Question on Black Holes.

Originally posted by darklanser
I have always wondered why they say "Nothing can escape a Black Hole", when in reality, there are lots of things escaping a Black Hole. Energy waves, radio waves, x-rays....etc. If such an object had the power to pull in everything, why can these forms of energy escape? Does this negate the Unified Field theory?

Nothing escapes once IN a blackhole. That is, once inside the event horizon. Everything disscussed in this thread are thing comming from just outside the horizon. As thing fall into the hole they discharge other things outward fast enough to avoid crossing the horizon.

Originally posted by darklanser
I have always wondered why they say "Nothing can escape a Black Hole", when in reality, there are lots of things escaping a Black Hole. Energy waves, radio waves, x-rays....etc. If such an object had the power to pull in everything, why can these forms of energy escape? Does this negate the Unified Field theory?

Well, I don't know how you got the idea radio waves and x-rays escape black holes, because they don't. No electromagnetic radiation, whether it is visible light, radio or x-rays, can leave the horizon of a black hole. The gravity is simply to large.

I don't know about energy waves, because I don't know what those are. Do you know electromagnetic radiation, which carries energy? Or maybe gravitational waves, which also carry energy?

The only way energy can escape from a black hole is through Hawking radiation. Normally, all over space pairs of virtual particles are created and destroy eachother every second. Near the event horizon however, it is possible that one of such a pair gets sucked into the black hole, while the other escapes. The escaping particle is no longer virtual and needs to gets it's energy from somewhere, in this case the gravity of the black hole. This way a black hole can also 'evaporate'.

X-Rays

However, if a black hole passes through a cloud of interstellar matter, or is close to another "normal" star, the black hole can accrete matter into itself. As the matter falls or is pulled towards the black hole, it gains kinetic energy, heats up and is squeezed by tidal forces. The heating ionizes the atoms, and when the atoms reach a few million degrees Kelvin, they emit X-rays. The X-rays are sent off into space before the matter crosses the Schwarzschild radius and crashes into the singularity. Thus we can see this X-ray emission.