Milky Way-Andromeda Collision May Be Less Likely Than Previously Thought

A new study published in Nature Astronomy suggests that the probability of a future collision between the Milky Way and the Andromeda galaxy may be only 50%—significantly lower than previously believed. The research points to the gravitational influence of the Large Magellanic Cloud (LMC)—the Milky Way's most massive satellite galaxy—as a potential factor in altering the Milky Way's trajectory and possibly averting a direct collision.

For the past century, astronomers have confirmed that Andromeda is moving toward the Milky Way. Based on Hubble Space Telescope data, a 2012 NASA study predicted a direct merger. However, earlier models underestimated the mass of the LMC, recently revealed to be much greater than previously assumed.

Researchers from the University of Wisconsin–Madison and the University of Helsinki used updated data from the Hubble and European Space Agency's Gaia telescopes to simulate the future motions of the Milky Way, Andromeda, the LMC, and Messier 33—the third-largest galaxy in the Local Group—over the next 10 billion years. Across 100,000 simulations, the collision probability between the Milky Way and Andromeda was 50% when considering only the two galaxies; this rose to 66% when including Messier 33, but returned to 50% when the LMC was factored in. The results suggest the LMC's gravitational pull may cause a lateral shift in the Milky Way's motion, helping it avoid a direct hit. However, the study also predicts the Milky Way will eventually absorb the LMC in about 2 billion years.

Some experts remain skeptical, arguing that the total mass of the Milky Way-Andromeda system may still be underestimated, which would imply a higher merger likelihood. A clearer consensus may emerge with more precise dark matter measurements expected in the next decade.