The 2003 observation of a very distant galaxy,the light from which passed through a less distant galaxy cluster on its way to us,showed an overall blueshift.What is the significance?
A) The observation shows that the most distant galaxies have already started to fall back to the center of the universe (the Big Crunch), and their light experiences a Doppler blueshift.
B) The mass density at our location is larger than the mass density in the vicinity of the very distant galaxy, so light experiences a gravitational blueshift as it moves toward us.
C) The apparent blueshift is not unusual. Most distant galaxies look blue because of the predominence of blue stars in the early universe.
D) The gravitational blueshift experienced by the light approaching the cluster (at an earlier time) outweighed the gravitational redshift it experienced (at a later time) while moving away from the cluster. This suggests an outward cosmological acceleration.

Question

Quizplus · Accepted Answer

The observation of an overall blueshift in the light from a very distant galaxy passing through a less distant galaxy cluster suggests a net gravitational blueshift, despite the fact that the light experienced a gravitational redshift while moving away from the cluster. This can be explained by an outward cosmological acceleration, which would outweigh the gravitational redshift and lead to a net blueshift. Option A is incorrect because it refers to the Big Crunch, which is not currently supported by observational evidence. Option B is incorrect because a larger mass density would result in a gravitational redshift, not a blueshift. Option C is incorrect because the predominance of blue stars in the early universe would result in a broader distribution of blueshifts and redshifts, not a consistent blueshift for a single galaxy.

The 2003 Observation of a Very Distant Galaxy,the Light from Which