all right part three the final part in the first part we did the lifecycle of red dwarfs in the second part we did the lifecycle of low-mass stars now we're gonna finish up with the lifecycle of high mass stars now just like the other ones again the high mass star lifecycle starts with the protostar stage and then the main sequence stage where you are fusing hydrogen in the core the only difference again is that the high mass stars take even less time to go through these stages because of the added pressure from the gravity now here we go during the main sequence just like on every other star a high mass star is going to be fusing hydrogen and just like every other star the main sequence will end when the hydrogen in the core runs out now after the main sequence a high mass star is going to be able to fuse way more things than the low mass stars could and that's because a high mass star with its extra gravity is able to squeeze its core tighter and therefore produce higher temperatures inside the core so they confuse bigger and bigger hel elements now remember you need a higher and higher temperature to fuse bigger and bigger elements because it's harder and harder to fuse an element the more protons it has in its in its nucleus now so then on this chart I'm about to show you I'm going to show you the other things that confuse in a low or in a high mass star I am NOT going to draw little F on any of my diagrams to show what's fusing because everything that I draw in these diagrams is fusing unless I otherwise say so during the main sequence again hydrogen fusing in the core so the core would just be drawn like this that's just the core not the whole star we're drawing here I'm only drawing the core so the core has hydrogen fusing now after hydrogen fusion fuses when it runs out fusion turns off for a moment and the core shrinks and makes the core temperature go up until the point where helium confused next so the helium fusing starts the next stage whose name I will write up here in just a second so after the main sequence the first thing that fuses is helium now just like in the low mass stars when that's happening we're going to have a shell around the core where hydrogen is fusing and that's because the higher temperature in the core makes the area around the core much hotter as well to the point where the hydrogen confused there too now it's not the entire star that's fusing here just the core and a small shell around the core so helium fusion hydrogen fusion the helium will fuse until it runs out and the thing you make out of helium is a bunch of carbon and oxygen so the next thing that will fuse after helium is carbon when the helium runs out the core shrinks gets hotter until the carbon confused when the carbon is fusing because the core is hotter you gain an extra shell every time a fusion turns off in the core you gain a shell for it in the next part of the stage so here when carbon is fusing we have a shell for hydrogen and helium around it just notice that this is the same order that things fused as the star went through it's life now when the core carbon runs out it's going to the core is going to shrink and get hotter until you could fuse something else now notice I'm not telling you exactly what we make out of carbon because when we fuse carbon we make a whole bunch of other things and one of those things is the next thing that will fuse and that's neon so if we're looking so far in this stage we fused helium and then carbon and then neon now when we start to fuse neon in the core now notice I've got neon in the middle and I've got a new carbon shell from the last fusion in addition to the helium shell and the hydrogen shell that we've had all along now the Neely sorry the neon will fuse until it runs out when it runs out the core will shrink it will get hotter until we confuse oxygen the oxygen will fuse until it can retrun zout then the next thing that will fuse will be silicon so when we're fusing all of these things when we're fusing silicon we have a shell for every one of these other things all at the same time that means we refusing a lot of things at once during this stage so that means our luminosity is going to go way up and if the luminosity goes way up it's gonna push the rest of the star outward way more than ever before and that means that this type of star will get extremely big after the main sequence and that's why we call this stage the supergiant stage so the stage after the main sequence in which a high-mass star fuses a whole lot of different things is called the supergiant stage so I'm going to write that down up here give me just a second to pop this pin open here we go so supergiant okay supergiant stage so during the main sequence we've used hydrogen and then after that during the supergiant phase we fused these things in order so make sure you know this order now when the silicon is done fusing it produces iron so the symbol for iron unfortunately is F II and I'll write iron down next to it I earn and when that happens the the star is no longer a supergiant when the core runs out of silicon and makes iron the supergiant stage is over and that's because a core made of iron is a giant problem for the star and the reason for that has to do with the periodic table now it turns out that all of these other elements that we've we've drawn here all of these other elements are smaller than iron they're smaller than iron and if you fuse hydrogen remember we said that you get light out that's a form of energy coming out the same thing is true for helium you get light out for carbon you get light out neon you get light out oxygen silicon you get