black+hole

Black holes There are popular myths concerning black holes, many of them perpetuated by Hollywood. Television and movies have portrayed then as time-traveling tunnels to another dimension, cosmic vacuum cleaners sucking up everything in sight, and so on. It can be said that black holes are really just the evolutionary end point of massive stars. But somehow, this simple explanation makes them no easier to understand or less mysterious.

Black holes: What are they? Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If a star hat massive or larger undergoes a supernova explosion, it may leave behind a fairly massive burned out stellar remnant. With no outward forces to oppose gravitational forces, the remnant will collapse in on itself. The star eventually collapses to the point of zero volume and infinite density, creating what is known as a "singularity". As the density increases, the path of light rays emitted from the star are bent and eventually wrapped irrevocably around the star. Any emitted photons are trapped into an orbit by the intense gravitatonal filed; they will will never leave it. Becauseno light escapes after the star reached this infinite density, it is called a black hole.

But contrary to popular myth, a black hole the same mass, the earth's orbit around the Sun would be unchanged. (Of course the earth's temperature would change,and there would be no solar wind or solar magnetic storm affecting us.) At this radius, the escape speed is equal to the speed of light, and once light passes through, even it cannot it cannot escape. The Schwarzschild radius can be can be calculated using the equation for escape speed.