When Will the Milky Way Collide With Andromeda?
The short answer
Probably in about 6 to 8 billion years, if it happens at all. A 2025 study gave about a 50/50 chance that the two galaxies merge within the next 10 billion years. A 2026 study, using a new measurement of Andromeda's sideways motion, raised that to about 90%. Its authors still call the answer inconclusive.
Andromeda is closing on us at about 110 km/s. Astronomers have known she was heading our way since 1912, but not whether she would hit. In 2012, Hubble measurements pointed to a head on collision in about 4 billion years, and the crash looked certain.
Why the odds keep changing
Her sideways motion across the sky is tiny and hard to measure, and it decides whether she hits us or swings past. Both recent studies name it as the biggest source of doubt.
The 2025 study, by Sawala and colleagues, used Gaia and Hubble data and added the pull of two smaller galaxies. M33 pulls the Milky Way slightly toward Andromeda. The Large Magellanic Cloud pulls the Milky Way off course, away from her. Result: about 50/50 within the next 10 billion years.
The 2026 study, by Wu and colleagues, used a newer measurement of that sideways motion and got 90%. Within the measurement's uncertainty, the odds run from 64.7% to 100%, so the authors call it inconclusive.
A quarter on the Moon
The part of her sideways drift that counts moves her about 13 microarcseconds across our sky each year. A US quarter, 24.26 mm wide, lying on the Moon 384,400 km away, looks 13.0 microarcseconds wide from Earth.
The drift we see from Earth is bigger, about four quarters a year, but most of that is the Sun's own orbit around our galaxy.
If they do merge
Stars are so far apart that almost none would hit each other. The Sun would most likely be flung farther out. Earth has a nearer problem: the warming Sun makes it too hot for life billions of years before any merger.
First, we'll most likely eat a smaller galaxy, the Large Magellanic Cloud. A 2019 study puts that about 2.4 billion years away, and the 2026 study about 1.3 billion. The 2019 study says our central black hole could become up to 8 times as massive. In total mass, Andromeda and the Milky Way are close: about 1.3 and 1.0 trillion Suns.
Key numbers
| What | Number | Source |
|---|---|---|
| Chance of a merger within the next 10 billion years (2025 study) | about 50% | Sawala et al. 2025 |
| Chance of a merger within the next 10 billion years (2026 study) | 90%, with a range of 64.7% to 100% | Wu et al. 2026 |
| Median time to a merger (2026 study) | 6.5 billion years | Wu et al. 2026 |
| Median time to a merger (2025 study) | 7.6 to 8.0 billion years | Sawala et al. 2025 |
| The 2012 prediction | a head on collision in about 4 billion years | NASA 2012 |
| Andromeda's speed toward us | about 110 km/s | van der Marel et al. 2012 |
| The sideways drift that decides it, seen from here | about 13 microarcseconds a year, the size a quarter on the Moon looks from Earth | Our arithmetic from Wu et al. 2026 |
| Total mass | Andromeda about 1.3 trillion Suns, the Milky Way about 1.0 trillion | Sawala et al. 2025 |
| When the Large Magellanic Cloud merges with the Milky Way (2019 study) | about 2.4 billion years | Cautun et al. 2019 |
| When the Large Magellanic Cloud merges with the Milky Way (2026 study, median) | about 1.3 billion years | Wu et al. 2026 |
| Growth of our central black hole from that merger | up to 8 times its mass | Cautun et al. 2019 |
What the film simplifies
- The kisses, the scoreboard, the foam finger and the car drift are cartoon. A miss on the board means no merger in the next 10 billion years, not gone for good: the two galaxies are bound to each other, so the misses loop back.
- Each board of 10 rounds a probability: 10 for 10 stands for the 2012 head on forecast, 5 of 10 for close to 50%, and 9 of 10 for 90%, whose real range runs from 64.7% to 100%.
- "6 to 8 billion years" spans two studies' medians, 6.5 billion (2026) and 7.6 to 8.0 billion (2025), and only applies if they merge.
- "2026. A new study": the study is from 2026, but the measurement of Andromeda's sideways motion it used was published in 2025.
- The quarter on the Moon compares apparent size, and only for the part of the drift that matters. The raw drift seen from Earth is about four quarters a year, mostly from the Sun's own orbit.
