A galaxy cluster consists of 1,000 galaxies within a radius of 2.5 Mpc,traveling at a typical velocity of 1,000 km/s.If the average stellar mass of a cluster galaxy is 10¹¹ M_Sun,what fraction of the cluster's mass is NOT stellar? A) 5/6 B) 9/10 C) 1/2 D) 1/10

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Quizplus · Accepted Answer

The total stellar mass is 10¹¹ M_Sun per galaxy times 1,000 galaxies, which equals 10¹⁴ M_Sun. The total mass of the cluster can be estimated using the virial theorem, which relates the velocity dispersion to the total mass. The mass is approximately 10¹⁵ M_Sun. The fraction of mass that is not stellar is (10¹⁵ - 10¹⁴) / 10¹⁵ = 9/10.

A Galaxy Cluster Consists of 1,000 Galaxies Within a Radius