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Why are the Milky Way and Andromeda Galaxies Moving Toward Each Other While the Universe is Expanding?

-- joel | April 21, 2021

Question:

if everything is moving away from everything else, how we can they say the milky way and andromeda will someday colide?

-- joel

Answer:

The Andromeda and Milky Way galaxies are moving toward each other due to mutual gravitational attraction. This mutual gravity force is stronger than the force which causes the expansion of the Universe on the relatively short distances between Andromeda and the Milky Way. This interaction between the Andromeda and Milky Way galaxies is actually quite common in the Universe, where we see many galaxies either in the process of interaction, or even collision, or showing evidence of past interaction. These more “local” interactions exist over relatively small size scales, in comparison to the size scales over which the expansion of the Universe is measured.

-- Jeff Mangum

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