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Are There Galaxies That Are Moving Toward Each Other?

-- Chase | September 10, 2020

Question:

I know the red shifting of light as galaxy’s move away is used to measure the distance between galaxies and is used as evidence for the accelerating expansion of the universe. I’m curious has the same investigation ever been done between blue shifted galaxies or galaxies that are approaching each other to see if they are accelerating towards each other and see if they are moving towards each other slower, faster, or as expected from gravitational attraction alone? Just been looking for data on this, but all I see people talking about is redshifted galaxies.

-- Chase

Answer:

On large scales, beyond the distances over which galaxies can interact via their mutual gravitational force, galaxies all tend to be moving away from each other, following the overall expansion of the universe. When one looks over smaller distances, though, galaxies can mutually attract each other due to gravity, thus are in fact moving toward each other. Our Milky Way and the nearby Andromeda Galaxy are two examples of such a pair of galaxies that are moving toward each other due to gravity.

-- Jeff Mangum

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