The Milky Way and Andromeda are heading toward each other, but whether they’ll actually collide is less certain than scientists once thought. A 2012 analysis of Hubble data suggested a direct impact was almost guaranteed within 5 billion years. Updated measurements using both Hubble and the European Space Agency’s Gaia satellite now put the odds at roughly 50-50 within the next 10 billion years, with only about a 2% chance of a head-on collision in the 4-to-5-billion-year timeframe that was previously treated as a near certainty.
Why the Prediction Changed
Andromeda sits about 2.5 million light-years away and is approaching the Milky Way at roughly 250,000 miles per hour. Measuring that approach speed is straightforward, but predicting the actual collision requires knowing Andromeda’s sideways motion as well. Even tiny differences in that lateral drift, measured over billions of years, can mean the difference between a direct hit and a near miss.
The original 2012 study tracked Andromeda’s motion over a five-to-seven-year window using Hubble observations and concluded the galaxies were on a direct collision course. The newer analysis incorporated additional years of Hubble data plus independent measurements from Gaia, Europe’s star-mapping satellite. Because each variable carries its own margin of error, and those errors compound over billions of years, the team found the outcome is genuinely uncertain. As astronomer Till Sawala put it, there’s an almost equal probability of a dramatic merger or the two galaxies surviving unscathed.
What a Collision Would Actually Look Like
If the galaxies do merge, the process wouldn’t be a single crash. It would unfold over roughly 2 billion years of gravitational interaction, with the galaxies passing through each other, pulling apart, then falling back together. NASA simulations project that by about 6 billion years from now, the two spirals would settle into a single, football-shaped elliptical galaxy, sometimes nicknamed “Milkomeda.”
The merger would also trigger a burst of new star formation. When galaxies collide, their vast clouds of gas and dust slam together and compress, creating dense pockets where new stars ignite at rates far above normal. Gravitational forces would funnel cold gas toward the center of the combined system, potentially lighting up the core with intense stellar activity.
Stars Almost Never Hit Each Other
The word “collision” sounds catastrophic, but galaxy mergers are surprisingly gentle for individual stars and planets. Stars are extraordinarily small compared to the distances between them. The probability of any single star colliding with another during the merger is roughly one in a quadrillion (10 to the negative 15th power). Even in the denser central regions of both galaxies, direct star-on-star impacts are essentially nonexistent. Most of the matter involved, including the invisible dark matter that makes up the bulk of each galaxy’s mass, passes right through without touching anything.
What does change is where stars end up. Gravitational interactions would scatter stars into new orbits. Some of the kinetic energy from the collision gets converted into random stellar motion, reshuffling the positions of billions of stars without destroying them.
What Would Happen to Our Solar System
Earth and the solar system would not be destroyed. NASA simulations show the Sun would likely be flung into a new orbit much farther from the galactic center than its current position, roughly 26,000 light-years out. The night sky would look dramatically different, filled with the brilliant glow of newly forming stars and the distorted spiral arms of two merging galaxies, but our planet would remain gravitationally bound to the Sun just as it is today.
The bigger issue for Earth by that point has nothing to do with Andromeda. In about 5 billion years, the Sun will exhaust its hydrogen fuel and expand into a red giant, making Earth uninhabitable long before any galactic merger would matter for life on this planet.
The Black Holes at the Center
Both the Milky Way and Andromeda harbor supermassive black holes at their cores. The Milky Way’s, called Sagittarius A*, has a mass of about 4 million suns. Andromeda’s is estimated to be significantly larger. In a merger scenario, these two black holes wouldn’t collide immediately. They would first orbit each other in the inner region of the new galaxy, gradually spiraling closer. Simulations estimate they would coalesce within about 17 million years after the galaxies fully merge, a cosmically brief finale to a billion-year process.
That final merger of two supermassive black holes would release an enormous burst of gravitational waves, ripples in the fabric of spacetime. By that point, any observers in the merged galaxy would be far enough from the center that the event would pose no physical danger, though it would be detectable with sufficiently advanced instruments.
The Bottom Line on Timing
The collision is not the foregone conclusion it was presented as a decade ago. The best current data gives it coin-flip odds over the next 10 billion years, with a very small chance of occurring in the previously predicted 4-to-5-billion-year window. If it does happen, the process will take billions of years to complete, individual stars and planets will survive intact, and the end result will be a single large elliptical galaxy. None of this will affect human civilization, which will need to contend with the Sun’s own life cycle long before Andromeda arrives.