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We've already talked about the life cycles of stars, roughly the same mass as our sun, give or take a little bit

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what i want to do with this video is talk about more massive stars - massive stars.

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When i'm talking about massive stars, I'm talking about stars that have masses great than nine times the sun.

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So the general idea is exactly the same, you're going to start off with this huge cloud of mainly hydrogen,

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and now the cloud is going to have to be bigger than the clouds that condensed to form stars, like our Sun.

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We are going to start with that, and eventually gravity is going to pull it together, and the core of it is going to get hot and dense enough

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for hydrogen, to ignite - for hydrogen to start fusing.

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And it is now fusing. Hydrogen Fusion. You now have hydrogen fusion in the middle so it's ignited and around it you have

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the other material of the cloud, so the rest of the Hydrogen, and now it's so heated it's, really a plasma kind of a soup of electrons

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and nucleuses as opposed to well formed atoms, especially close to the core.

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So now you have hydrogen fusion, we saw this happen around 10 million Kelvin

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and I want to make it very clear, since we are talking about more massive stars, even at this stage,

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there is going to be more gravitational pressure, even at this stage, during the main sequence of the star

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because it is more massive, so this is going to burn faster and hotter.

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So this will be faster and hotter than something the mass of our Sun. And so, even this stage is going to happen over a much

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shorter period of time than a star the mass of our sun. Our Sun's life is going to be 10 or 11 billion

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total years, here we are going to be talking about things in the 10s of millions of years, so the factor

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of 1000x shorter life span. But anyway, let's think about what happens

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and so far just the pattern of what happens is going to happen faster because we have more pressure,

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more gravity, more temperature, but its going to happen in pretty much the same way as what we saw in the star the mass of the sun.

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Eventually, that hydrogen is going to fuse into a helium core

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that is going to have a hydrogen shell around it - a hydrogen fusion shell - around it.

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then you have the rest of the star around that - so let me label it.

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This right here is our helium core

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and more and more helium is going to be built up as this hydrogen in the shell fuses,

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and this is in a star the mass of our sun,

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this is when it starts to become a red giant because this core is starting to get denser, and denser,

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and denser as more, and more helium is produced

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and as it gets denser, and denser, and denser,

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there is more and more gravitational pressure

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being put on this hydrogen shell out here where we have fusion still happening

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and that is going to release more outward energy to push out the radius of the actual star

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but then when you fast forward there - so the general process - and we're going to see this as the star gets more and more massive,

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is we are going to have heavier and heavier elements forming in the core

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those heavier and heavier elements as the star gets denser and denser

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will eventually ignite kind of supporting the core,

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but because the core itself is getting denser and denser, and denser, the material is getting pushed further and further out with more and more energy.

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Although if the star is massive enough its not going to be pushed out as far

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as you would have with a red giant as you would have in a red giant, with kind of a sun-like star

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but let's just think about how this pattern is going to continue

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so eventually that helium, is going to - once it gets dense enough

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its going to ignite and its going to fuse into carbon and your going to have a carbon core forming

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so that is carbon core, around that you have a helium core, and near the center of the helium core,

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you have a shell of helium fusion turning into carbon, making that carbon core denser and hotter

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and then around that you have hydrogen fusion, and then around that you have the rest of the star.

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And so this process is going to keep continuing

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eventually that carbon is going to start fusing,

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and you're going to have heavier and heavier elements formed of course

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this is a depiction off of Wikipedia of a fairly mature massive star

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and you keep forming these shells of heavier and heavier elements

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and cores of heavier and heavier elements until eventually you get to iron

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and in particular we are talking about

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iron-56 - iron with an atomic mass of 56.

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Here on this periodic table, that 26 is its atomic number - its how many protons it has.

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56 is viewed as a count of protons and neutrons

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although its not exact,

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but at this point, the reason why you stop here is that you cannot get energy by fusing iron.

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Fusing iron into heavier elements beyond iron actually requires energy

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so it would actually be an endothermic process.

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So to fuse iron won't help support the core.

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So just to be very clear, this is how the heavy elements actually formed

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we started with hydrogen

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hydrogen fusing in to helium, helium fusing in to carbon, and then all of these things

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in various combinations, and i won't go into all the details, are fusing heavier and heavier elements:

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neon, oxygen, and you see it right over here -

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silicon - and these aren't the only elements forming, but these are kind of the main core elements forming

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but along the way you have all this other stuff, lithium, beryllium, boron,

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all of this other stuff is also forming.

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So this is how you form elements up to iron 56.

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And also this is actually how you can form up to nickel 56 just to be exact.

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There will also be some nickel 56

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which has the same mass as iron56

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just has two fewer neutrons and two more protons

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so its nickel 56, will also form, can also be a nickel-iron core

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but that's about how far a start can get regardless of how massive it is

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at least by going thru traditional fusion, thru the traditional ignition mechanism.

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What i want to do is leave you there,

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just so you can think about what might happen next now that we can't fuse this

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star anymore and what we are actually going to see is it will Supernova.