The Last Day
For most of their lives, the stars change at a slow, steady pace. For millions or billions of years, they "fuse" the hydrogen atoms in their cores to create helium, plus lots of energy.
As they near the ends of their lives, though, the pace picks up. As they deplete their supplies of hydrogen, they consume helium, and possibly heavier elements. Their cores get hotter and denser, and their outer layers puff up like big balloons.
In the most-massive stars, the changes take place at an amazing pace.
In the last day of their lives, their cores "burn" through a succession of heavier elements, until all that's left is iron. When that happens, the core collapses to form a neutron star, or maybe even a black hole. If the core was rotating before its collapse, it spins hundreds of times faster after the collapse, generating a powerful magnetic field. The magnetic field and a strong shock wave may work together to rip through the star's outer layers, blasting them into space as a supernova - one of the most powerful events in the universe.
This only works for heavy stars - those that are at least 8 to 10 times as massive as the Sun. The gravity of such massive stars squeezes their cores tighter and tighter, making them extremely hot and dense. That provides the right conditions for the rapid-fire events during the final 24 hours - the last day in the life of a giant star.
We'll have more tomorrow.
Script by Damond Benningfield, Copyright 2005
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
|
Contact | About | Friends of McDonald | Sign up for Sky Tips
