Wednesday, May 20, 2009

College For Free 2: The Life of a Star

The point of this blog is to tell you, if you're interested in this sort of thing, how stars are made. Intro to Stars and Galaxies was without question one of the most interesting classes I've ever taken. Some people may disagree, and I don't really understand that. For example: During the lecture on how black holes form, I saw people walking out of the room.
Like, are you serious? Haven't you been wondering your entire life exactly what black holes are and how they exist? Because I sure have.
Bottom line: If you've got more important things to do than learn how the universe works, you probably don't have anything in common with me.

Stars form out of things called Giant Molecular Clouds. These clouds are composed mostly of hydrogen, helium, and trace amounts of other elements, and if you know anything about space, you'll know that this is the composition of just about everything out there. It is probably important to mention how big these clouds are, and man are they big. Like, completely unimaginably big. They can be hundreds of light years across. To give you some scope, our galaxy is about 100,000 light years across. Hm, maybe that doesn't actually help.
Anyways, the Giant Molecular Clouds that form stars are only those that are the coldest and densest. What's interesting about this is that by "densest" I mean less dense than any vacuum that we can create on Earth, even in billion dollar NASA laboratories. And by coldest, I mean 30 Kelvin, which is probably something like -400 Fahrenheit.
This is just to give you an idea of how ridiculous space is. Now, onto the actual stars.
Basically, some sort of force will cause these Giant Molecular Clouds to collapse, maybe the pulse of a dying star, maybe a passing spaceship, it doesn't take much. The clouds collapse over a period of about a few hundred thousand years and can produce as many as a hundred or a thousand new stars as gravity begins to group the elements together. The size of the star determines how long it takes for the stars to reach their complete state, which is where they spend the majority of their lives. The big guys might take as little as 50 thousand years, the smaller stars 500 million. It all depends. For the sake of the blog, we're going to focus on a big star. Mostly because I want to talk about super novas.
All stars fuse hydrogen into helium, that's where they get their energy. Stars fuse hydrogen into helium (a process that takes four hydrogen atoms and creates one helium atom, thereby losing mass and creating energy) for about 80-90% of it's life. Hydrogen fusion stops when all the hydrogen runs out, and when all the hydrogen is gone, you go from a hydrogen core to a helium core with a hydrogen shell around it. We all know what happens to smaller stars at this point. You get a red giant then a white dwarf. Whatever. Boring.
In bigger stars, the pressure and heat is intense enough that helium can continue to produce fusion energy by fusing into carbon, the third lightest element. This is when the star becomes a supergiant. So, all the helium fuses into carbon until the helium runs out, then you have a carbon core and a helium shell. As you can see from the picture at the top of this blog, this process continues through carbon, neon, oxygen, silicon and into iron.
Now, iron is what messes everything up, because iron can't fuse without stealing energy from the outer layers of star. Because of this, the iron core rapidly expands, which is putting it sort of lightly. By this, I mean it goes from being nonexistent to one and a half times the size of our sun in about 3 days. It gets sort of complicated at this point, but basically what happens is that Electron Degeneracy Pressure (a type of pressure that only exists inside of stars) forces electrons to start sort of playing musical chairs with each other. So, now these free electrons that don't have seats begin to combine with protons, which create neutrons, which create a neutron core.
The neutron core collapses from the size of one and a half times the size of our sun to the size of Kalamazoo county in a fraction of a second. The release of gravity and potential energy results in an explosive ejection of the outer layers, or a super nova, which must be so cool to watch. I wish our sun was going to super nova.
In the cores of aged supergiants, and during super nova, rare conditions called neutron capture processes occur, in which all elements heavier than iron are created. These events last for ten minutes.
In the case of larger stars, this whole process from beginning to end probably took about 10 million years, maybe longer.

Now, on this point I have more to say. I have more to say about black holes, I have more to say about the neutron capture process, I have more to say about the fact that all, ALL, elements heavier than iron (which, if you haven't noticed, is all elements not mentioned in this blog) are created during the last ten minutes of a 10 million year process.
But I'll save all that for another time, because this blog is already too long and full of science stuff.
I hope this blog does a few things for you: one is to let you know that we are all made up of all the same elements as those present in stars and outer space, and I think that's pretty cool. Two is, I hope the next time you see a gold watch or necklace or something, remember that it originated in outer space millions of years ago. Three, keep things in perspective. You are an infinitely small dot on an infinitely small dot in the infinite blackness of the universe. Don't stress out about paying your rent, it's just silly.

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