Our Milky Way Might Not Crash Into the Andromeda Galaxy After All—New Simulations Suggest a 50-50 Chance of Merging
Scientists previously predicted the pair of galaxies would merge in about five billion years. Now, research suggests that outcome is less certain than thought
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Astronomers have long thought the Milky Way was destined to merge with the nearby Andromeda galaxy. The aftermath of this predicted clash has been dubbed “Milkomeda,” and researchers predicted it would happen in four or five billion years.
Now, it turns out our home galaxy may escape this fate: These two celestial giants have a 50 percent chance of avoiding a collision in the next ten billion years, according to a new study published Monday in Nature Astronomy.
“We now find that the earlier prediction of a Milky Way-Andromeda collision is only one of several possibilities,” lead author Till Sawala, an astrophysicist at the University of Helsinki in Finland, tells Science Alert’s Michelle Starr. “Of course, the fate of the Local Group [of galaxies] is not chaotic—with even better data, there will be a definite answer to the question of whether the Milky Way and Andromeda will merge or not, so our study certainly won’t be the final word on this issue.”
Galactic collisions are nothing new. Galaxies in space often merge, infusing areas with hot gas and dust needed to fuel new star formation. But while the intense gravity in a merger would rip some stars apart and throw many solar systems into disarray, most stars would be unscathed due to the vast distances between them, writes National Geographic’s Robin George Andrews. They would just recombine into a different, massive galaxy.
If the Milky Way and Andromeda galaxies did collide, the merger would be strong enough to throw the sun into a new region in space, wrote NASA in 2012, when astronomers predicted this crash was a near-certainty.
Drawing upon observations by the Gaia and Hubble space telescopes, the team ran thousands of simulations of different scenarios over the next ten billion years. This time, they accounted for other celestial objects, factoring in updated estimates on the masses of nearby galaxies that could influence the odds of a merger between the Milky Way and Andromeda.
“A head-on collision is very unlikely; we found a less than 2 percent chance for that. In most of the cases that lead to a merger, the two galaxies will indeed fly past each other at first, which will lead to a loss of orbital energy and subsequently to a merger,” Sawala tells Space.com’s Robert Lea. “How close they come on their first passage is very uncertain, however, and if they don’t come very close, meaning if their distance is more than around 500,000 light-years, they might not merge at all.”
Exactly which of these scenarios ultimately occurs could be governed by the masses of the Large Magellanic Cloud (LMC) and the Triangulum galaxy, two galactic players in the Local Group. In the team’s simulations, the spiral-shaped Triangulum galaxy’s gravity increased the chance of a collision between the Milky Way and Andromeda, while the LMC decreased the chance of a clash, reports Marica Dunn for the Associated Press.
In the simulation where all four objects—the LMC, Triangulum, the Milky Way and Andromeda—were included, the odds of an eventual merger were predicted at 50 percent.
Dark matter and dark energy might also influence how these galactic giants interact, but those effects aren’t well understood, per National Geographic. Essentially, astronomers need more observations to say for sure what will ensue in the stars billions of years from now.
The new study is giving researchers another look at what could happen in the future. But for the time being, “the fate of our galaxy is still completely open,” the study authors write.
“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,” Sawala tells Science Alert.
