Astronomers have long anticipated a dramatic collision between the Milky Way and its nearest galactic neighbor, the Andromeda galaxy. This cosmic event, often referred to as “Milkomeda,” was predicted to occur in approximately 4.5 billion years. However, a new study published in the journal Nature Astronomy suggests that the likelihood of such a collision is less certain than previously believed.
Despite the Milky Way and Andromeda racing towards each other at a staggering speed of 223,694 miles per hour (100 kilometers per second), the study indicates that the probability of a collision within the next 10 billion years is only about 50%. This is a significant reduction from earlier estimates, which suggested a near-certain collision within 4 to 5 billion years.
Galactic Dynamics and the Role of Smaller Galaxies
The new findings are based on simulations that consider the gravitational influences of other galaxies within the Local Group, a collection of over 100 smaller galaxies that includes the Large Magellanic Cloud (LMC) and the Triangulum galaxy (M33). These simulations utilized data from the Hubble and Gaia space telescopes, running 100,000 scenarios to account for various gravitational interactions.
According to the study, the LMC and M33 exert significant gravitational forces that can alter the trajectories of the Milky Way and Andromeda. “The extra mass of Andromeda’s satellite galaxy M33 pulls the Milky Way a little bit more towards it,” explained Dr. Till Sawala, the study’s lead author from the University of Helsinki. “However, we also show that the LMC pulls the Milky Way off the orbital plane and away from Andromeda.”
Implications of a Potential Galactic Collision
Should a collision occur, it would likely result in the destruction of both galaxies’ spiral structures, forming a new, elongated galaxy. Such mergers are known to create “cosmic fireworks,” with gas feeding a central black hole and emitting vast amounts of radiation. However, the study’s coauthor, Professor Carlos Frenk of Durham University, noted that the new findings offer hope that the Milky Way might avoid this fate.
“Until now we thought this was the fate that awaited our Milky Way galaxy,” Frenk said. “We now know that there is a very good chance that we may avoid that scary destiny.”
Despite this potential reprieve, the study warns of a greater likelihood that the Milky Way could collide with the LMC within 2 billion years, an event that could significantly alter our galaxy’s structure.
Simulating Galactic Futures
The study’s simulations accounted for 22 different variables, including uncertainties in the positions, velocities, and masses of the Local Group galaxies. This comprehensive approach allowed researchers to better understand the range of possible outcomes.
“We ran many thousands of simulations, which allowed us to account for all the observational uncertainties,” Sawala said. “Because there are so many variables that each have their errors, that accumulates to rather large uncertainty about the outcome.”
In over half of these simulations, the Milky Way and Andromeda initially passed closely by each other before eventually merging. In other scenarios, the galaxies crossed paths without significant interaction.
Looking Ahead: The Future of Our Galaxy
While the study provides new insights into the potential future of the Milky Way, it also underscores the uncertainties inherent in predicting cosmic events. Geraint Lewis, a professor of astrophysics at the University of Sydney, emphasized the importance of considering these uncertainties.
“We won’t know if the collision is definitely off in the future, but this clearly shows that the story that people tell — that there will be a collision that will destroy the Milky Way and Andromeda — is not as clear or certain as people think,” Lewis said.
Further data from the Gaia space telescope, expected in 2026, may refine predictions regarding Andromeda’s trajectory and the future of our galaxy. Meanwhile, the fate of the sun, which will become a red giant in about 5 billion years, poses a more immediate concern for Earth.
Ultimately, while the study suggests that the Milky Way-Andromeda collision is less likely than previously thought, the future of our galaxy remains an open question. As Sawala noted, “The end of the sun is far worse for our planet than the collision with Andromeda.”
