The 2003 observation of a very distant galaxy, the light from which passed through a less distant galaxy cluster on its way to Earth, 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 Earth's 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 Earth.
C) The apparent blueshift is not unusual. Most distant galaxies look blue because of the predominance 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 correct answer involves the phenomenon of gravitational blueshift, which occurs when light moves towards a massive object, in this case, a galaxy cluster. The observation suggests that the light experienced more blueshift when approaching the cluster than the redshift it experienced moving away, indicating an effect of the cluster's gravity on the light path, rather than a universal contraction or properties related to the age or location of the galaxy. This does not directly suggest a Big Crunch scenario or a difference in mass density between Earth and the distant galaxy's location, nor does it relate to the color of stars in the early universe.

The 2003 Observation of a Very Distant Galaxy, the Light