How do we know that galaxy clusters contain a lot of mass in the form of hot gas that fills spaces between individual galaxies?
A)We infer its existence by observing its gravitational effects on the galaxy motions.
B)The hot gas shows up as bright pink in visible-light photos of galaxy clusters.
C)We can observe the frictional effects of the hot gas in slowing the speeds of galaxies in the clusters.
D)We detect this gas with X-ray telescopes.

Question

Quizplus · Accepted Answer

We detect hot gas that fills spaces between individual galaxies in galaxy clusters with X-ray telescopes. This hot gas emits X-rays due to the high temperatures, which can be detected by X-ray telescopes.

How Do We Know That Galaxy Clusters Contain a Lot