I understand how different stars are different colors, and planets, and so-forth. But my thought process assumes the “law of averages” would make most galaxies at least close to the same overall color…..why aren’t they?
In: 42
There’s a few things in play here.
One is general composition. Galaxies can develop a number of different shapes and densities. These conditions can be conducive to developing more larger, blue/white stars, more typical yellow stars, or smaller red stars.
Another is viewing angle. For reasons like those listed above, a galaxy might have a concentration of a certain kind of gas or certain kinds of stars which are more directly visible to us.
Then there’s the weird stuff – red shift and blue shift.
The andromeda galaxy is a galaxy which is moving towards us, and the edge of the galaxy takes on a blue hue because its motion towards us compresses the frequency of the light it emits.
Distant galaxies moving fast away from us appear red because their motion expands the frequency of light as it comes to us.
These are simple explanations of what is a complex phenomenon, but red-shifting galaxies are how we know the universe is expanding.
Redshift and blueshift factor in, too. Galaxies are all in motion. Some galaxies are coming towards us, some away from us, some at incredibly fast speeds. These relative motions compress or elongate the frequencies of the light coming from them, so they get pushed up the spectrum to red or down the spectrum to blue and violet, and everywhere in between.
Since this more or less applies to each given galaxy as a whole, for the most part, it would give lots of galaxies different apparent colors from our perspective on earth.
While all the other comments have very good points, it’s also worth noting [that most images of space & objects in space are colourised](https://www.youtube.com/watch?v=p4Zilqf9Sog)
Literally from the nasa website re the webb images:
Webb’s MIRI image offers a kaleidoscope of colors and highlights where the dust is – a major ingredient for star formation, and ultimately life itself. Blue galaxies contain stars, but very little dust. The red objects in this field are enshrouded in thick layers of dust. Green galaxies are populated with hydrocarbons and other chemical compounds. Researchers will be able to use data like these to understand how galaxies form, grow, and merge with each other, and in some cases why they stop forming stars altogether.
This video touches on the expansion of the universe, time dilation and travelling near speed of light in an engaging way. [A journey to the end of the universe.](https://youtu.be/b_TkFhj9mgk)
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