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In the night sky: Orion
In the night sky: Orion

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3.2.3 Colliding and merging galaxies

Collisions between galaxies take hundreds of millions of years to complete, and are driven by the effect of gravity. Actual collisions between stars are rare, as so much of a galaxy is empty space.

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The Milky Way is itself falling towards the Andromeda galaxy, and in about five billion years, these galaxies will merge. What will this be like? For one thing, the stars themselves won’t collide – they are too sparsely distributed. The galaxies will splash together, flinging some stars out in the process. Eventually the combined system will settle down, perhaps resembling an elliptical galaxy.

The merger won’t affect life on Earth, as our planet will have long since become uninhabitable! As we considered when we were discussing different types of star, in about four billion years from now, the Sun’s luminosity will be too high for liquid water to exist on Earth. At that time, the Andromeda galaxy will appear as large in the sky as either of the Magellanic Clouds do today.

See some images of galaxies colliding that have been taken by the Hubble telescope in the next section.