Question

An astronomer measures the velocities of two galaxies, galaxy A and galaxy B. He finds that galaxy A is moving at twice as fast away from us as galaxy B. Assuming these galaxies are moving because of the expansion of space, which statement is true?

a) Galaxy A is closer to us than galaxy B.
b) Galaxy A is further from us than galaxy B.
c) Galaxy A and galaxy B are at the same distance from us.
d) The information provided is not sufficient to make a conclusion.

Answer 1

Galaxy A is further from us than Galaxy B, as supported by Hubble's Law, which correlates galactic velocities to their distances from us.

Step-by-step explanation:

The astronomical observations described relate to galactic recession velocities due to the expansion of the universe. Given that Galaxy A is moving away at twice the velocity of Galaxy B, this would suggest, according to Hubble's Law, that Galaxy A is farther away from us than Galaxy B. This is because Hubble's Law states that the velocity (v) of a galaxy is directly proportional to its distance (d) from us, which is often conceptualized as v = H0d where H0 is the Hubble constant.

Therefore, the correct answer to the student's question is (b) Galaxy A is further from us than Galaxy B. The provided information indicates a relationship between velocity and distance due to the cosmic expansion, allowing for a logical inference on the relative distances of the galaxies in question.