38,"endTime":1190.4,"body":"is sufficiently massive"},{"startTime":1190.4,"endTime":1193.88,"body":"that it could collapse"},{"startTime":1190.4,"endTime":1193.88,"body":"sufficiently under gravity,"},{"startTime":1193.88,"endTime":1195.62,"body":"that the densities were high enough,"},{"startTime":1195.62,"endTime":1197.42,"body":"that the temperatures were high enough"},{"startTime":1197.42,"endTime":1201.86,"body":"for nuclear fusion"},{"startTime":1197.42,"endTime":1201.86,"body":"reactions to take place."},{"startTime":1201.86,"endTime":1203.48,"body":"At much higher temperatures,"},{"startTime":1203.48,"endTime":1206.33,"body":"we see much bluer stars."},{"startTime":1206.33,"endTime":1209.57,"body":"And so, already, we can see,"},{"startTime":1209.57,"endTime":1211.31,"body":"we can probably work out"},{"startTime":1211.31,"endTime":1213.68,"body":"what the distribution of temperatures is"},{"startTime":1213.68,"endTime":1216.23,"body":"for the stars in this image,"},{"startTime":1216.23,"endTime":1219.65,"body":"which, incidentally, is"},{"startTime":1216.23,"endTime":1219.65,"body":"also of Omega Centauri,"},{"startTime":1219.65,"endTime":1224.093,"body":"but imaged by the Hubble Space"},{"startTime":1219.65,"endTime":1224.093,"body":"Telescope, operated by NASA."},{"startTime":1225.14,"endTime":1226.31,"body":"So we can see"},{"startTime":1226.31,"endTime":1228.26,"body":"that the blue ones are going"},{"startTime":1226.31,"endTime":1228.26,"body":"to be a whole lot hotter"},{"startTime":1228.26,"endTime":1229.093,"body":"than the red ones,"},{"startTime":1229.093,"endTime":1231.383,"body":"and the white ones are"},{"startTime":1229.093,"endTime":1231.383,"body":"somewhere in between."},{"startTime":1232.73,"endTime":1236.03,"body":"So as we look at this,"},{"startTime":1236.03,"endTime":1239.0,"body":"if we now rearrange those stars,"},{"startTime":1239.0,"endTime":1242.51,"body":"thanks to a very helpful"},{"startTime":1239.0,"endTime":1242.51,"body":"visualization by NASA,"},{"startTime":1242.51,"endTime":1246.47,"body":"not changing the spatial"},{"startTime":1242.51,"endTime":1246.47,"body":"distribution at all,"},{"startTime":1246.47,"endTime":1250.01,"body":"but just ordering them left"},{"startTime":1246.47,"endTime":1250.01,"body":"right in terms of color,"},{"startTime":1250.01,"endTime":1255.01,"body":"so bluest blue on the left"},{"startTime":1250.01,"endTime":1255.01,"body":"and reddest red on the right,"},{"startTime":1255.35,"endTime":1256.183,"body":"we can see"},{"startTime":1256.183,"endTime":1260.33,"body":"that we've got something of a"},{"startTime":1256.183,"endTime":1260.33,"body":"striking distribution already."},{"startTime":1260.33,"endTime":1263.39,"body":"The bluest stars, the hottest stars,"},{"startTime":1263.39,"endTime":1264.56,"body":"spoiler alert,"},{"startTime":1264.56,"endTime":1268.403,"body":"the most massive stars are"},{"startTime":1264.56,"endTime":1268.403,"body":"relatively few in number,"},{"startTime":1269.39,"endTime":1271.94,"body":"there are truckloads of"},{"startTime":1269.39,"endTime":1271.94,"body":"the white and yellow ones"},{"startTime":1271.94,"endTime":1272.84,"body":"in the middle,"},{"startTime":1272.84,"endTime":1274.64,"body":"and again, the red ones,"},{"startTime":1274.64,"endTime":1276.65,"body":"on the extreme cool side,"},{"startTime":1276.65,"endTime":1278.663,"body":"are relatively few in number."},{"startTime":1279.74,"endTime":1283.61,"body":"So we've got temperature"},{"startTime":1279.74,"endTime":1283.61,"body":"increasing from right to left,"},{"startTime":1283.61,"endTime":1286.1,"body":"a somewhat unusual way round,"},{"startTime":1286.1,"endTime":1288.41,"body":"but now let's build up this graph further"},{"startTime":1288.41,"endTime":1292.28,"body":"and think about how the luminosity,"},{"startTime":1292.28,"endTime":1295.85,"body":"that is to say the intrinsic"},{"startTime":1292.28,"endTime":1295.85,"body":"brightness of a star,"},{"startTime":1295.85,"endTime":1299.99,"body":"the rate at which it puts"},{"startTime":1295.85,"endTime":1299.99,"body":"out energy every second,"},{"startTime":1299.99,"endTime":1304.07,"body":"let's see what happens if we"},{"startTime":1299.99,"endTime":1304.07,"body":"now order the stars vertically"},{"startTime":1304.07,"endTime":1307.16,"body":"according to how luminous they are."},{"startTime":1307.16,"endTime":1311.21,"body":"So, these are the axes"},{"startTime":1307.16,"endTime":1311.21,"body":"that I'm going to be using,"},{"startTime":1311.21,"endTime":1313.49,"body":"and when we do rearrange the stars,"},{"startTime":1313.49,"endTime":1316.31,"body":"I hope that you'll see, very clearly,"},{"startTime":1316.31,"endTime":1317.75,"body":"a distribution of stars"},{"startTime":1317.75,"endTime":1321.68,"body":"with a diagonal stripe"},{"startTime":1317.75,"endTime":1321.68,"body":"going all the way across,"},{"startTime":1321.68,"endTime":1325.28,"body":"which is known as the"},{"startTime":1321.68,"endTime":1325.28,"body":"main sequence of stars,"},{"startTime":1325.28,"endTime":1328.16,"body":"it's where normally operating stars"},{"startTime":1328.16,"endTime":1330.2,"body":"who are following the instruction manual"},{"startTime":1330.2,"endTime":1332.15,"body":"and undergoing nuclear fusion"},{"startTime":1332.15,"endTime":1333.5,"body":"are to be found."},{"startTime":1333.5,"endTime":1335.99,"body":"So remember that diagonal line"},{"startTime":1335.99,"endTime":1338.72,"body":"and remember luminosity going up."},{"startTime":1338.72,"endTime":1342.5,"body":"So let's go back to the"},{"startTime":1338.72,"endTime":1342.5,"body":"distribution of stars"},{"startTime":1342.5,"endTime":1344.81,"body":"that we had just sorted in color now,"},{"startTime":1344.81,"endTime":1347.75,"body":"which is equivalent to"},{"startTime":1344.81,"endTime":1347.75,"body":"sorting in temperature,"},{"startTime":1347.75,"endTime":1351.56,"body":"and let's allow that to play out."},{"startTime":1351.56,"endTime":1354.98,"body":"So the most luminous"},{"startTime":1351.56,"endTime":1354.98,"body":"stars going to the top,"},{"startTime":1354.98,"endTime":1357.89,"body":"oh look, all the blue"},{"startTime":1354.98,"endTime":1357.89,"body":"ones are going to the top,"},{"startTime":1357.89,"endTime":1361.37,"body":"and we've got a diagonal stripe down here"},{"startTime":1361.37,"endTime":1364.85,"body":"corresponding to the"},{"startTime":1361.37,"endTime":1364.85,"body":"main sequence of stars."},{"startTime":1364.85,"endTime":1368.03,"body":"So although this particular diagram"},{"startTime":1368.03,"endTime":1370.94,"body":"is only for the stars in that image"},{"startTime":1370.94,"endTime":1374.453,"body":"of a small region of"},{"startTime":1370.94,"endTime":1374.453,"body":"the Omega Cen cluster,"},{"startTime":1375.32,"endTime":1378.26,"body":"if our sun were to be"},{"startTime":1375.32,"endTime":1378.26,"body":"included on this graph,"},{"startTime":1378.26,"endTime":1380.72,"body":"it would be just in the white region,"},{"startTime":1380.72,"endTime":1382.643,"body":"on the main sequence just there."},{"startTime":1383.66,"endTime":1385.76,"body":"So if a star is on the main sequence,"},{"startTime":1385.76,"endTime":1388.553,"body":"it's undergoing normal nuclear fusion."},{"startTime":1389.57,"endTime":1391.79,"body":"If we could wind the clock back"},{"startTime":1391.79,"endTime":1396.79,"body":"and look at this graph for the"},{"startTime":1391.79,"endTime":1396.79,"body":"Omega Cen cluster in the past"},{"startTime":1397.43,"endTime":1400.85,"body":"all you would see would"},{"startTime":1397.43,"endTime":1400.85,"body":"be a single diagonal"},{"startTime":1400.85,"endTime":1404.63,"body":"going from the bottom-right"},{"startTime":1400.85,"endTime":1404.63,"body":"up to the top-left."},{"startTime":1404.63,"endTime":1406.37,"body":"But the stars that have deviated"},{"startTime":1406.37,"endTime":1409.25,"body":"and drifted off this main sequence"},{"startTime":1409.25,"endTime":1414.25,"body":"are those that are entering"},{"startTime":1409.25,"endTime":1414.25,"body":"the ending of their lives,"},{"startTime":1414.29,"endTime":1415.64,"body":"to an extent."},{"startTime":1415.64,"endTime":1419.36,"body":"So for example, in this"},{"startTime":1415.64,"endTime":1419.36,"body":"top-right corner here,"},{"startTime":1419.36,"endTime":1422.0,"body":"so this is relatively cool stars,"},{"startTime":1422.0,"endTime":1424.49,"body":"but really quite luminous,"},{"startTime":1424.49,"endTime":1425.75,"body":"that already tells you"},{"startTime":1425.75,"endTime":1428.72,"body":"that they've got to be"},{"startTime":1425.75,"endTime":1428.72,"body":"really quite big stars"},{"startTime":1428.72,"endTime":1431.36,"body":"because you've got to"},{"startTime":1428.72,"endTime":1431.36,"body":"have quite a lot of stuff"},{"startTime":1431.36,"endTime":1435.2,"body":"if you're going to radiate"},{"startTime":1431.36,"endTime":1435.2,"body":"lots and lots of luminosity"},{"startTime":1435.2,"endTime":1437.84,"body":"even though you're at"},{"startTime":1435.2,"endTime":1437.84,"body":"a very low temperature,"},{"startTime":1437.84,"endTime":1439.28,"body":"and those stars,"},{"startTime":1439.28,"endTime":1441.65,"body":"at least some of the ones on the left,"},{"startTime":1441.65,"endTime":1443.78,"body":"will correspond to the red giants"},{"startTime":1443.78,"endTime":1446.603,"body":"that I spoke of in my previous lecture."