Astronomers long expected the Milky Way and Andromeda to collide in about 4.5 billion years — but a 2025 study in Nature Astronomy, using Hubble and Gaia data, estimated only a roughly 50–50 chance of the galaxies merging within the next 10 billion years.

The 2025 estimate depended on uncertain motions and neighbouring galaxies. A 2026 follow-up put the merger probability higher, showing why the forecast remains sensitive to the measurements. The post Astronomers long expected the Milky Way and Andromeda to co…