Spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A.According to Hubble's law,what can you say about their approximate relative distances?
A)Galaxy A is twice as far as Galaxy B.
B)Galaxy B is four times as far as Galaxy A.
C)Galaxy A is four times as far as Galaxy B.
D)Galaxy B is twice as far as Galaxy A.
E)Not enough information to say-you need to know Hubble's constant to answer this question.

Question

Quizplus · Accepted Answer

Hubble's law states that the recessional velocity of a galaxy is proportional to its distance from us. Since the spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A, we can infer that Galaxy B is moving away from us faster than Galaxy A. Therefore, according to Hubble's law, Galaxy B is also farther away from us than Galaxy A. The redshift factor is proportional to the relative velocity and therefore, the redshift factor of Galaxy B is double that of Galaxy A, which implies that Galaxy B is twice as far away from us as Galaxy A. Hence, the correct answer is D.

Spectral Lines from Galaxy B Are Redshifted from Their Rest