},{"startTime":1448.25,"endTime":1450.17,"body":"Some of these other giant stars,"},{"startTime":1450.17,"endTime":1452.9,"body":"right at the top, but"},{"startTime":1450.17,"endTime":1452.9,"body":"off the main sequence,"},{"startTime":1452.9,"endTime":1454.71,"body":"are ones that have expanded"},{"startTime":1455.66,"endTime":1460.103,"body":"because of changes within"},{"startTime":1455.66,"endTime":1460.103,"body":"the center of the star."},{"startTime":1461.54,"endTime":1466.46,"body":"So where a star falls"},{"startTime":1461.54,"endTime":1466.46,"body":"on one of these diagrams"},{"startTime":1466.46,"endTime":1471.35,"body":"tells us a lot about its"},{"startTime":1466.46,"endTime":1471.35,"body":"temperature, its mass,"},{"startTime":1471.35,"endTime":1473.183,"body":"and how old it must be."},{"startTime":1474.47,"endTime":1477.11,"body":"If you form one of these diagrams"},{"startTime":1477.11,"endTime":1480.05,"body":"for just a single cluster in the sky,"},{"startTime":1480.05,"endTime":1482.36,"body":"for example Omega Centaurus,"},{"startTime":1482.36,"endTime":1484.31,"body":"as has happened here,"},{"startTime":1484.31,"endTime":1487.16,"body":"then all the stars you're looking at"},{"startTime":1487.16,"endTime":1490.76,"body":"probably have very similar"},{"startTime":1487.16,"endTime":1490.76,"body":"chemical composition"},{"startTime":1490.76,"endTime":1494.513,"body":"because they formed from the"},{"startTime":1490.76,"endTime":1494.513,"body":"same original cloud of gas,"},{"startTime":1495.38,"endTime":1498.62,"body":"they collapsed at around the same time,"},{"startTime":1498.62,"endTime":1502.19,"body":"so they're pretty much of the same age."},{"startTime":1502.19,"endTime":1503.78,"body":"So to an extent,"},{"startTime":1503.78,"endTime":1505.85,"body":"one of these diagrams"},{"startTime":1505.85,"endTime":1508.67,"body":"is as important for stellar astrophysics"},{"startTime":1508.67,"endTime":1511.733,"body":"as the Periodic Table is for chemistry."},{"startTime":1512.81,"endTime":1516.11,"body":"Now, this diagram is"},{"startTime":1512.81,"endTime":1516.11,"body":"known as the HR diagram."},{"startTime":1516.11,"endTime":1519.38,"body":"Now, don't think about"},{"startTime":1516.11,"endTime":1519.38,"body":"HR as in human resources,"},{"startTime":1519.38,"endTime":1521.39,"body":"I'm sure they have diagrams too,"},{"startTime":1521.39,"endTime":1526.13,"body":"but this particular diagram"},{"startTime":1521.39,"endTime":1526.13,"body":"is known as the HR diagram"},{"startTime":1526.13,"endTime":1528.143,"body":"after Hertzsprung and Russell."},{"startTime":1529.25,"endTime":1533.45,"body":"Hertzsprung was Danish"},{"startTime":1529.25,"endTime":1533.45,"body":"and Russell was American,"},{"startTime":1533.45,"endTime":1538.45,"body":"and they independently established"},{"startTime":1533.45,"endTime":1538.45,"body":"this behavior of stars,"},{"startTime":1538.94,"endTime":1542.42,"body":"the fact that you have this"},{"startTime":1538.94,"endTime":1542.42,"body":"main sequence of stars here"},{"startTime":1542.42,"endTime":1543.47,"body":"and then giants,"},{"startTime":1543.47,"endTime":1545.69,"body":"which are doing rather funky things"},{"startTime":1545.69,"endTime":1549.203,"body":"after the normal fusion"},{"startTime":1545.69,"endTime":1549.203,"body":"processes have ended."},{"startTime":1550.04,"endTime":1552.56,"body":"So where you are on this luminosity track"},{"startTime":1552.56,"endTime":1554.663,"body":"depends strongly on mass."},{"startTime":1556.25,"endTime":1559.76,"body":"When your Tarantula Nebula"},{"startTime":1559.76,"endTime":1564.14,"body":"ultimately collapses into"},{"startTime":1559.76,"endTime":1564.14,"body":"your cluster of stars,"},{"startTime":1564.14,"endTime":1565.94,"body":"like Omega Cen,"},{"startTime":1565.94,"endTime":1567.44,"body":"the more massive stars"},{"startTime":1567.44,"endTime":1571.49,"body":"will be on the top-left"},{"startTime":1567.44,"endTime":1571.49,"body":"of this main sequence,"},{"startTime":1571.49,"endTime":1574.34,"body":"and the lower mass stars"},{"startTime":1571.49,"endTime":1574.34,"body":"will be further down,"},{"startTime":1574.34,"endTime":1577.073,"body":"less luminous and lower temperatures."},{"startTime":1577.94,"endTime":1580.88,"body":"Now, stars do come in"},{"startTime":1577.94,"endTime":1580.88,"body":"all shapes and forms,"},{"startTime":1580.88,"endTime":1583.28,"body":"and I just want to illustrate this"},{"startTime":1583.28,"endTime":1586.88,"body":"with the help of some"},{"startTime":1583.28,"endTime":1586.88,"body":"figures by David Jarvis."},{"startTime":1586.88,"endTime":1589.4,"body":"Just to help calibrate sizes now,"},{"startTime":1589.4,"endTime":1591.83,"body":"we're thinking about"},{"startTime":1589.4,"endTime":1591.83,"body":"the diameters of stars,"},{"startTime":1591.83,"endTime":1594.32,"body":"over there on the left we've got Jupiter,"},{"startTime":1594.32,"endTime":1595.94,"body":"Jupiter is lovely,"},{"startTime":1595.94,"endTime":1599.03,"body":"the stripy planet in our solar system"},{"startTime":1599.03,"endTime":1601.46,"body":"that we all love because it rotates,"},{"startTime":1601.46,"endTime":1604.07,"body":"and because it's pretty,"},{"startTime":1601.46,"endTime":1604.07,"body":"and it's got stripes."},{"startTime":1604.07,"endTime":1606.41,"body":"If Jupiter had a bit more mass,"},{"startTime":1606.41,"endTime":1608.78,"body":"it would be a star in its own right,"},{"startTime":1608.78,"endTime":1612.95,"body":"but it hasn't got quite enough"},{"startTime":1608.78,"endTime":1612.95,"body":"mass to collapse quite enough"},{"startTime":1612.95,"endTime":1614.81,"body":"for the densities to be high enough,"},{"startTime":1614.81,"endTime":1616.52,"body":"for the temperatures to be high enough"},{"startTime":1616.52,"endTime":1618.86,"body":"for fusion to take place"},{"startTime":1618.86,"endTime":1620.75,"body":"so it's a planet, it's not a star,"},{"startTime":1620.75,"endTime":1624.47,"body":"but we've got a feeling"},{"startTime":1620.75,"endTime":1624.47,"body":"for how big Jupiter is."},{"startTime":1624.47,"endTime":1627.773,"body":"Next along is a star called Wolf 359."},{"startTime":1628.73,"endTime":1632.87,"body":"Wolf 359 is just about a star,"},{"startTime":1632.87,"endTime":1635.3,"body":"it's one up on Jupiter,"},{"startTime":1635.3,"endTime":1638.0,"body":"but it's a red dwarf and it's very faint,"},{"startTime":1638.0,"endTime":1639.77,"body":"and we can only see it"},{"startTime":1639.77,"endTime":1642.86,"body":"because of its proximity to the Sun,"},{"startTime":1642.86,"endTime":1643.693,"body":"it's something like"},{"startTime":1643.693,"endTime":1647.06,"body":"the fifth nearest star away from the Sun,"},{"startTime":1647.06,"endTime":1649.79,"body":"Proxima Centauri being the closest,"},{"startTime":1649.79,"endTime":1652.79,"body":"it's only about nine"},{"startTime":1649.79,"endTime":1652.79,"body":"light years from Earth,"},{"startTime":1652.79,"endTime":1656.48,"body":"whereas Proxima Centauri is"},{"startTime":1652.79,"endTime":1656.48,"body":"four light years from Earth,"},{"startTime":1656.48,"endTime":1658.82,"body":"you can see it in an amateur telescope"},{"startTime":1658.82,"endTime":1660.17,"body":"if you point in the right direction"},{"startTime":1660.17,"endTime":1662.63,"body":"and there aren't clouds in the way."},{"startTime":1662.63,"endTime":1664.1,"body":"Next up, we've got the Sun,"},{"startTime":1664.1,"endTime":1666.5,"body":"next up, we've got Sirius."},{"startTime":1666.5,"endTime":1669.08,"body":"So keep Sirius relative to the Sun"},{"startTime":1669.08,"endTime":1670.283,"body":"in your mind's eye,"},{"startTime":1671.3,"endTime":1673.1,"body":"and now let's rescale."},{"startTime":1673.1,"endTime":1677.99,"body":"Here's Sirius, now Pollux,"},{"startTime":1673.1,"endTime":1677.99,"body":"now Arcturus, now Aldebaran,"},{"startTime":1677.99,"endTime":1680.933,"body":"which you can see in the winter skies."},{"startTime":1681.77,"endTime":1685.103,"body":"Now keep Aldebaran in your"},{"startTime":1681.77,"endTime":1685.103,"body":"mind's eye, let's rescale."},{"startTime":1686.48,"endTime":1687.313,"body":"There's Rigel,"},{"startTime":1687.313,"endTime":1688.146,"body":"remember Rigel,"},{"startTime":1688.146,"endTime":1692.57,"body":"kind of on the bottom-right"},{"startTime":1688.146,"endTime":1692.57,"body":"of the Orion constellation?"},{"startTime":1693.95,"endTime":1695.99,"body":"Now Antares, now Betelgeuse,"},{"startTime":1695.99,"endTime":1698.69,"body":"the orange thing on the top-left of Orion."},{"startTime":1698.69,"endTime":1701.81,"body":"Now let's rescale, and so on."},{"startTime":1701.81,"endTime":1704.15,"body":"Probably the most massive"},{"startTime":1701.81,"endTime":1704.15,"body":"star we know about"},{"startTime":1704.15,"endTime":1706.58,"body":"is VY Canis Majoris,"},{"startTime":1706.58,"endTime":1707.78,"body":"and this is pretty massive."