If a black hole is truly black and has an escape velocity greater than the speed of light such that no light can escape it,where do the X-rays come from in the black hole candidates so far identified?
A) From stars behind the black hole,whose light is focused and concentrated by gravitational focusing to the point where it becomes X-ray radiation
B) The black hole is only black to visible radiation traveling at the speed of light,but because X-rays travel faster than the speed of light,they can escape.
C) From the normal star accompanying the black hole,its ordinary light being blueshifted into the X-ray spectral region by the intense gravity of the black hole
D) From the matter surrounding the black hole,which is highly condensed and hence very hot

Question

Quizplus · Accepted Answer

X-rays are emitted from the matter surrounding the black hole, which is heated to extremely high temperatures as it is pulled towards the black hole's event horizon. This matter is often in the form of an accretion disk, composed of gas and dust that is spiraling towards the black hole. Friction and collisions within the disk cause it to heat up, emitting X-rays that can be detected by telescopes. The black hole itself is still black, as no light or radiation can escape its event horizon.

If a Black Hole Is Truly Black and Has an Escape