How Do We Know That Galaxy Clusters Contain a Lot

question 89

Multiple Choice

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.

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