},{"startTime":1707.78,"endTime":1709.76,"body":"It's not the most massive star we know,"},{"startTime":1709.76,"endTime":1712.58,"body":"but it's one of the largest in diameter,"},{"startTime":1712.58,"endTime":1717.23,"body":"its mass is about 17"},{"startTime":1712.58,"endTime":1717.23,"body":"times the mass of our sun."},{"startTime":1717.23,"endTime":1722.23,"body":"And so the sizes of the"},{"startTime":1717.23,"endTime":1722.23,"body":"stars that we can observe"},{"startTime":1723.23,"endTime":1726.35,"body":"depend partly on the mass of a star,"},{"startTime":1726.35,"endTime":1728.72,"body":"because the mass will tend to pull in"},{"startTime":1728.72,"endTime":1730.88,"body":"and tend to cause more collapse,"},{"startTime":1730.88,"endTime":1733.858,"body":"but equally, a star will then puff out"},{"startTime":1733.858,"endTime":1738.38,"body":"if it's reached that"},{"startTime":1733.858,"endTime":1738.38,"body":"stage in its evolution."},{"startTime":1738.38,"endTime":1740.63,"body":"Why will a star puff out?"},{"startTime":1740.63,"endTime":1745.63,"body":"It's important to realize that"},{"startTime":1740.63,"endTime":1745.63,"body":"the entire lifetime of a star"},{"startTime":1746.87,"endTime":1748.43,"body":"is one long struggle,"},{"startTime":1748.43,"endTime":1751.58,"body":"or rather one long series of struggles."},{"startTime":1751.58,"endTime":1752.96,"body":"There are two competing effects,"},{"startTime":1752.96,"endTime":1756.32,"body":"one is gravity, as I've indicated."},{"startTime":1756.32,"endTime":1761.32,"body":"Now, if if collapsing"},{"startTime":1756.32,"endTime":1761.32,"body":"matter were completely cold"},{"startTime":1761.48,"endTime":1765.38,"body":"and there was no"},{"startTime":1761.48,"endTime":1765.38,"body":"viscosity, and no anything"},{"startTime":1765.38,"endTime":1766.643,"body":"other than gravity,"},{"startTime":1767.75,"endTime":1770.3,"body":"it would collapse to a"},{"startTime":1767.75,"endTime":1770.3,"body":"very dense point indeed,"},{"startTime":1770.3,"endTime":1775.3,"body":"but the thermal energy increases,"},{"startTime":1770.3,"endTime":1775.3,"body":"and the density increases,"},{"startTime":1775.46,"endTime":1776.63,"body":"and so you get temperatures"},{"startTime":1776.63,"endTime":1779.513,"body":"which are high enough to"},{"startTime":1776.63,"endTime":1779.513,"body":"cause fusion, as I've said."},{"startTime":1783.74,"endTime":1786.41,"body":"And so offsetting that"},{"startTime":1783.74,"endTime":1786.41,"body":"gravitational collapse"},{"startTime":1786.41,"endTime":1788.45,"body":"is this thermal energy,"},{"startTime":1788.45,"endTime":1790.16,"body":"and that takes two forms."},{"startTime":1790.16,"endTime":1793.76,"body":"One is the internal energy"},{"startTime":1790.16,"endTime":1793.76,"body":"of the atoms and the ions"},{"startTime":1793.76,"endTime":1796.85,"body":"that are whizzing around"},{"startTime":1793.76,"endTime":1796.85,"body":"in the core of a star,"},{"startTime":1796.85,"endTime":1799.16,"body":"and the other is the radiation pressure,"},{"startTime":1799.16,"endTime":1803.75,"body":"the momentum due to"},{"startTime":1799.16,"endTime":1803.75,"body":"the photons themselves."},{"startTime":1803.75,"endTime":1807.29,"body":"If you've lost a lot of the fusion"},{"startTime":1807.29,"endTime":1811.46,"body":"that's going on in the"},{"startTime":1807.29,"endTime":1811.46,"body":"central core of a star,"},{"startTime":1811.46,"endTime":1814.85,"body":"then you lose that sort"},{"startTime":1811.46,"endTime":1814.85,"body":"of internal heat engine,"},{"startTime":1814.85,"endTime":1816.8,"body":"and so you risk collapse."},{"startTime":1816.8,"endTime":1818.63,"body":"But if you have collapse,"},{"startTime":1818.63,"endTime":1820.85,"body":"then you can reach higher densities again,"},{"startTime":1820.85,"endTime":1822.8,"body":"and higher temperatures,"},{"startTime":1822.8,"endTime":1825.44,"body":"and even if you've used"},{"startTime":1822.8,"endTime":1825.44,"body":"up all your hydrogen,"},{"startTime":1825.44,"endTime":1829.34,"body":"things like helium can"},{"startTime":1825.44,"endTime":1829.34,"body":"start undergoing fusion,"},{"startTime":1829.34,"endTime":1832.28,"body":"more of that in just a moment,"},{"startTime":1832.28,"endTime":1833.6,"body":"but hang on to the fact for now"},{"startTime":1833.6,"endTime":1835.4,"body":"that this main sequence"},{"startTime":1835.4,"endTime":1840.143,"body":"is where normal stars are"},{"startTime":1835.4,"endTime":1840.143,"body":"normally fusing hydrogen."},{"startTime":1841.37,"endTime":1843.26,"body":"When they've used up all their hydrogen,"},{"startTime":1843.26,"endTime":1847.23,"body":"they'll typically drift off"},{"startTime":1843.26,"endTime":1847.23,"body":"the main sequence to the right"},{"startTime":1848.33,"endTime":1851.45,"body":"and expand, they'll get bigger,"},{"startTime":1851.45,"endTime":1854.87,"body":"and even if the temperature"},{"startTime":1851.45,"endTime":1854.87,"body":"isn't that great,"},{"startTime":1854.87,"endTime":1858.29,"body":"because helium will now be the atom"},{"startTime":1858.29,"endTime":1860.15,"body":"that's predominantly fusing together"},{"startTime":1860.15,"endTime":1862.16,"body":"to form carbon, and other things,"},{"startTime":1862.16,"endTime":1865.67,"body":"you will still get quite"},{"startTime":1862.16,"endTime":1865.67,"body":"a lot of luminosity."},{"startTime":1865.67,"endTime":1867.17,"body":"So there'll be a bit of a cycle"},{"startTime":1867.17,"endTime":1870.05,"body":"where you use up all the hydrogen"},{"startTime":1870.05,"endTime":1872.96,"body":"and that heat source goes,"},{"startTime":1872.96,"endTime":1875.06,"body":"yikes, there's a collapse,"},{"startTime":1875.06,"endTime":1877.55,"body":"then the density increases again"},{"startTime":1877.55,"endTime":1878.9,"body":"and the temperature hikes up,"},{"startTime":1878.9,"endTime":1882.65,"body":"and then helium can then undergo fusion."},{"startTime":1882.65,"endTime":1885.47,"body":"Now, that's really the end of"},{"startTime":1882.65,"endTime":1885.47,"body":"the game for low-mass stars"},{"startTime":1885.47,"endTime":1888.05,"body":"that I talked about in"},{"startTime":1885.47,"endTime":1888.05,"body":"my previous lecture,"},{"startTime":1888.05,"endTime":1892.04,"body":"the stars that go off and form red giants,"},{"startTime":1892.04,"endTime":1894.74,"body":"but when you have more massive stars,"},{"startTime":1894.74,"endTime":1896.603,"body":"the story isn't over."},{"startTime":1898.4,"endTime":1901.04,"body":"I think I've already made this"},{"startTime":1898.4,"endTime":1901.04,"body":"point that the HR diagram,"},{"startTime":1901.04,"endTime":1902.75,"body":"the Hertzsprung-Russell diagram,"},{"startTime":1902.75,"endTime":1904.73,"body":"for a single cluster of stars"},{"startTime":1904.73,"endTime":1906.59,"body":"can be very instructive"},{"startTime":1906.59,"endTime":1909.47,"body":"about the distribution"},{"startTime":1906.59,"endTime":1909.47,"body":"of masses that you get"},{"startTime":1909.47,"endTime":1911.99,"body":"because they're all the same age,"},{"startTime":1911.99,"endTime":1914.81,"body":"so they'll have the same t-zero,"},{"startTime":1914.81,"endTime":1919.81,"body":"they all started off the"},{"startTime":1914.81,"endTime":1919.81,"body":"starting blocks at the same time."},{"startTime":1920.45,"endTime":1922.52,"body":"So what about this cyclic process,"},{"startTime":1922.52,"endTime":1926.3,"body":"this fight, this competition"},{"startTime":1926.3,"endTime":1928.19,"body":"between gravity pulling things inwards"},{"startTime":1928.19,"endTime":1932.333,"body":"and the thermal energy trying"},{"startTime":1928.19,"endTime":1932.333,"body":"to offset that collapse?"},{"startTime":1933.26,"endTime":1934.52,"body":"As I've already indicated,"},{"startTime":1934.52,"endTime":1936.053,"body":"in low-mass stars,"},{"startTime":1936.95,"endTime":1939.95,"body":"once helium fusion has occurred,"},{"startTime":1939.95,"endTime":1943.91,"body":"the mass isn't enough for"},{"startTime":1939.95,"endTime":1943.91,"body":"the star to collapse enough"},{"startTime":1943.91,"endTime":1945.86,"body":"for the gravity to be enough"},{"startTime":1945.86,"endTime":1948.47,"body":"to cause the temperatures"},{"startTime":1945.86,"endTime":1948.47,"body":"to be high enough"},{"startTime":1948.47,"endTime":1950.9,"body":"for anything else to fuse."},{"startTime":1950.9,"endTime":1953.33,"body":"As you go through heavier"},{"startTime":1950.9,"endTime":1953.33,"body":"and heavier elements"},{"startTime":1953.33,"endTime":1954.98,"body":"in the Periodic Table,"},{"startTime":1954.98,"endTime":1958.973,"body":"it is harder and harder to"},{"startTime":1954.98,"endTime":1958.973,"body":"get them to fuse together."