Sunday, September 19, 2010

My (Former) Research Explained: The Foundation of Stars

Stars are awesome. They come in all sizes and colors. They can be tiny and cool (the elusive brown dwarf), they can be massive and hot (blue supergiant), they can rotate really fast and emit pulses (pulsar), they can even be so massive they pull everything into it (a black hole). The sun is an average yellow star, but it is because it is average that actually makes it so special.

If the sun were any smaller, it wouldn't emit enough energy to produce life on Earth. Conversely, if it were any bigger it would incinerate Earth. If it were any other type of star, the various types of light radiation would wreak havoc on our planet. Could you imagine a star that was massive and bright, but also bombards our planet with x-rays, gamma rays, and/or microwaves? The sun does emit this stuff, but only in very small quantities. 

Not only is the sun important, but stars are the fuel of the universe. Without stars we wouldn't have any of the elements that exist. We wouldn't have water, gold, uranium, carbon, or any elements outside of hydrogen and maybe a couple of the lighter elements. How did these elements get made? How do stars like our sun get made? What will happen when the sun dies?

Well I'm about to tell you all I can remember about the processes that govern our universe.
Everyone knows about the big bang. All the matter in the universe was compressed into one space (possibly a point) and exploded. In the first minutes of the universe as we know it, the first particles were created. Protons, neutrons, and electrons fused from smaller elementary particles. As time goes on these particles fuse to create the first atoms hydrogen and helium and possibly some other lighter elements like lithium and boron.
from http://www.ichthus.info/BigBang/intro.html
Around this time clouds of gas start coming together due to gravitational attraction and form the first stars. Since there is a lot of gas the stars are quite massive, in fact very massive. Massive stars don't live for very long (relative to smaller stars) because of the nature of the reactions that go on inside a star.

Fusion is the main process that powers a star. Gravity wants to pull all the molecules inside a star together. This attraction causes elements in the star to fuse together. Hydrogen atoms push together to become helium. This reaction releases a lot of energy (think of E=mc^2) and pushes the star outward. The forces of gravity and fusion balance each other keeping the star stable. 
from http://www.sfa-fuzija.si/fusion.htm
Because these early stars were so massive there was enough gravity to fuse hydrogen into helium, helium into lithium, lithium and rest into carbon, oxygen, nitrogen, and all those to form heavy metals and many of the elements we find here on earth. Now it requires a lot of energy to form those elements but the energy released isn't nearly as much. So when the hydrogen and helium was depleted the outward force from fusion wasn't as much and these massive stars began to collapse.

At first the collapse was a little, but then fusion couldn't keep up with gravity and this cause a massive collapse. The stars would then explode in a supernova (but I imagine at this time the stars were so large that the supernovas must have been mighty impressive compared to today's standards). The supernova would spread elements all over the universe. 

These elements would combine together to form gas clouds like I mentioned earlier, but since the universe was expanding the clouds weren't nearly as massive. This allowed for more normal sized stars to form (like our sun).
Normal? Riiiiight...
I tell you all this because the balance of gravity and fusion pressure is crucial to what happens during a star's lifespan. Small stars like our sun will have a nice, happy, long, and healthy life while massive stars will live short, violent, bloated lives (much like me!). And since I've decided to split this up into a couple of posts I'll talk more about that in the next post.


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