A disk of gas orbits a supermassive black hole.What can astronomers use to determine the mass of the black hole from the properties of this disk?

Question

Quizplus · Accepted Answer

By observing the Doppler shift of the gas disk, astronomers can determine the speed at which the gas is orbiting the black hole. From this, they can infer the mass of the black hole using Kepler's Third Law. Therefore, the best choice is B (the Doppler shift). The other options (A, C, and D) are not applicable for determining the mass of the black hole from the properties of the gas disk.

A Disk of Gas Orbits a Supermassive Black Hole