How do galaxies evolve? When did they start forming? Those are questions astronomers and cosmologists are working to answer. The standard path includes early bright starforming activity, a middle age, and then a quiescent old age where they stop making stars. That changes if the galaxy happens to collide with another one, because that spurs new bouts of starbirth. It's been this way since stars and galaxies first began forming, slightly less than a billion years after the Big Bang.
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