Study concludes feared Milky Way-Andromeda collision may never happen

UPI

02-06-2025

A new study found that there was only a 2% probability of the Milky Way and Andromeda galaxies colliding. Photo by NASA ESA Z. Levay and R. van der Marel, STScI T. Hallas and A. Mellinger
May 30 (UPI) -- A new European study out Monday throws into question conventional wisdom that the Milky Way and Andromeda galaxies are on a collision course that will take out our galaxy and the solar system with it.
Published in the journal Nature Astronomy, the research by scientists at the universities of Helsinki, Durham and Toulouse concluded that while the two galaxies are hurtling toward each other at more than 223,600 mph there was only a 2% probability of them colliding in the next 5 billion years.
The finding from running 100,000 simulations based on the latest observational data, including the impact from the Milky Way's Large Magellanic Cloud and controlling for potential misreads, contradicts the previously held belief that the Milky Way has 5 billion years maximum left, Durham University said in a news release.
The Milky Way and Andromeda experience at least one close encounter, passing each other by at a distance of 500,00 light years, in a little more than half of the simulations, before they lose so much orbital momentum that they collide.
But that is not predicted to happen for another 8-10 billion years, long past the time by which our sun will have died anyway.
In most other scenarios run in the study, the distances at which the Milky Way and Andromeda pass are so vast that they continue their onward evolution into the mists of time undisturbed.
However, the findings do not mean the calculations by which the previously held conclusions were arrived at were wrong, stressed lead author Till Sawala, but rather that more recent data was available to the team.
The new data gathered by NASA's Hubble and the European Space Agency's Gaia space telescopes enabled the scientists to include more variables in their simulations.
"When we tried to start from the same assumptions as previous researchers, we recovered the same results. We've simply been able to explore a much larger space of possibilities, taking advantage of new data," said Sawala, a researcher in Helsinki University's Theoretical Extragalactic Astrophysics Group.
"While some earlier works had focused on the interaction between the Milky Way, Andromeda, and the Triangulum galaxy, we also include the effect of the LMC.
"Although its mass is only around 15% of the Milky Way's, its gravitational pull directed perpendicular to the orbit with Andromeda perturbs the Milky Way's motion enough to significantly reduce the chance of a merger with the Andromeda galaxy," Sawala said.
"And while earlier studies only considered the most likely value for each variable, we ran many thousands of simulations, which allowed us to account for all the observational uncertainties."
Professor Alis Deason of Durham University's Institute for Computational Cosmology said the findings had significance "for the fate of our Galaxy," because there was a chance that the predestined merger with Andromeda, creating a gargantuan so-called "Milkomeda," might never come to pass.
The team is preparing to extend their research when more fresh data becomes available, running further scenarios that will enable them to map out the galaxies' futures.
Precise measurements of some of the most critical but notoriously difficult to measure variables are expected any day from Gaia, including the transverse motion of Andromeda.
Durham's Professor Carlos Frenk, the lead cosmologist on the project, said the universe "is a dynamic place, constantly evolving."
"We see external galaxies often colliding and merging with other galaxies, sometimes producing the equivalent of cosmic fireworks when gas, driven to the centre of the merger remnant, feeds a central black hole emitting an enormous amount of radiation, before irrevocably falling into the hole," said Frenl.
"Until now we thought this was the fate that awaited our Milky Way galaxy. We now know that there is a very good chance that we may avoid that scary destiny."
Frenk said the capacity to precisely simulate how vast galaxies made up of hundreds of billions of stars will evolve across billions of years showed what could be achieved in the field.
"This is a testimony to the power of physics allied to the power of large supercomputers," he said.