},{"startTime":1959.99,"endTime":1962.21,"body":"In nuclear physics,"},{"startTime":1962.21,"endTime":1965.84,"body":"if someone says it is"},{"startTime":1962.21,"endTime":1965.84,"body":"harder for this to happen,"},{"startTime":1965.84,"endTime":1969.89,"body":"that can usually be overcome"},{"startTime":1965.84,"endTime":1969.89,"body":"by winding up the temperature,"},{"startTime":1969.89,"endTime":1971.42,"body":"but in low-mass stars,"},{"startTime":1971.42,"endTime":1973.31,"body":"there's no mechanism for doing that,"},{"startTime":1973.31,"endTime":1975.41,"body":"you can't attain the densities,"},{"startTime":1975.41,"endTime":1978.98,"body":"so, this is a slide from"},{"startTime":1975.41,"endTime":1978.98,"body":"my previous lecture,"},{"startTime":1978.98,"endTime":1980.39,"body":"hydrogen burning"},{"startTime":1980.39,"endTime":1984.26,"body":"is replaced by helium"},{"startTime":1980.39,"endTime":1984.26,"body":"burning and helium fusion,"},{"startTime":1984.26,"endTime":1985.61,"body":"which, within the core,"},{"startTime":1985.61,"endTime":1987.47,"body":"puffs up that outer shell,"},{"startTime":1987.47,"endTime":1991.4,"body":"giving it a big diameter,"},{"startTime":1987.47,"endTime":1991.4,"body":"a giant sized diameter,"},{"startTime":1991.4,"endTime":1995.093,"body":"lots of luminosity, but"},{"startTime":1991.4,"endTime":1995.093,"body":"very low temperatures."},{"startTime":1996.11,"endTime":1998.063,"body":"When all the hydrogen is used up,"},{"startTime":2001.3,"endTime":2004.75,"body":"it's game over for a low-mass star,"},{"startTime":2004.75,"endTime":2007.21,"body":"the central core will"},{"startTime":2004.75,"endTime":2007.21,"body":"collapse and collapse"},{"startTime":2007.21,"endTime":2008.35,"body":"and form a white dwarf,"},{"startTime":2008.35,"endTime":2012.343,"body":"in the way that I discussed"},{"startTime":2008.35,"endTime":2012.343,"body":"in my lecture last time."},{"startTime":2013.24,"endTime":2015.13,"body":"But for high-mass stars,"},{"startTime":2015.13,"endTime":2017.23,"body":"the game is very much not over"},{"startTime":2017.23,"endTime":2020.23,"body":"when the helium has finished fusing,"},{"startTime":2020.23,"endTime":2022.81,"body":"when the hydrogen has, first"},{"startTime":2020.23,"endTime":2022.81,"body":"of all, finished fusing,"},{"startTime":2022.81,"endTime":2025.84,"body":"and then the helium has finished fusing."},{"startTime":2025.84,"endTime":2026.71,"body":"On the contrary,"},{"startTime":2026.71,"endTime":2029.14,"body":"the pressures and the temperatures"},{"startTime":2029.14,"endTime":2031.18,"body":"in that core that keeps"},{"startTime":2029.14,"endTime":2031.18,"body":"wanting to collapse,"},{"startTime":2031.18,"endTime":2032.563,"body":"and wanting to collapse,"},{"startTime":2033.4,"endTime":2036.07,"body":"but is regulated by the fact"},{"startTime":2036.07,"endTime":2038.71,"body":"that when the temperatures increase"},{"startTime":2038.71,"endTime":2040.45,"body":"because the star has collapsed,"},{"startTime":2040.45,"endTime":2044.2,"body":"you start off a whole"},{"startTime":2040.45,"endTime":2044.2,"body":"new fusion cycle again."},{"startTime":2044.2,"endTime":2047.77,"body":"For example, carbon fusion can begin"},{"startTime":2047.77,"endTime":2050.47,"body":"if the star is sufficiently massive,"},{"startTime":2050.47,"endTime":2054.28,"body":"and then the fusion of"},{"startTime":2050.47,"endTime":2054.28,"body":"oxygen atoms can take place."},{"startTime":2054.28,"endTime":2056.17,"body":"These get harder and harder"},{"startTime":2056.17,"endTime":2058.84,"body":"and require higher and"},{"startTime":2056.17,"endTime":2058.84,"body":"higher temperatures,"},{"startTime":2058.84,"endTime":2061.9,"body":"but you can do it if"},{"startTime":2058.84,"endTime":2061.9,"body":"you've got enough mass"},{"startTime":2061.9,"endTime":2064.45,"body":"and you've used up all"},{"startTime":2061.9,"endTime":2064.45,"body":"the preceding elements,"},{"startTime":2064.45,"endTime":2068.02,"body":"so the collapse is really"},{"startTime":2064.45,"endTime":2068.02,"body":"very, very intense."},{"startTime":2068.02,"endTime":2071.05,"body":"You can then start fusing"},{"startTime":2068.02,"endTime":2071.05,"body":"together heavier elements still,"},{"startTime":2071.05,"endTime":2073.873,"body":"such as neon, and magnesium, and silicon,"},{"startTime":2074.89,"endTime":2079.89,"body":"and these will continue to"},{"startTime":2074.89,"endTime":2079.89,"body":"power the star as a giant."},{"startTime":2082.12,"endTime":2085.54,"body":"In the process of all these"},{"startTime":2082.12,"endTime":2085.54,"body":"different fusion cycles,"},{"startTime":2085.54,"endTime":2087.94,"body":"first with hydrogen, then with helium,"},{"startTime":2087.94,"endTime":2091.45,"body":"but then, uniquely for the"},{"startTime":2087.94,"endTime":2091.45,"body":"case of high-mass stars,"},{"startTime":2091.45,"endTime":2096.45,"body":"carbon, oxygen, neon, magnesium,"},{"startTime":2091.45,"endTime":2096.45,"body":"silicon, sulfur as well,"},{"startTime":2097.12,"endTime":2099.19,"body":"a process is taking place"},{"startTime":2099.19,"endTime":2103.06,"body":"which we know in astrophysics"},{"startTime":2099.19,"endTime":2103.06,"body":"as nucleosynthesis,"},{"startTime":2103.06,"endTime":2106.81,"body":"the cookery, the synthesis of nuclei,"},{"startTime":2106.81,"endTime":2110.413,"body":"the bits in the middle of the atoms."},{"startTime":2111.46,"endTime":2113.53,"body":"Now, there are four principle ways"},{"startTime":2113.53,"endTime":2117.52,"body":"in which nucleosynthesis"},{"startTime":2113.53,"endTime":2117.52,"body":"takes place in the Universe."},{"startTime":2117.52,"endTime":2118.78,"body":"The first nucleosynthesis"},{"startTime":2118.78,"endTime":2121.84,"body":"was shortly after the beginning of time,"},{"startTime":2121.84,"endTime":2125.53,"body":"in the first few minutes"},{"startTime":2121.84,"endTime":2125.53,"body":"after the Big Bang itself,"},{"startTime":2125.53,"endTime":2130.27,"body":"and I've described that in my"},{"startTime":2125.53,"endTime":2130.27,"body":"second ever Gresham lecture,"},{"startTime":2130.27,"endTime":2132.52,"body":"entitled \"Frozen In Time,\""},{"startTime":2132.52,"endTime":2134.47,"body":"so I'm not going to address that today."},{"startTime":2135.94,"endTime":2138.79,"body":"I've discussed the fact"},{"startTime":2135.94,"endTime":2138.79,"body":"in in my previous lecture,"},{"startTime":2138.79,"endTime":2141.55,"body":"on the end of low-mass stars like our sun,"},{"startTime":2141.55,"endTime":2144.55,"body":"that nucleosynthesis of helium and carbon"},{"startTime":2144.55,"endTime":2146.95,"body":"takes place in those stars,"},{"startTime":2146.95,"endTime":2147.783,"body":"and that's great,"},{"startTime":2147.783,"endTime":2149.803,"body":"the world needs carbon, kind of."},{"startTime":2150.76,"endTime":2152.533,"body":"Notice I didn't say CO2."},{"startTime":2154.06,"endTime":2155.89,"body":"For high-mass stars,"},{"startTime":2155.89,"endTime":2159.79,"body":"the nucleosynthesis of"},{"startTime":2155.89,"endTime":2159.79,"body":"heavier elements still,"},{"startTime":2159.79,"endTime":2161.56,"body":"neon, magnesium, silicon"},{"startTime":2161.56,"endTime":2163.183,"body":"also takes place,"},{"startTime":2164.02,"endTime":2168.34,"body":"but life couldn't exist"},{"startTime":2164.02,"endTime":2168.34,"body":"with just those elements,"},{"startTime":2168.34,"endTime":2173.34,"body":"and in fact, what we need"},{"startTime":2168.34,"endTime":2173.34,"body":"is heavier elements still"},{"startTime":2173.8,"endTime":2176.38,"body":"if life is going to exist."},{"startTime":2176.38,"endTime":2179.44,"body":"So these are the various"},{"startTime":2176.38,"endTime":2179.44,"body":"different fusion processes"},{"startTime":2179.44,"endTime":2183.493,"body":"that happen in different"},{"startTime":2179.44,"endTime":2183.493,"body":"layers inside a massive star,"},{"startTime":2184.39,"endTime":2186.7,"body":"the heaviest elements doing fusion"},{"startTime":2186.7,"endTime":2189.22,"body":"closest in to the center of the star,"},{"startTime":2189.22,"endTime":2191.23,"body":"where the temperatures are high enough"},{"startTime":2191.23,"endTime":2194.56,"body":"for those nuclear reactions to take place,"},{"startTime":2194.56,"endTime":2195.393,"body":"and you can see"},{"startTime":2195.393,"endTime":2199.24,"body":"that I've just illustrated what"},{"startTime":2195.393,"endTime":2199.24,"body":"those nuclear reactions are."},{"startTime":2199.24,"endTime":2201.49,"body":"But these nuclear reactions"},{"startTime":2201.49,"endTime":2206.05,"body":"inside the fusion"},{"startTime":2201.49,"endTime":2206.05,"body":"processes of massive stars"},{"startTime":2206.05,"endTime":2210.79,"body":"are insufficient to populate"},{"startTime":2206.05,"endTime":2210.79,"body":"all of the Periodic Table,"},{"startTime":2210.79,"endTime":2212.293,"body":"so where do they come from?"},{"startTime":2213.52,"endTime":2216.97,"body":"They come in the few seconds"},{"startTime":2216.97,"endTime":2221.35,"body":"of the ignition of a supernova explosion."},{"startTime":2221.35,"endTime":2222.92,"body":"So you can get a lot of iron"},{"startTime":2225.64,"endTime":2228.97,"body":"just in the the very"},{"startTime":2225.64,"endTime":2228.97,"body":"end-times of a high-mass star"},{"startTime":2228.97,"endTime":2230.593,"body":"before it goes supernova,"},{"startTime":2231.91,"endTime":2236.8,"body":"and in the the initial aftermath"},{"startTime":2231.91,"endTime":2236.8,"body":"of a supernova explosion,"},{"startTime":2236.8,"endTime":2239.53,"body":"and you can get heavier elements still."