Why are some galaxies' spectra blueshifted rather than redshifted?
A) Some distant galaxies are gravitationally lensed.
B) Some distant galaxies show the universe was contracting before the Big Bang started.
C) Some nearby galaxies have vigorous star formation and are much bluer than others.
D) Some distant galaxies have AGN at their centers.
E) Some nearby galaxies have small peculiar velocities in our direction.

Question

Quizplus · Accepted Answer

The blueshift observed in some galaxies indicates that they are moving towards us, rather than away from us like the majority of galaxies in the universe, which exhibit a redshift. This suggests that these galaxies have small peculiar velocities in our direction, which can be caused by gravitational interactions with nearby galaxies or clusters.

Why Are Some Galaxies' Spectra Blueshifted Rather Than Redshifted