Gamma-Ray Bursts II
A black hole is well named. Matter and energy fall in, but absolutely nothing comes out.
But the birth of a black hole is another matter. It may announce its formation with one of the biggest displays of pyrotechnics in the universe -- a gamma-ray burst. It lasts only a few moments, but it produces more energy than the Sun will generate in its entire 10 billion-year lifetime. Such an outburst is easily detectable even if it's billions of light-years away.
There are actually two classes of gamma-ray bursts. One lasts no more than a couple of seconds, and may be the result of a collision between two neutron stars; more about that tomorrow.
But the other class lasts up to a few minutes. These bursts may announce the violent death of a supermassive star, accompanied by the birth of a black hole.
In this scenario, the star can no longer produce energy in its core. Without energy to push outward, gravity pulls the core inward, so it collapses to form a black hole that's a few times as massive as the Sun.
The star's outer layers are blasted out into space, forming a supernova. If the star is spinning rapidly, though, a narrow channel may form along the star's rotation axis. Energy and matter shoot out into space along this axis, forming enormously powerful "jets" from the star's poles. And if Earth happens to line up in the direction of one of these jets, we see a gamma-ray burst -- the bright birth of a black hole.
Script by Damond Benningfield, Copyright 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.