},{"startTime":2239.53,"endTime":2241.42,"body":"I put it to you"},{"startTime":2241.42,"endTime":2244.3,"body":"that anyone who has got red blood cells"},{"startTime":2244.3,"endTime":2246.61,"body":"coursing through their"},{"startTime":2244.3,"endTime":2246.61,"body":"veins and their brain,"},{"startTime":2246.61,"endTime":2249.49,"body":"and I trust that's all of us,"},{"startTime":2249.49,"endTime":2253.333,"body":"would not exist if massive"},{"startTime":2249.49,"endTime":2253.333,"body":"stars had not gone bang,"},{"startTime":2254.32,"endTime":2257.32,"body":"those of us wearing gold"},{"startTime":2254.32,"endTime":2257.32,"body":"jewelry would not be wearing it"},{"startTime":2257.32,"endTime":2261.1,"body":"if it had not been for"},{"startTime":2257.32,"endTime":2261.1,"body":"supernova explosions,"},{"startTime":2261.1,"endTime":2264.04,"body":"so hooray for supernovae."},{"startTime":2264.04,"endTime":2265.6,"body":"They may be rare,"},{"startTime":2265.6,"endTime":2269.89,"body":"but they are crucial for life to exist."},{"startTime":2269.89,"endTime":2271.84,"body":"So it's important to appreciate"},{"startTime":2271.84,"endTime":2276.37,"body":"that a supernova explosion"},{"startTime":2271.84,"endTime":2276.37,"body":"happens not when a star is born,"},{"startTime":2276.37,"endTime":2278.35,"body":"but when a star dies,"},{"startTime":2278.35,"endTime":2281.083,"body":"that its fusion times are over,"},{"startTime":2282.46,"endTime":2283.293,"body":"the collapse that,"},{"startTime":2283.293,"endTime":2286.15,"body":"when all the different"},{"startTime":2283.293,"endTime":2286.15,"body":"elements that can fuse normally"},{"startTime":2286.15,"endTime":2287.47,"body":"have collapsed,"},{"startTime":2287.47,"endTime":2290.89,"body":"then there are various"},{"startTime":2287.47,"endTime":2290.89,"body":"collisions and disintegrations,"},{"startTime":2290.89,"endTime":2292.75,"body":"and bit more energy is given off,"},{"startTime":2292.75,"endTime":2297.28,"body":"and then the central core"},{"startTime":2292.75,"endTime":2297.28,"body":"can collapse completely"},{"startTime":2297.28,"endTime":2299.38,"body":"to a compact object."},{"startTime":2299.38,"endTime":2302.41,"body":"Much like as in the low-mass stars,"},{"startTime":2302.41,"endTime":2304.27,"body":"the central core of a low-mass star"},{"startTime":2304.27,"endTime":2307.45,"body":"will ultimately collapse"},{"startTime":2304.27,"endTime":2307.45,"body":"into a white dwarf,"},{"startTime":2307.45,"endTime":2309.85,"body":"the central core of a high-mass star"},{"startTime":2309.85,"endTime":2313.15,"body":"will still collapse into a compact object,"},{"startTime":2313.15,"endTime":2315.76,"body":"but a different kind of compact object,"},{"startTime":2315.76,"endTime":2317.77,"body":"either a neutron star,"},{"startTime":2317.77,"endTime":2321.37,"body":"for the lower mass examples"},{"startTime":2317.77,"endTime":2321.37,"body":"of the high-mass stars,"},{"startTime":2321.37,"endTime":2323.32,"body":"or a black hole"},{"startTime":2323.32,"endTime":2327.16,"body":"in the case of the higher"},{"startTime":2323.32,"endTime":2327.16,"body":"mass high-mass stars."},{"startTime":2327.16,"endTime":2328.87,"body":"And these supernovae,"},{"startTime":2328.87,"endTime":2332.44,"body":"regardless of whether the ultimate outcome"},{"startTime":2332.44,"endTime":2335.173,"body":"is a neutron star or a black hole,"},{"startTime":2336.01,"endTime":2338.86,"body":"these supernova explosions are responsible"},{"startTime":2338.86,"endTime":2343.86,"body":"for putting the heavy elements"},{"startTime":2338.86,"endTime":2343.86,"body":"into the interstellar medium,"},{"startTime":2343.9,"endTime":2346.39,"body":"spewing out lots of gas,"},{"startTime":2346.39,"endTime":2348.91,"body":"which then gets dense"},{"startTime":2346.39,"endTime":2348.91,"body":"enough, and dense enough"},{"startTime":2348.91,"endTime":2350.5,"body":"to form a nebula,"},{"startTime":2350.5,"endTime":2352.48,"body":"much like the Tarantula Nebula"},{"startTime":2352.48,"endTime":2354.61,"body":"I showed you at the start of my talk,"},{"startTime":2354.61,"endTime":2356.92,"body":"and then ultimately to collapse again"},{"startTime":2356.92,"endTime":2360.283,"body":"to form stars and planets like Earth."},{"startTime":2361.69,"endTime":2364.87,"body":"So excitingly, a supernova"},{"startTime":2361.69,"endTime":2364.87,"body":"does all those things"},{"startTime":2364.87,"endTime":2366.1,"body":"which matter for life,"},{"startTime":2366.1,"endTime":2367.66,"body":"but they can also give rise"},{"startTime":2367.66,"endTime":2370.213,"body":"to a neutron star or a black hole."},{"startTime":2371.2,"endTime":2372.61,"body":"Black holes and neutron stars"},{"startTime":2372.61,"endTime":2376.0,"body":"give rise to terribly"},{"startTime":2372.61,"endTime":2376.0,"body":"exciting astrophysics,"},{"startTime":2376.0,"endTime":2378.16,"body":"and I talked quite a bit about black holes"},{"startTime":2378.16,"endTime":2382.84,"body":"in my third lecture as Gresham professor,"},{"startTime":2382.84,"endTime":2385.147,"body":"which was entitled \"The End of Matter?\""},{"startTime":2387.4,"endTime":2389.11,"body":"How frequent are supernovae?"},{"startTime":2389.11,"endTime":2390.88,"body":"Well, on average,"},{"startTime":2390.88,"endTime":2393.493,"body":"they're thought to be"},{"startTime":2390.88,"endTime":2393.493,"body":"about one per century."},{"startTime":2394.6,"endTime":2396.94,"body":"Remember that handwritten fax"},{"startTime":2396.94,"endTime":2401.777,"body":"in the context of the supernova"},{"startTime":2396.94,"endTime":2401.777,"body":"that went off in 1987,"},{"startTime":2401.777,"endTime":2406.777,"body":"\"We've been waiting 350 years for this\"?"},{"startTime":2407.8,"endTime":2411.58,"body":"We haven't had a supernova for a long time"},{"startTime":2411.58,"endTime":2414.7,"body":"because it's only, on"},{"startTime":2411.58,"endTime":2414.7,"body":"average, one per century,"},{"startTime":2414.7,"endTime":2416.29,"body":"but they asked stochastic,"},{"startTime":2416.29,"endTime":2418.99,"body":"and we haven't had a really good supernova"},{"startTime":2418.99,"endTime":2422.293,"body":"for, well, centuries."},{"startTime":2423.7,"endTime":2427.66,"body":"The last really good one, in our galaxy,"},{"startTime":2427.66,"endTime":2430.57,"body":"that was close enough to"},{"startTime":2427.66,"endTime":2430.57,"body":"be observed and followed"},{"startTime":2430.57,"endTime":2431.833,"body":"was in 1604."},{"startTime":2433.66,"endTime":2436.15,"body":"It's known as Kepler's Supernova"},{"startTime":2436.15,"endTime":2440.05,"body":"because Johannes Kepler"},{"startTime":2436.15,"endTime":2440.05,"body":"studied it obsessively"},{"startTime":2440.05,"endTime":2443.413,"body":"and made some really"},{"startTime":2440.05,"endTime":2443.413,"body":"beautiful observations of it."},{"startTime":2445.36,"endTime":2448.03,"body":"This supernova was brighter than Jupiter"},{"startTime":2448.03,"endTime":2451.33,"body":"so it could easily be"},{"startTime":2448.03,"endTime":2451.33,"body":"seen in the naked eye,"},{"startTime":2451.33,"endTime":2452.59,"body":"and in fact, at its peak."},{"startTime":2452.59,"endTime":2456.193,"body":"it was brighter than any"},{"startTime":2452.59,"endTime":2456.193,"body":"other star in the night sky."},{"startTime":2457.27,"endTime":2461.233,"body":"It was visible for over"},{"startTime":2457.27,"endTime":2461.233,"body":"a year to the naked eye,"},{"startTime":2462.16,"endTime":2464.44,"body":"and it spewed out quite a lot of mass,"},{"startTime":2464.44,"endTime":2467.41,"body":"because when you get that"},{"startTime":2464.44,"endTime":2467.41,"body":"core collapse for supernovae,"},{"startTime":2467.41,"endTime":2471.7,"body":"quite a lot of mass is flung"},{"startTime":2467.41,"endTime":2471.7,"body":"out in a big shockwave,"},{"startTime":2471.7,"endTime":2473.98,"body":"a big, explosive shockwave,"},{"startTime":2473.98,"endTime":2476.44,"body":"that, in the presence of other gas clouds"},{"startTime":2476.44,"endTime":2478.3,"body":"can cause compression"},{"startTime":2478.3,"endTime":2481.12,"body":"and trigger the collapse"},{"startTime":2478.3,"endTime":2481.12,"body":"of other gas clouds"},{"startTime":2481.12,"endTime":2483.22,"body":"to form more new stars."},{"startTime":2483.22,"endTime":2488.22,"body":"Supernovae have a lot"},{"startTime":2483.22,"endTime":2488.22,"body":"of exciting influence"},{"startTime":2488.32,"endTime":2489.52,"body":"because they expand"},{"startTime":2489.52,"endTime":2493.123,"body":"at speeds of thousands"},{"startTime":2489.52,"endTime":2493.123,"body":"of kilometers per second."},{"startTime":2493.99,"endTime":2497.62,"body":"The kinetic energy of the gas"},{"startTime":2497.62,"endTime":2500.8,"body":"exploded out of Kepler's Supernova"},{"startTime":2500.8,"endTime":2505.8,"body":"was something like 10 to"},{"startTime":2500.8,"endTime":2505.8,"body":"the power of 44 Joules."},{"startTime":2506.5,"endTime":2510.85,"body":"For all the 4 1/2 billion"},{"startTime":2506.5,"endTime":2510.85,"body":"years that our sun has existed,"},{"startTime":2510.85,"endTime":2514.78,"body":"it still hasn't radiated that"},{"startTime":2510.85,"endTime":2514.78,"body":"much over its entire lifetime,"},{"startTime":2514.78,"endTime":2517.843,"body":"supernovae are seriously explosive."