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Q & A: galaxy collisions

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Most recent answer: 12/19/2015
My question concerns the expansion of the universe. If all galaxies we measure are red shifted and moving away from us, it's surely reasonable to assume this is the same for every galaxy? How is it possible then for galaxies to collide?
- Reagen Siedl (age 39)

There's a typical redshift for a given distance from us. Around the typical velocity for galaxies at that distance, there are additional more or less random local velocities.  That part of the velocity, varying between nearby galaxies, can cause collisions.

Mike W.

(published on 12/19/2015)

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