The Milky Way Might Not Crash Into the Andromeda Galaxy After All

New simulations suggest that the long-assumed collision between the Milky Way and Andromeda galaxies is not guaranteed, with the odds now estimated at just over 50% within the next 10 billion years. Factoring in other massive galaxies like M33 and the Large Magellanic Cloud revealed that their gravitational influence significantly alters the likelihood of a merger. ScienceAlert reports: The Milky Way and Andromeda are not, however, alone in this little corner of the cosmos. They belong to a small group of galaxies within a radius of about 5 million light-years from the Milky Way known as the Local Group. The Milky Way and Andromeda are the largest members, but there are quite a few other objects hanging out that need to be taken into consideration when modeling the future. [Astrophysicist Till Sawala of the University of Helsinki] and his colleagues took the latest data from the Hubble and Gaia space telescopes, and the most recent mass estimates for the four most massive objects in the Local Group -- the Milky Way, Andromeda, the Triangulum galaxy (M33), and the Large Magellanic Cloud (LMC). Then, they set about running simulations of the next 10 billion years, adding and removing galaxies to see how that changed the results.

Their results showed that the presence of M33 and LMC dramatically altered the probability of a collision between the Milky Way and Andromeda. When it is just the two large spiral galaxies, the merger occurred in slightly less than half the simulation runs. The addition of M33 increased the merger probability to two in three. Taking M33 back out and adding LMC had the opposite effect, decreasing the probability to one in three. When all four galaxies were present, the probability of a merger between the Milky Way and Andromeda within 10 billion years is slightly more than 50 percent. 'We find that there are basically two types of outcomes,' Sawala said. 'The Milky Way and Andromeda will either come close enough on their first encounter (first 'pericenter') that dynamical friction between the two dark matter haloes will drag the orbit to an eventual merger, which very likely happens before 10 billion years, or they do not come close enough, in which case dynamical friction is not effective, and they can still orbit for a very long time thereafter.'

'The main result of our work is that there is still significant uncertainty about the future evolution -- and eventual fate -- of our galaxy,' Sawala added. 'Of course, as a working astrophysicist, the best results are those that motivate future studies, and I think our paper provides motivation both for more comprehensive models and for more precise observations.'

The research has been published in Nature Astronomy.

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