},{"startTime":2518.86,"endTime":2522.103,"body":"Just to help you calibrate"},{"startTime":2518.86,"endTime":2522.103,"body":"that amount of energy,"},{"startTime":2523.09,"endTime":2525.43,"body":"the energy use in the UK,"},{"startTime":2525.43,"endTime":2527.44,"body":"which is more than it should be,"},{"startTime":2527.44,"endTime":2528.94,"body":"in one year"},{"startTime":2528.94,"endTime":2532.57,"body":"is only 10 to the power of 19 Joules."},{"startTime":2532.57,"endTime":2535.84,"body":"Supernovae are seriously energetic events,"},{"startTime":2535.84,"endTime":2538.06,"body":"and here is an image"},{"startTime":2538.06,"endTime":2542.623,"body":"of what the remnant of"},{"startTime":2538.06,"endTime":2542.623,"body":"that supernova explosion"},{"startTime":2543.73,"endTime":2545.59,"body":"witnessed by Johannes Kepler"},{"startTime":2545.59,"endTime":2550.243,"body":"actually looks like if you"},{"startTime":2545.59,"endTime":2550.243,"body":"observe it today in X-rays."},{"startTime":2552.19,"endTime":2556.54,"body":"This supernova took"},{"startTime":2552.19,"endTime":2556.54,"body":"place in October of 1604,"},{"startTime":2556.54,"endTime":2560.11,"body":"it was prior to the Gunpowder"},{"startTime":2556.54,"endTime":2560.11,"body":"Plot by about a year,"},{"startTime":2560.11,"endTime":2564.52,"body":"the monarch at the time"},{"startTime":2560.11,"endTime":2564.52,"body":"was James VI of Scotland,"},{"startTime":2564.52,"endTime":2565.6,"body":"James I of England,"},{"startTime":2565.6,"endTime":2568.483,"body":"ultimately James VI of"},{"startTime":2565.6,"endTime":2568.483,"body":"everywhere, I think,"},{"startTime":2570.55,"endTime":2574.9,"body":"Gresham was still on its"},{"startTime":2570.55,"endTime":2574.9,"body":"first professor of astronomy,"},{"startTime":2574.9,"endTime":2577.0,"body":"I'm number 38,"},{"startTime":2577.0,"endTime":2580.723,"body":"we are overdue for a really"},{"startTime":2577.0,"endTime":2580.723,"body":"good galactic supernova."},{"startTime":2583.72,"endTime":2588.13,"body":"Here is the remnant of a"},{"startTime":2583.72,"endTime":2588.13,"body":"supernova that exploded in 1054."},{"startTime":2589.3,"endTime":2591.79,"body":"It was observed by Chinese astronomers,"},{"startTime":2591.79,"endTime":2596.79,"body":"it was observed by astronomers"},{"startTime":2591.79,"endTime":2596.79,"body":"in New Mexico, in the USA."},{"startTime":2596.83,"endTime":2601.33,"body":"All this debris is now"},{"startTime":2596.83,"endTime":2601.33,"body":"known as the Crab Nebula,"},{"startTime":2601.33,"endTime":2604.57,"body":"and the compact object at"},{"startTime":2601.33,"endTime":2604.57,"body":"the heart of this supernova"},{"startTime":2604.57,"endTime":2606.49,"body":"is a neutron star"},{"startTime":2606.49,"endTime":2608.59,"body":"that actually rotates"},{"startTime":2608.59,"endTime":2611.71,"body":"and spews out a whole"},{"startTime":2608.59,"endTime":2611.71,"body":"lot of charged particles"},{"startTime":2611.71,"endTime":2612.88,"body":"as it does so,"},{"startTime":2612.88,"endTime":2613.99,"body":"it's a pulsar,"},{"startTime":2613.99,"endTime":2615.673,"body":"it's a pretty exciting object."},{"startTime":2616.78,"endTime":2618.52,"body":"This guest star,"},{"startTime":2618.52,"endTime":2621.52,"body":"I'm reliably informed,"},{"startTime":2618.52,"endTime":2621.52,"body":"I don't speak Chinese,"},{"startTime":2621.52,"endTime":2625.06,"body":"is described in this account here,"},{"startTime":2625.06,"endTime":2626.953,"body":"where it's highlighted in yellow,"},{"startTime":2627.88,"endTime":2631.633,"body":"their nomenclature was to"},{"startTime":2627.88,"endTime":2631.633,"body":"describe it as a guest star."},{"startTime":2632.95,"endTime":2634.45,"body":"And there have been other stars,"},{"startTime":2634.45,"endTime":2639.45,"body":"the earliest supernova witnessed"},{"startTime":2634.45,"endTime":2639.45,"body":"and reported by the Chinese"},{"startTime":2640.0,"endTime":2643.15,"body":"was in 185 AD,"},{"startTime":2643.15,"endTime":2646.36,"body":"it's known as Supernova 185."},{"startTime":2646.36,"endTime":2650.773,"body":"The brightest one was in 1006 AD,"},{"startTime":2651.646,"endTime":2655.33,"body":"there were eyewitnesses in"},{"startTime":2651.646,"endTime":2655.33,"body":"China, Japan, Iraq, Egypt,"},{"startTime":2655.33,"endTime":2656.623,"body":"as well as Europe,"},{"startTime":2657.79,"endTime":2661.723,"body":"there was then another famous one in 1572,"},{"startTime":2662.56,"endTime":2664.48,"body":"which was studied by Tycho Brahe,"},{"startTime":2664.48,"endTime":2667.45,"body":"and then the one in 1604, Kepler's one,"},{"startTime":2667.45,"endTime":2669.343,"body":"the last serious one we had,"},{"startTime":2670.93,"endTime":2674.11,"body":"and it was profoundly"},{"startTime":2670.93,"endTime":2674.11,"body":"influential at the time"},{"startTime":2674.11,"endTime":2678.34,"body":"because the idea that"},{"startTime":2674.11,"endTime":2678.34,"body":"things exploded and changed"},{"startTime":2678.34,"endTime":2681.283,"body":"outside of the Solar"},{"startTime":2678.34,"endTime":2681.283,"body":"System, beyond the Moon,"},{"startTime":2682.33,"endTime":2686.68,"body":"significantly challenged"},{"startTime":2682.33,"endTime":2686.68,"body":"the Aristotelian idea"},{"startTime":2686.68,"endTime":2690.343,"body":"that the cosmos was static and unchanging."},{"startTime":2691.24,"endTime":2695.17,"body":"Boy, do we know that the"},{"startTime":2691.24,"endTime":2695.17,"body":"cosmos is anything but static"},{"startTime":2695.17,"endTime":2698.173,"body":"and anything but unchanging these days."},{"startTime":2699.52,"endTime":2703.93,"body":"So although we haven't had a"},{"startTime":2699.52,"endTime":2703.93,"body":"proper supernova in our galaxy"},{"startTime":2703.93,"endTime":2705.94,"body":"since 1604,"},{"startTime":2705.94,"endTime":2707.32,"body":"36 years ago,"},{"startTime":2707.32,"endTime":2711.04,"body":"there was a supernova in one"},{"startTime":2707.32,"endTime":2711.04,"body":"of our nearest neighbors,"},{"startTime":2711.04,"endTime":2713.65,"body":"in the Large Magellanic Cloud,"},{"startTime":2713.65,"endTime":2717.97,"body":"which is one of the Milky"},{"startTime":2713.65,"endTime":2717.97,"body":"Way's nextdoor neighbors,"},{"startTime":2717.97,"endTime":2721.12,"body":"it's the upper one of these two here."},{"startTime":2721.12,"endTime":2722.53,"body":"The Milky way,"},{"startTime":2722.53,"endTime":2727.21,"body":"much like its sibling,"},{"startTime":2722.53,"endTime":2727.21,"body":"almost, the Andromeda Galaxy,"},{"startTime":2727.21,"endTime":2730.75,"body":"has quite a few satellite galaxies,"},{"startTime":2730.75,"endTime":2733.03,"body":"little galaxies in their own right,"},{"startTime":2733.03,"endTime":2734.71,"body":"self-gravitating,"},{"startTime":2734.71,"endTime":2738.79,"body":"yet not unaware of the gravity"},{"startTime":2734.71,"endTime":2738.79,"body":"of the Andromeda Galaxy"},{"startTime":2738.79,"endTime":2741.85,"body":"or of the Milky Way Galaxy in addition."},{"startTime":2741.85,"endTime":2745.33,"body":"So it was in this galaxy here,"},{"startTime":2745.33,"endTime":2748.78,"body":"that's a neighbor of"},{"startTime":2745.33,"endTime":2748.78,"body":"our home, the Milky Way,"},{"startTime":2748.78,"endTime":2751.42,"body":"where the Tarantula Nebula is to be found,"},{"startTime":2751.42,"endTime":2756.07,"body":"and where this supernova"},{"startTime":2751.42,"endTime":2756.07,"body":"exploded, as I said, in 1987."},{"startTime":2757.66,"endTime":2759.34,"body":"Australia's largest telescope,"},{"startTime":2759.34,"endTime":2760.93,"body":"the Anglo-Australian Telescope,"},{"startTime":2760.93,"endTime":2765.22,"body":"made lots of observations of it in 1987,"},{"startTime":2765.22,"endTime":2767.71,"body":"most telescopes in the"},{"startTime":2765.22,"endTime":2767.71,"body":"world started pointing at it"},{"startTime":2767.71,"endTime":2770.29,"body":"if they were far south enough to see it,"},{"startTime":2770.29,"endTime":2771.52,"body":"and even to this day,"},{"startTime":2771.52,"endTime":2775.303,"body":"their finding chart is still"},{"startTime":2771.52,"endTime":2775.303,"body":"sellotaped to their fridge."},{"startTime":2776.17,"endTime":2778.24,"body":"Here's a more beautiful image"},{"startTime":2778.24,"endTime":2780.88,"body":"which the Anglo-Australian Telescope made"},{"startTime":2780.88,"endTime":2783.31,"body":"to commemorate 30 years"},{"startTime":2783.31,"endTime":2786.613,"body":"since that particular supernova went bang."},{"startTime":2787.51,"endTime":2790.21,"body":"Well, I love studying things that change,"},{"startTime":2790.21,"endTime":2793.15,"body":"and with my Global Jet"},{"startTime":2790.21,"endTime":2793.15,"body":"Watch network of telescopes,"},{"startTime":2793.15,"endTime":2794.29,"body":"I decided it would be fun"},{"startTime":2794.29,"endTime":2797.35,"body":"to see if I could get a"},{"startTime":2794.29,"endTime":2797.35,"body":"spectrum of that object"},{"startTime":2797.35,"endTime":2800.44,"body":"and split it up into its light"},{"startTime":2800.44,"endTime":2802.69,"body":"to see what elements were present."