It’s been textbook knowledge for over a century that our Milky Way galaxy is doomed to collide with another large spiral galaxy, Andromeda, in the next 5 billion years and merge into one even bigger galaxy.
Both the Milky Way and the Andromeda galaxies (M31) are part of what’s known as the Local Group (LG), which also hosts other smaller galaxies (some not yet discovered) as well as dark matter (per the prevailing standard cosmological model).
“The Milky Way and Andromeda alone would remain in the same plane as they orbit each other, but this doesn’t mean they need to crash.
“The extra mass of Andromeda’s satellite galaxy M33 pulls the Milky Way a little bit more towards it.
However, we also show that the LMC pulls the Milky Way off the orbital plane and away from Andromeda.
Our Milky Way galaxy is destined to collide with Andromeda, another massive spiral galaxy, within the next five billion years, forming an even larger galaxy. This has been textbook knowledge for more than a century. However, a recent study that was published in the journal Nature Astronomy is giving that established narrative a more ambiguous appearance. Given that there is a roughly 50% chance that the two galaxies will avoid a collision and merger within the next 10 billion years, the authors conclude that the likelihood of this happening is more akin to the odds of a coin flip.
The Milky Way and Andromeda galaxies (M31) are both members of the Local Group (LG), which is also home to dark matter (according to the dominant standard cosmological model) and other smaller galaxies, some of which have not yet been found. The authors claim that remnants of previous mergers and interactions with other galaxies are already present in both.
“Predicting future mergers requires knowledge about the present coordinates, velocities, and masses of the systems partaking in the interaction,” the authors stated. This includes both dynamical friction and the gravitational pull between them. Since it results in the decay of galactic orbits, the latter is more prevalent when galaxies are on the verge of merging.
In this most recent analysis, data from the European Space Agency’s (ESA) Gaia space telescope and the Hubble Space Telescope were combined to run 100,000 Monte Carlo computer simulations, accounting for the entire LG system in addition to the Milky Way and Andromeda. The results of those simulations produced a completely different conclusion: the likelihood of galaxies colliding within the next 10 billion years is roughly 50/50. Within the next 4 to 5 billion years, there is still a 2% chance that they will collide. According to the authors’ conclusion, “the fate of our galaxy is still completely open based on the best available data.”.
Two additional LG galaxies—the Large Magellanic Cloud (LMC) and the satellite galaxy M33—provide one confounding factor. The simulations showed that the former raises the chance of a collision, but the LMC’s orbit is perpendicular to the orbit of the Milky Way and Andromeda, so this is offset.
Even though the Milky Way and Andromeda would continue to orbit one another in the same plane, they wouldn’t have to collide. According to co-author Till Sawala of the University of Helsinki in Finland, “they could still pass each other.”. “Andromeda’s satellite galaxy M33’s excess mass draws the Milky Way slightly closer to it. The Milky Way is pulled away from Andromeda and off the orbital plane by the LMC, as we also demonstrate. Although it lessens the likelihood, the LMC does not guarantee that we will avoid that merger. “”.
Has the time come to revise the textbooks? Not yet. Further data and analysis are required to validate these recent findings. “It is a little ironic that we are now less certain about the outcome of a potential collision, even with the addition of more precise Hubble data taken in recent years,” Sawala said. The more intricate analysis and the fact that we view it as a more comprehensive system are the reasons for this. However, it will take even better data to arrive at a new prediction regarding the Milky Way’s ultimate destiny. “”.
2025; DOI: Nature Astronomy. 10.1038/s41550-025-02563-1 (Related to DOIs).