- In some shots the Large Magellanic Cloud is drawn bigger next to the Milky Way than it really is, and the gulp is cartoon. The pupil swelling afterwards stands for our black hole, which one study says could become up to 8 times as massive.
At a glance
Runtime 1 minute 6 seconds · Topics: Galaxies, Andromeda, Gravity and orbits, Measuring the sky · Captions on YouTube · Full script below
Test yourself
Andromeda is the same galaxy in 2012, 2025 and 2026. Why did the forecast change twice?
Answer
The data and models changed. The 2025 study added Gaia data and the pull of M33 and the Large Magellanic Cloud, and the 2026 study used a new measurement of Andromeda's sideways motion, which is tiny and hard to measure.
If the two galaxies merge, why would almost no stars crash into each other?
Answer
Stars in each galaxy are so far apart that they almost never meet. The Sun would most likely just be flung farther out.
The 2026 study puts the Large Magellanic Cloud merger about 1.3 billion years from now and the Andromeda merger at a median of 6.5 billion years. About how long is the gap between the two meals?
Answer
About 5 billion years (6.5 minus 1.3 is 5.2).
The script
Andromeda: Pucker up, Milky Way! A trillion star galaxy, incoming!
Milky Way: Pfft. You'll miss. You can't drive straight.
The Cloud (Large Magellanic Cloud): Back off, lady! This cloud's his biggest fan!
Host: 2012. Hubble calls it: head on.
Andromeda: 10 for 10!
Host: 2025. A hit in 10 billion years? About 50/50.
Host: 2026. A new study: more like 9 in 10.
Andromeda: See you in 6 to 8 billion years, big guy!
Host: If.
Milky Way: Make up your minds!
Host: Not yet. It mostly hangs on her sideways drift.
Andromeda: Oh, I drift. Watch this!
Milky Way: Drift a little more, please.
Host: Her drift each year, seen from here?
Host: Like spotting a quarter... on the Moon.
Andromeda: Hard to clock, huh? Then guess where I land!
Milky Way: Pucker up, little buddy.
Host: Before she gets here, we'll most likely eat our biggest fan.
The Cloud (Large Magellanic Cloud): ...Me?
Host: The Large Magellanic Cloud. A whole galaxy.
Andromeda: You're cheating on me with a cloud?!
Milky Way: He fell for me.
The Cloud (Large Magellanic Cloud): ...I made you a foam finger.
Sources
- In 2012, Hubble measurements pointed to a head on collision about four billion years from now. Stars inside each galaxy are so far apart that they will not collide, and the Sun will likely be flung into a new region of the galaxy.NASA 2012
- Andromeda approaches at about 109 km/s, statistically consistent with a head on collision (the 2012 Hubble measurement).van der Marel et al. 2012
- Astronomers knew Andromeda was heading our way as far back as 1912. In 2025, Hubble and Gaia data gave roughly 50/50 odds of a collision within the next 10 billion years. M33 pulls the Milky Way a little toward Andromeda, and the Large Magellanic Cloud pulls it off the orbital plane and away from Andromeda.ESA/Hubble 2025
- Close to 50% chance of no Milky Way and Andromeda merger in the next 10 billion years, using Gaia and Hubble data. M33 and the Large Magellanic Cloud change the orbit. Median merger time 7.6 billion years in the main model; masses about 1.0 (Milky Way) and 1.3 (Andromeda) trillion Suns.Sawala et al. 2025
- A new measurement of the sideways motion (proper motion) of Andromeda and M33 from Gaia DR3 supergiant stars, published in 2025.Wu et al. 2025
- Using that measurement (a sideways speed of 46.7 km/s), the chance of a merger within 10 billion years rises to 90% (64.7% to 100% within the uncertainty), with a median merger time of 6.5 billion years. The Large Magellanic Cloud merges with the Milky Way first, in a median 1.3 billion years. The result remains inconclusive, and Andromeda's sideways motion is the main uncertainty.Wu et al. 2026
- In a merger, the Sun is most likely scattered to the outer halo of the merged galaxy.Cox and Loeb 2008
- The Large Magellanic Cloud will merge with the Milky Way in about 2.4 billion years, and our central black hole could grow in mass by up to a factor of 8.Cautun et al. 2019