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

Question

Quizplus · Accepted Answer

The X-rays detected from black hole candidates originate from the accretion disk of matter surrounding the black hole. This matter is heated to extremely high temperatures due to gravitational forces as it spirals into the black hole, emitting X-rays before crossing the event horizon.

If a Black Hole Is Truly Black and the Escape