A star of mass 2.0 ✕ 1029 kg that is 1.8 ✕ 1020 m from the center of a galaxy revolves around that center once every 2.2 ✕ 108 y
ears. Assuming that this star is essentially at the edge of the galaxy, each of the stars in the galaxy has a mass equal to that of this star, and the stars are distributed uniformly in a sphere about the galactic center, estimate the number of stars in the galaxy. (Do not round your answer to an order of magnitude.)
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