How did astronomers determine that elliptical galaxies are composed mostly of dark matter?
A) They measured X-ray emission from hot gas gravitationally bound to the galaxies.
B) They measured the rotation rates of gas as a function of distance from the centers of the galaxies.
C) They measured the amount of gravitational pull elliptical galaxies have on companion galaxies.
D) They assumed that the proportion of dark matter was roughly the same as in spiral galaxies.

Question

Quizplus · Accepted Answer

Astronomers measured X-ray emissions from hot gas gravitationally bound to elliptical galaxies, which indicated the presence of a significant amount of unseen mass, attributed to dark matter.

How Did Astronomers Determine That Elliptical Galaxies Are Composed Mostly