Saturday, October 6, 2007

The Universe: Star Death

Everything, even the Universe itself, must end one day. Stars have life-spans far longer than we humans, with our fleeting existences, can appreciate. Their end comes when they exhaust their supply of hydrogen fuel; and they make their exit one of several ways, depending on their mass. Here are a few possibilities for the future of the stars in our galaxy. If you want more information, check out Astronomy: A Visual Guide, by Mark A. Garlick.

Planetary Nebulae:
When small or medium-sized stars (like our sun, coincidentally) run out of fuel, the reactions begin to shut down and its core contracts. As the core grows hotter and denser, the rest of the star puffs up like a giant balloon. The star's gravity becomes so weak that it can no longer hold onto its outer layers, and they slip away into space. This shell of gas glows due to the exposed core. Nebulae come in many different forms, and astronomers don't entirely understand how this happens. Sadly, these beautiful objects don't last for long: after "only" about 10,000 years, they fade and become white dwarfs.

Supernovae:
These gigantic explosions signal the end for very massive stars. When the hydrogen reaction in its core runs out, the star suddenly buckles inward and collapses. As the object's density increases and the pressure builds, it eventually rebounds. This recoil sends out a giant series of shock waves, blowing the star to pieces. These events are often so powerful that no white dwarf "corpse" is left behind: nothing of the star remains behind. Naturally, an explosion of this magnitude tends to cause destruction across a very wide area: most of the star's orbiting planets would be destroyed in the process.

Black Holes:
What happens when gravity is so strong that nothing can escape the suface, no matter how fast or hard you throw it? These are the conditions in a black hole, a very massive star which has shattered, shrinking to a single point, so dense that nothing can escape, even light. There, the laws of physics fail to operate. If you could see one, a black hole would appear as a completely featureless black disc, surrounded by distorted images of the objects that were nearby.

White Dwarfs:
Becoming a nebula does not mark the end of a star's life. Even after the nebula has disbursed, the exposed core of the original star remains. White dwarfs are extremely dense, slowly compacted under gravity for hundreds of millions of years while the former star was consuming its last bits of fuel. White dwarfs do not shine because of nuclear reactions, but by releasing the energy stored inside them while they were still active. It can take tens of billions of years for a white dwarf to completely cool down.

A reader sent me a link to an awesome website where you can see photos of the Universe taken from the Hubble telescope. I highly recommend checking it out. Just click here.

You can also check out my previous posts on the Universe. Just click here.

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