For decades, scientists believed the Milky Way was on a cosmic crash course with the Andromeda Galaxy. This collision, projected to occur in about 5 billion years, has shaped the way we imagine the future of our galaxy. But according to a new study published in Nature Astronomy, that apocalyptic fate may not be so certain after all.
50-50 Chance of Collision
A research team led by Till Sawala of the University of Helsinki has recalculated the odds. By factoring in uncertainties from Hubble and Gaia data and considering gravitational influences from neighboring galaxies, they found only a 50% chance the Milky Way and Andromeda will merge in the next 10 billion years.
Why the Collision Was Considered Inevitable
The long-standing prediction of a Milky Way-Andromeda merger stems from measurements of Andromeda’s radial velocity—its motion toward us. This was detected through Doppler shifts in the galaxy’s light. However, transverse velocity—or Andromeda’s sideways drift—was harder to measure and was often assumed to be minimal.
Without accounting for proper motion, earlier studies concluded a direct collision was inevitable.
What This Study Did Differently
Rather than relying on new data, the researchers used existing measurements but emphasized the uncertainties in those values. They simulated thousands of possible galactic trajectories, tweaking initial positions and velocities to capture a broader range of outcomes.
The study also included gravitational effects from two often-overlooked players:
- The Large Magellanic Cloud, a massive satellite of the Milky Way, pulls it slightly away from Andromeda.
- M33 (Triangulum Galaxy) tugs Andromeda slightly toward the Milky Way.
These subtle interactions shift the probability significantly.
Collision or Not—What Does It Mean?
If the galaxies do collide, Earth isn’t necessarily doomed. Stars are so far apart that direct star-on-star collisions are unlikely. The merger would gradually form a larger elliptical galaxy.
But if they don’t collide, the two may become eternal dance partners, orbiting each other without merging—a milder yet equally intriguing outcome.
What’s Still Unknown
The biggest remaining mystery? Andromeda’s transverse velocity. Even tiny differences in this sideways motion can tip the scales between a future merger or a long-term orbital relationship. More precise measurements are expected in coming years.
Until then, humanity’s galactic destiny remains a celestial coin toss—underscoring just how much we’re still learning about our place in the universe.
