Milky Way-Andromeda Collision (2025): Now Only a Coin Flip

The Milky Way-Andromeda collision is not certain after all. In a June 2025 Nature Astronomy paper, Till Sawala and colleagues found only about a 50% chance that the two galaxies merge within the next 10 billion years, and below 2% within the next 5 billion, overturning a forecast that had become textbook fact.

The question before the paper

Andromeda, our big neighbor, is approaching the Milky Way. In 2012, measurements of its sideways motion with the Hubble Space Telescope led to a famous prediction: a head-on collision in about 4 to 5 billion years, followed by a merger into one giant galaxy. But that forecast depended on precise measurements and on leaving out some players. How certain was it, really?

What the paper found

• A coin flip. There is only about a 50% chance that the Milky Way and Andromeda merge within the next 10 billion years.
• Very unlikely soon. The probability of a collision within the next 5 billion years is below 2%.
• A smaller merger is nearly certain. The Milky Way will almost certainly merge with the Large Magellanic Cloud, its biggest satellite galaxy, within about 2 billion years.

How they did it

The team used updated measurements from the Hubble Space Telescope and ESA’s Gaia mission for the positions, distances and motions of the galaxies. Crucially, they included the gravity of the Large Magellanic Cloud and of M33, the Triangulum galaxy, which tug on the Milky Way and Andromeda. They also took the observational uncertainties into account, exploring the full range of motions allowed by the data rather than a single best guess, and asked how often the galaxies end up merging.

Why it mattered

One of the best-known facts about our galaxy’s future turned out to be a coin flip. The study shows how far-future forecasts depend on precise present-day measurements, and how much Gaia changed them. It also adds a near-term event to the future of the universe timeline: the Milky Way swallowing the Large Magellanic Cloud.

What we know now

As of October 2026, the safe statement is that the Milky Way and Andromeda may merge within about 10 billion years, with roughly even odds. Gaia’s fourth data release, due on December 2, 2026, will sharpen the motions further. Long-range forecasts like Krauss and Scherrer’s end of cosmology, which assumed a single merged galaxy, are affected too. Read more in our Andromeda and Milky Way collision explainer.

Who wrote it

Till Sawala, of the University of Helsinki, led the study, with Jehanne Delhomelle, Alis Deason and colleagues including Carlos Frenk of Durham University’s Institute for Computational Cosmology. Frenk is also a co-author of the NFW dark matter halo profile. It was published in Nature Astronomy on June 2, 2025.

Read the original

Sawala, T., Delhomelle, J., Deason, A. J., et al. (2025). “No certainty of a Milky Way-Andromeda collision.” Nature Astronomy. doi:10.1038/s41550-025-02563-1. Free on arXiv: 2408.00064. Durham University’s press release has a plain-language summary.