Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 55 km/s/Mpc
How fast would a galaxy located 500 megaparsecs distant be receding from us? Show all work clearly, and state your final answer with a complete sentence. Give the speed in units of kilometers per second and as a percentage of the speed of light.
v = H0d = (55 (500 Mpc)
= 27,500
= 0.09c
The galaxy is receding from us at 27,500 km/s, or 9 percent of the speed of light.
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