If you observed that at the centers of some galaxies there were objects emitting lots of X-rays or there was gas in rapid motion, you might conclude that these galaxies:
A) are very old
B) contain many white dwarfs
C) have different physics than on the Earth
D) are rotating quickly
E) contain black holes

Question

Quizplus · Accepted Answer

The presence of objects emitting lots of X-rays or gas in rapid motion at the centers of galaxies suggests the presence of black holes. Black holes can emit X-rays due to the immense amount of energy released as matter falls into the black hole's gravitational field, and gas can be observed in rapid motion around black holes due to the strong gravitational pull.

If You Observed That at the Centers of Some Galaxies