},{"startTime":2802.69,"endTime":2805.24,"body":"And sure enough, I could do that."},{"startTime":2805.24,"endTime":2809.23,"body":"Even with the relatively"},{"startTime":2805.24,"endTime":2809.23,"body":"small size of my telescopes,"},{"startTime":2809.23,"endTime":2812.14,"body":"you can see that I was"},{"startTime":2809.23,"endTime":2812.14,"body":"able to split up its light"},{"startTime":2812.14,"endTime":2815.443,"body":"into quite a lot of different elements."},{"startTime":2816.34,"endTime":2820.09,"body":"A spectrum is where you split starlight"},{"startTime":2820.09,"endTime":2822.32,"body":"into its constituent colors"},{"startTime":2823.589,"endTime":2827.83,"body":"with a grating, or a prism,"},{"startTime":2823.589,"endTime":2827.83,"body":"or something like that,"},{"startTime":2827.83,"endTime":2828.73,"body":"in much the same way"},{"startTime":2828.73,"endTime":2831.94,"body":"that raindrops in a"},{"startTime":2828.73,"endTime":2831.94,"body":"cloud disperse sunlight,"},{"startTime":2831.94,"endTime":2833.68,"body":"but we're looking at starlight,"},{"startTime":2833.68,"endTime":2835.78,"body":"or supernova light in this case."},{"startTime":2835.78,"endTime":2836.72,"body":"And you can see"},{"startTime":2837.7,"endTime":2841.0,"body":"that even with my"},{"startTime":2837.7,"endTime":2841.0,"body":"relatively small telescope,"},{"startTime":2841.0,"endTime":2844.09,"body":"even 3 1/2 decades after the explosion,"},{"startTime":2844.09,"endTime":2846.94,"body":"I can still detect iron, and nitrogen,"},{"startTime":2846.94,"endTime":2849.73,"body":"and a few other bits and pieces."},{"startTime":2849.73,"endTime":2851.56,"body":"So it's good fun to watch it"},{"startTime":2851.56,"endTime":2852.77,"body":"and to look for changes"},{"startTime":2852.77,"endTime":2857.683,"body":"in how that supernova"},{"startTime":2852.77,"endTime":2857.683,"body":"shell continues to expand,"},{"startTime":2858.79,"endTime":2860.83,"body":"but I'm one of a number of people"},{"startTime":2860.83,"endTime":2862.21,"body":"that is really looking forward"},{"startTime":2862.21,"endTime":2866.23,"body":"to the next galactic supernova,"},{"startTime":2866.23,"endTime":2869.59,"body":"the next supernova that is close to Earth"},{"startTime":2869.59,"endTime":2873.37,"body":"and that we can follow with"},{"startTime":2869.59,"endTime":2873.37,"body":"modern instrumentation."},{"startTime":2873.37,"endTime":2875.38,"body":"It is startling to realize"},{"startTime":2875.38,"endTime":2879.01,"body":"that we haven't had a"},{"startTime":2875.38,"endTime":2879.01,"body":"supernova in this galaxy"},{"startTime":2879.01,"endTime":2881.38,"body":"since the invention of the telescope."},{"startTime":2881.38,"endTime":2885.16,"body":"It was terrific to have one"},{"startTime":2881.38,"endTime":2885.16,"body":"in the neighboring galaxy,"},{"startTime":2885.16,"endTime":2887.23,"body":"in the Large Magellanic Cloud,"},{"startTime":2887.23,"endTime":2890.92,"body":"just downhill from the Tarantula Nebula,"},{"startTime":2890.92,"endTime":2893.47,"body":"with Supernova 1987A,"},{"startTime":2893.47,"endTime":2898.47,"body":"but there's so many questions"},{"startTime":2893.47,"endTime":2898.47,"body":"that that supernova raised"},{"startTime":2898.57,"endTime":2900.19,"body":"that we really want to get answers"},{"startTime":2900.19,"endTime":2902.143,"body":"by studying for the next one."},{"startTime":2903.52,"endTime":2907.45,"body":"As you may know from my third"},{"startTime":2903.52,"endTime":2907.45,"body":"lecture as Gresham professor,"},{"startTime":2907.45,"endTime":2909.91,"body":"I did talk quite a lot about black holes,"},{"startTime":2909.91,"endTime":2911.68,"body":"which are the endpoint"},{"startTime":2911.68,"endTime":2915.85,"body":"of the central, compact"},{"startTime":2911.68,"endTime":2915.85,"body":"core of a supernova"},{"startTime":2915.85,"endTime":2918.73,"body":"of the most massive stars,"},{"startTime":2918.73,"endTime":2921.823,"body":"and I love studying how black"},{"startTime":2918.73,"endTime":2921.823,"body":"holes interact with matter."},{"startTime":2922.78,"endTime":2925.0,"body":"That motivated the network of telescopes"},{"startTime":2925.0,"endTime":2926.83,"body":"that I set up around the world,"},{"startTime":2926.83,"endTime":2928.96,"body":"called the Global Jet Watch,"},{"startTime":2928.96,"endTime":2930.79,"body":"separated in longitude"},{"startTime":2930.79,"endTime":2933.25,"body":"so there's always one of them in darkness"},{"startTime":2933.25,"endTime":2935.95,"body":"precisely to be able"},{"startTime":2933.25,"endTime":2935.95,"body":"to keep the watch going"},{"startTime":2935.95,"endTime":2939.04,"body":"on variable phenomena such as explosions,"},{"startTime":2939.04,"endTime":2942.22,"body":"such as collisions,"},{"startTime":2939.04,"endTime":2942.22,"body":"such as merging events,"},{"startTime":2942.22,"endTime":2946.213,"body":"such as jets squirting out of"},{"startTime":2942.22,"endTime":2946.213,"body":"the vicinity of black holes."},{"startTime":2947.14,"endTime":2949.06,"body":"There are many different facets"},{"startTime":2949.06,"endTime":2951.73,"body":"to the astrophysics research that I can do"},{"startTime":2951.73,"endTime":2953.62,"body":"because of the Global Jet Watch,"},{"startTime":2953.62,"endTime":2954.76,"body":"and one of them"},{"startTime":2954.76,"endTime":2959.76,"body":"is preparing for the next"},{"startTime":2954.76,"endTime":2959.76,"body":"galactic supernova explosion."},{"startTime":2960.19,"endTime":2962.23,"body":"We've planned and discussed protocols"},{"startTime":2962.23,"endTime":2965.92,"body":"for what to do when that event happens."},{"startTime":2965.92,"endTime":2969.36,"body":"So that's a little description,"},{"startTime":2965.92,"endTime":2969.36,"body":"that lecture there,"},{"startTime":2969.36,"endTime":2970.57,"body":"of the Global Jet Watch"},{"startTime":2970.57,"endTime":2973.12,"body":"and the science that motivates it,"},{"startTime":2973.12,"endTime":2976.15,"body":"how matter behaves in the"},{"startTime":2973.12,"endTime":2976.15,"body":"vicinity of black holes,"},{"startTime":2976.15,"endTime":2979.57,"body":"but this is the network of telescopes."},{"startTime":2979.57,"endTime":2981.34,"body":"There are five of them, as I say,"},{"startTime":2981.34,"endTime":2984.37,"body":"separated in longitude around the planet,"},{"startTime":2984.37,"endTime":2987.7,"body":"one at each end of Australia,"},{"startTime":2984.37,"endTime":2987.7,"body":"one in rural Southern India,"},{"startTime":2987.7,"endTime":2990.97,"body":"one in South Africa, and one in Chile,"},{"startTime":2990.97,"endTime":2992.2,"body":"and so between them,"},{"startTime":2992.2,"endTime":2995.02,"body":"these telescopes can keep the watch going."},{"startTime":2995.02,"endTime":2998.47,"body":"I've studied quite a"},{"startTime":2995.02,"endTime":2998.47,"body":"few nova explosions now"},{"startTime":2998.47,"endTime":2999.76,"body":"with these telescopes,"},{"startTime":2999.76,"endTime":3000.93,"body":"and we've had a ball,"},{"startTime":3000.93,"endTime":3002.55,"body":"we've learned a lot."},{"startTime":3002.55,"endTime":3007.05,"body":"Some of the ways in which"},{"startTime":3002.55,"endTime":3007.05,"body":"those objects change"},{"startTime":3007.05,"endTime":3009.96,"body":"and their spectra change with time"},{"startTime":3009.96,"endTime":3011.7,"body":"is very rapid,"},{"startTime":3011.7,"endTime":3014.52,"body":"it's timescales of less than an hour,"},{"startTime":3014.52,"endTime":3017.16,"body":"and it's only if you"},{"startTime":3014.52,"endTime":3017.16,"body":"can keep the watch going"},{"startTime":3017.16,"endTime":3018.96,"body":"with such telescopes"},{"startTime":3018.96,"endTime":3023.96,"body":"that you can hope to study and"},{"startTime":3018.96,"endTime":3023.96,"body":"investigate in detail events"},{"startTime":3024.6,"endTime":3028.68,"body":"on the timescales on which"},{"startTime":3024.6,"endTime":3028.68,"body":"they actually happen."},{"startTime":3028.68,"endTime":3031.65,"body":"So I thought you might like to see"},{"startTime":3031.65,"endTime":3035.22,"body":"how observations happen in practice."},{"startTime":3035.22,"endTime":3038.07,"body":"For our normal observations,"},{"startTime":3038.07,"endTime":3041.433,"body":"everything happens"},{"startTime":3038.07,"endTime":3041.433,"body":"really quite robotically."},{"startTime":3042.51,"endTime":3045.81,"body":"So we have a whole bunch of cameras"},{"startTime":3045.81,"endTime":3047.61,"body":"which look out on the night sky,"},{"startTime":3047.61,"endTime":3049.32,"body":"we have a narrow field finder-scope,"},{"startTime":3049.32,"endTime":3052.623,"body":"We have an all-sky camera,"},{"startTime":3049.32,"endTime":3052.623,"body":"updated since that one there,"},{"startTime":3053.46,"endTime":3054.51,"body":"and all those cameras"},{"startTime":3054.51,"endTime":3058.41,"body":"help us to be sure of"},{"startTime":3054.51,"endTime":3058.41,"body":"what the surroundings are,"},{"startTime":3058.41,"endTime":3059.94,"body":"are there any clouds rocking up,"},{"startTime":3059.94,"endTime":3061.35,"body":"do we need to be careful"},{"startTime":3061.35,"endTime":3064.47,"body":"to protect the optical"},{"startTime":3061.35,"endTime":3064.47,"body":"equipment and the electronics"},{"startTime":3064.47,"endTime":3065.85,"body":"from water."