Question

Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?

A) The X-ray source is a quasar.
B) The X-ray source contains a black hole with an accretion disk.
C) The X-ray source is no more than a few light-days in diameter.
D) The X-ray source must have a strong, rapidly varying magnetic field.
E) We are seeing the rapid orbit of two stars in a binary system

Answer 1

The rapid variability in brightness of an X-ray source over a few days indicates the presence of a black hole with an accretion disk.

Step-by-step explanation:

The rapid variability in brightness of an X-ray source over a few days indicates that the source contains a black hole with an accretion disk. This is because the generation of energy in such a small region requires a great deal of mass to be confined into a small space, which can only be achieved by a black hole. In some cases, the X-rays are emitted from a region just a few times the size of the black hole event horizon.