Why are gravitationally lensed galaxies blue in color?
I have seen multiple color photographs showing distant yellow galaxies with the clear arcs of more distant galaxies beyond them. (ref. recent book "Einstein's Telescope" by Evalyn Gates). As you might expect, the light arcs from the distant objects form circumferential patterns surrounding the closer galaxies. But what is unusual to my eye is that virtually all of the arcs are blue in color, especially when compared to the closer galaxies that are actually creating the lens. This seems sort of reversed from what I would expect. I would think that the more distant galaxies would favor the red end of the spectrum, while the nearby objects would tend toward the blue, or at least the neutral green portion of the visible spectrum. I understand that it takes a whole lot of red shifting to create visible results, but this appears to be a pattern that, if anything, seems to be contradicting my expectations. Anyone understand this? Is it because the more distant galaxies represent younger stars? If so, why do all lensing galaxies appear to have younger stars than all lensed galaxies?
Forgive my error - I meant to say why do all lensing galaxies show older stars than all lensed galaxies? The obvious answer might be just age based on distance, but there are lots of hot blue stars even in nearby galaxies - 2nd and 3rd generation. What am I missing?
SpaceBoy - i agree. You are making the same point I am. In these photos, the red shifted light from the far distant galaxies appears more blue - noticeably more blue - than the nearby galaxies.
Is it that the galaxies that contain sufficient mass to create the lensing effect generally consist of a higher population of old stars? Maybe that makes sense. They are mostly ellipticals, while the distant ones appear to be ragged spirals.