},{"startTime":3065.85,"endTime":3068.94,"body":"These are all the astronomical"},{"startTime":3065.85,"endTime":3068.94,"body":"cameras appearing,"},{"startTime":3068.94,"endTime":3071.73,"body":"and they take data in different ways"},{"startTime":3071.73,"endTime":3075.513,"body":"according to the investigations"},{"startTime":3071.73,"endTime":3075.513,"body":"that were taking place."},{"startTime":3076.95,"endTime":3081.66,"body":"The telescope acquires"},{"startTime":3076.95,"endTime":3081.66,"body":"the target robotically,"},{"startTime":3081.66,"endTime":3085.53,"body":"it takes an image half a"},{"startTime":3081.66,"endTime":3085.53,"body":"degree by half a degree"},{"startTime":3085.53,"endTime":3087.63,"body":"with a big imaging camera,"},{"startTime":3087.63,"endTime":3091.29,"body":"which we then solve for astrometrically,"},{"startTime":3091.29,"endTime":3092.7,"body":"in other words we work out"},{"startTime":3092.7,"endTime":3094.95,"body":"exactly where we're pointing in the sky,"},{"startTime":3094.95,"endTime":3096.36,"body":"and then we line up,"},{"startTime":3096.36,"endTime":3098.91,"body":"and then we can start"},{"startTime":3096.36,"endTime":3098.91,"body":"doing our spectroscopy,"},{"startTime":3098.91,"endTime":3101.16,"body":"which is up in the top-left corner,"},{"startTime":3101.16,"endTime":3105.42,"body":"that's aligning a target"},{"startTime":3101.16,"endTime":3105.42,"body":"with an optical fiber"},{"startTime":3105.42,"endTime":3108.06,"body":"that takes the light"},{"startTime":3105.42,"endTime":3108.06,"body":"collected by the telescope"},{"startTime":3108.06,"endTime":3110.25,"body":"down to the instrument"},{"startTime":3108.06,"endTime":3110.25,"body":"called the spectrograph,"},{"startTime":3110.25,"endTime":3112.2,"body":"which splits up the light."},{"startTime":3112.2,"endTime":3115.95,"body":"This is what happens when"},{"startTime":3112.2,"endTime":3115.95,"body":"we know about the targets,"},{"startTime":3115.95,"endTime":3118.59,"body":"but when a supernova goes bang,"},{"startTime":3118.59,"endTime":3122.31,"body":"how do we know where"},{"startTime":3118.59,"endTime":3122.31,"body":"to point the telescope,"},{"startTime":3122.31,"endTime":3125.22,"body":"what is our warning going to be"},{"startTime":3125.22,"endTime":3127.68,"body":"that a supernova explosion"},{"startTime":3127.68,"endTime":3131.34,"body":"is about to be observable from Earth?"},{"startTime":3131.34,"endTime":3133.86,"body":"Well think back to the neutrinos."},{"startTime":3133.86,"endTime":3137.61,"body":"Neutrinos, that I mentioned"},{"startTime":3133.86,"endTime":3137.61,"body":"at the start of my talk,"},{"startTime":3137.61,"endTime":3140.4,"body":"herald, by a few hours,"},{"startTime":3140.4,"endTime":3143.13,"body":"probably, according to different models,"},{"startTime":3143.13,"endTime":3147.54,"body":"the onset of optical"},{"startTime":3143.13,"endTime":3147.54,"body":"emission, optical light"},{"startTime":3147.54,"endTime":3149.7,"body":"from a supernova explosion,"},{"startTime":3149.7,"endTime":3154.26,"body":"so if we hear from our"},{"startTime":3149.7,"endTime":3154.26,"body":"neutrino physics colleagues"},{"startTime":3154.26,"endTime":3157.23,"body":"that they've got a sudden spike"},{"startTime":3157.23,"endTime":3159.72,"body":"in a particular direction in the sky,"},{"startTime":3159.72,"endTime":3162.09,"body":"we are going to start exploring."},{"startTime":3162.09,"endTime":3164.25,"body":"And the way in which we will explore is,"},{"startTime":3164.25,"endTime":3166.59,"body":"so, neutrino physicists are lovely"},{"startTime":3166.59,"endTime":3167.64,"body":"and neutrinos are super,"},{"startTime":3167.64,"endTime":3169.32,"body":"but they're really slippery,"},{"startTime":3169.32,"endTime":3171.72,"body":"and you don't get directionality"},{"startTime":3171.72,"endTime":3173.67,"body":"from wherever you point your telescope,"},{"startTime":3174.6,"endTime":3178.32,"body":"so we could get an approximate position"},{"startTime":3178.32,"endTime":3181.35,"body":"that's only good to, say, 10 degrees."},{"startTime":3181.35,"endTime":3183.54,"body":"At this point, we will be using"},{"startTime":3183.54,"endTime":3187.23,"body":"the whole arsenal of"},{"startTime":3183.54,"endTime":3187.23,"body":"cameras at our disposal"},{"startTime":3187.23,"endTime":3188.16,"body":"in each observatory"},{"startTime":3188.16,"endTime":3192.66,"body":"to try and find out the optical"},{"startTime":3188.16,"endTime":3192.66,"body":"location of our telescopes"},{"startTime":3192.66,"endTime":3193.98,"body":"with, for example,"},{"startTime":3193.98,"endTime":3196.23,"body":"that narrow field finder-scope,"},{"startTime":3196.23,"endTime":3198.27,"body":"we can do a manual acquisition,"},{"startTime":3198.27,"endTime":3200.1,"body":"forget robotic acquisition,"},{"startTime":3200.1,"endTime":3202.23,"body":"that's great for normal operations,"},{"startTime":3202.23,"endTime":3205.14,"body":"but when we've got to"},{"startTime":3202.23,"endTime":3205.14,"body":"manually steer the telescope"},{"startTime":3205.14,"endTime":3207.3,"body":"to find an object that's"},{"startTime":3205.14,"endTime":3207.3,"body":"suddenly brightening,"},{"startTime":3207.3,"endTime":3208.38,"body":"and suddenly brightening,"},{"startTime":3208.38,"endTime":3210.3,"body":"and getting brighter and brighter,"},{"startTime":3210.3,"endTime":3212.52,"body":"we need to be able to act quickly,"},{"startTime":3212.52,"endTime":3214.047,"body":"and we think we might be ready for that,"},{"startTime":3214.047,"endTime":3215.823,"body":"and we're looking forward to it."},{"startTime":3217.17,"endTime":3219.6,"body":"These are some of the auxiliary cameras"},{"startTime":3219.6,"endTime":3221.85,"body":"that will aid us in that endeavor."},{"startTime":3221.85,"endTime":3224.07,"body":"These are commensal cameras"},{"startTime":3224.07,"endTime":3228.78,"body":"that support the main light"},{"startTime":3224.07,"endTime":3228.78,"body":"collection of the telescopes,"},{"startTime":3228.78,"endTime":3231.36,"body":"and here they are shown"},{"startTime":3228.78,"endTime":3231.36,"body":"with some schoolgirls"},{"startTime":3231.36,"endTime":3232.59,"body":"at my India telescope"},{"startTime":3232.59,"endTime":3234.06,"body":"for scale."},{"startTime":3234.06,"endTime":3239.06,"body":"These mini telescopes,"},{"startTime":3234.06,"endTime":3239.06,"body":"these commensal cameras"},{"startTime":3239.79,"endTime":3242.55,"body":"have a much wider field"},{"startTime":3239.79,"endTime":3242.55,"body":"than the main telescope,"},{"startTime":3242.55,"endTime":3245.43,"body":"and so they'll be"},{"startTime":3242.55,"endTime":3245.43,"body":"capturing the light curves"},{"startTime":3245.43,"endTime":3249.3,"body":"of wherever the proto-supernova,"},{"startTime":3249.3,"endTime":3251.52,"body":"and then the fully-blown supernova is"},{"startTime":3251.52,"endTime":3252.99,"body":"wherever it is on the chip,"},{"startTime":3252.99,"endTime":3254.97,"body":"so we'll capture the light curves"},{"startTime":3254.97,"endTime":3258.36,"body":"at the same time as we"},{"startTime":3254.97,"endTime":3258.36,"body":"get ourselves lined up"},{"startTime":3258.36,"endTime":3261.033,"body":"to be able to do spectroscopy as well,"},{"startTime":3261.96,"endTime":3263.43,"body":"so we're really looking forward"},{"startTime":3263.43,"endTime":3266.76,"body":"to the next galactic supernova."},{"startTime":3266.76,"endTime":3270.51,"body":"It may not happen in the"},{"startTime":3266.76,"endTime":3270.51,"body":"lifetime of anyone in this room,"},{"startTime":3270.51,"endTime":3271.8,"body":"but if it does happen,"},{"startTime":3271.8,"endTime":3274.74,"body":"I think, I hope that we are ready,"},{"startTime":3274.74,"endTime":3277.143,"body":"and I'll be delighted to"},{"startTime":3274.74,"endTime":3277.143,"body":"tell you all about it."},{"startTime":3278.52,"endTime":3281.7,"body":"So big stars end with a bang,"},{"startTime":3281.7,"endTime":3285.703,"body":"it's really important to appreciate this."},{"startTime":3285.703,"endTime":3288.24,"body":"A supernova explosion"},{"startTime":3288.24,"endTime":3292.44,"body":"involves the most"},{"startTime":3288.24,"endTime":3292.44,"body":"almighty release of energy"},{"startTime":3292.44,"endTime":3294.78,"body":"over very rapid timescales,"},{"startTime":3294.78,"endTime":3296.73,"body":"as you saw from the numbers"},{"startTime":3296.73,"endTime":3299.22,"body":"in the context of Kepler's Supernova,"},{"startTime":3299.22,"endTime":3302.73,"body":"the one that went bang in 1604."},{"startTime":3302.73,"endTime":3305.4,"body":"So massive stars, as I've indicated,"},{"startTime":3305.4,"endTime":3308.16,"body":"are important for life itself,"},{"startTime":3308.16,"endTime":3309.75,"body":"and when they end,"},{"startTime":3309.75,"endTime":3311.88,"body":"they do so not with a whimper,"},{"startTime":3311.88,"endTime":3314.43,"body":"but most assuredly with a bang."},{"startTime":3314.43,"endTime":3316.103,"body":"Thank you very much."},{"startTime":3316.103,"endTime":3319.103,"body":"(audience applauds)"}]}