For years, astronomers have predicted a dramatic fate for our galaxy: a head-on collision with Andromeda, our nearest large galactic neighbour. This merger – expected in about 5 billion years – has become a staple of astronomy documentaries, textbooks and popular science writing.

But in our new study published in Nature Astronomy, led by Till Sawala from the University of Helsinki, we find the Milky Way’s future might not be as certain previously assumed.

By carefully accounting for uncertainties in existing measurements, and including the gravitational influence of other nearby galaxies, we found there is only about a 50% chance the Milky Way and Andromeda will merge in the next 10 billion years.

The idea that the Milky Way and Andromeda are on a collision course goes back more than a century. Astronomers discovered Andromeda is moving toward us by measuring its radial........

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