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.

Question

Quizplus · Accepted Answer

The rapid variation in brightness over a period of a few days implies that the source is compact, with changes occurring across the entire source in a short time. This suggests the source is no more than a few light-days in diameter, as light would take at most a few days to travel across the source, allowing the observed changes to occur almost simultaneously throughout.

Suppose We Observe a Source of X-Rays That Varies Substantially