Wednesday, August 8, 2007

Blinding You With Science: Gravity Kills

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Last night's episode of "The Universe" -- you know, the History Channel show and primary source of my astronomical knowledge -- was about the life and death of stars.

Stars are born when gravity pulls a cloud of hydrogen together into a ball. Gravity would immediately collapse this ball of hydrogen together into an extremely dense nugget of matter; however, the very act of gravity pulling hydrogen together into a ball creates heat that synthesizes hydrogen into helium molecules. This synthesis (aka "nuclear fusion") creates an "outward" force to balance the "inward" force of gravity so that the star ceases to contract. (Imagine arm wrestling someone of equal strength: both of you are applying great force, but no one's arm is going anywhere.) This period of stasis in a star's life is called the "main sequence" -- our own sun is currently in the "main sequence" phase of its life.

Eventually, though, all of the hydrogen molecules in the core of the star are turned into helium, and then things get crazy. If the star is quite large (nine solar masses or more), then there is enough energy for its new helium core to fuse, which creates carbon, which fuses together to create oxygen, which fuses together to create neon, and then silicon and sulfur and iron. At this point, the star is at the end of its red giant phase, and no more elements can be synthesized because, unlike the lighter elements preceding it, iron does not produce energy when it fuses together. Rather, iron consumes energy when it fuses together, and at a certain size the iron core can no longer support its own mass and collapses from the size of our Sun to the size of Manhattan in half a second. This sudden collapse creates a massive shockwave that explodes the rest of the star's material into space -- a supernova. The energy released during a supernova synthesizes the heaviest element of the former star -- iron -- into all of the remaining heavier elements in the universe.

That means calcium, silver, gold, everything. Everything heavier than iron in all of existence was synthesized from the material of an exploding star.

Deal with that.

So, in sum:

1. Everything around us is a product of gravity's force on hydrogen.

2. No finite amount of hydrogen can withstand the force of gravity.

3. Gravity always wins, and produces a lot of cool stuff.

So where did gravity come from?

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