light out for any element that's smaller than iron when you fuse it you get energy out for anything iron or bigger you actually have to put energy in to get it to fuse however Fusion was the energy source in a star so this core is not going to fuse it needs energy to fuse but fusion is where a star's energy comes from so you can't power your in fusion with the fusion that doesn't make sense you can't power your car with your car that doesn't make sense so as soon as the core becomes iron it will never be able to fuse that iron no matter how hot it gets its core so no matter how big the quarter though that this star is iron is the end of the road now that means that the core of the star at this point will not be able to fuse just as an aside at this point the supergiant will be as big as it possibly can be and when I say as big as it can possibly be some of these super Giants will actually be bigger than the orbit of Neptune the farthest planet from the Sun these these stars are bigger essentially than the planet part of our solar system giant giant giant giant giant giant that's why it's super giant now back to the iron when that core becomes iron it can't fuse it so what does gravity do well it crushes the iron it crushes the core of the star and if that happens if we look over here if this course suddenly crushes it'll crush so quickly that the material will rebound off of itself and then ricochet back out through the star that's not good for a star if this material ricochets back outward it's going to literally explode the rest of the star so the most of the star is going to explode off in what we call a supernova so right at the end of the supergiant stage in about 10 seconds a supernova happens now what does this supernova look like well your book has a couple of pictures of them so here we go so if you look right here back in 1987 September of 1987 it was the first time that we predicted accurately that when a star was going to explode which is a big indication that we were right about this whole process the whole life cycle of these stars so we predicted that that star that the arrow is pointing to would explode and right when we thought it would it produced a giant flash of light as you can see in this picture now that slowly faded and you can't see it anymore today but supernovae are insane explosions if if our son could supernova but remember it can't because we're not a high mass star but if it did if our Sun supernova or if our son died in a supernova then you would receive more explosive force on your body than if you took a average atomic bomb pressed it to your face and then blew it up that atomic bomb explosion in your face would be less of an explosion than the Sun going supernova 93 million miles away that is how big a supernova is and that's our Sun our Suns small it's too small to supernova the stars that do go supernova would be an even bigger explosion now the star doesn't just disappear most of the material the star explodes off all of these shells would explode off and then everything else that's around the star would it would explode off and what you're going to be left with is a giant basically a giant cloud of gas that is shot out of the supernova it's known as a supernova supernova remnant supernova remnant all right after that star explodes what's left behind is the leftover core that was originally made of iron now that leftover core can become one of two things depending on what how much material is left the first thing that can become is called a neutron star if less than two or three solar masses is left the other thing it can become is a black hole if more than two or three solar masses is leftover we'll talk about neutron stars and black holes in class so this is the complete lifecycle for high mass stars all right now a couple of things to note this supernova takes much less time to kill the star than the planetary nebula did for low mass stars a supernova takes about 10 seconds to happen even though the actual cloud that shoots out of the star can remain visible for thousands of years a planetary nebula however on a low-mass star when it slowly puffs itself to death can take thousands of years to destroy the star in the first place so it's a much gentler process supernovas are not gentle at all now the final thing I want to say about supernovas is something that's a little bit ironic now remember the whole reason that the supernova happened is because iron has to have an energy source in it to fuse and the star didn't have an energy source well if the star explodes an explosion is a source of energy so as soon as the star explodes the iron now has an energy source and so just for the 10 seconds that the star is exploding exploding iron will fuse now what do you make when you fuse iron you make a lot of things but here are some ecologist tell you some examples some things you make when you explode iron are gold silver platinum and uranium you may notice that those are all expensive rare things and the reason they're expensive and rare is because they're only made when a star explodes so every piece of gold and silver and platinum you've ever seen or touched or maybe are wearing right now and also sums in your computer or phone at this second that stuff shot out of an exploding star at some point which is crazy all right that's the end of this video series remember we'll talk about the dead stars white dwarfs neutron stars and black holes when we get back to class at the beginning of next week sorry for the quality of the videos I was unable to find anybody to to film them for me oh man it's dead it's okay alright see you guys next week