Remember the Hubble observations from 2012? Scientists looked at Andromeda moving through space and panicked slightly. Their conclusion was stark. Andromeda was coming straight for us. A direct hit. Scheduled for roughly four billion years from now.
Then the data changed.
Later studies suggested maybe we miss entirely. Maybe it takes longer. Maybe nothing happens for another eight billion years. The current consensus, factoring in the gravitational tug of satellite galaxies, sits at exactly 50 percent. A coin toss. Heads we collide, tails we drift by.
You should probably sleep on the couch if that bothers you, mostly because it’s irrelevant. We have eight billion years to worry. If we assume the worst though, and they actually crash, should you pack your bags?
The answer is no. Not really.
Tidal Forces, Not Trucks
Here’s the math. The two galaxies are smashing into each other at roughly one million kilometers per hour. On a highway, that’s instant death. In space? It’s slow. The disks of these galaxies span more than 100 thousand light-years. At that scale, the “crash” unfolds over hundreds of millions of years. The aftershocks linger for billions more.
The masses involved are absurd. Andromeda weighs in at 1.5 trillion solar masses. The Milky Way is lighter, at around 800 billion. Gravity between them is massive, but it’s not simple attraction. It’s differential.
Imagine the two galaxies edge-to-edge. Separated by about 120 thousand light-years. A star on the side facing Andromeda gets yanked hard. A star on the opposite side? It feels much less pull. That difference stretches the galaxy.
They don’t crunch like 18-wheeler trucks. Galaxies are empty space. They’re more like ghosts. They pass right through one another. The gravity pulls them apart into long tendrils of gas, dust, and stars called tidal tails. It looks like taffy being pulled apart in a slow, cosmic dance. Beautiful, really. Then gravity slings them back together. Again and again, until they finally merge.
Stars Miss. Gas Crashes.
Can individual stars hit each other? The odds are terrifyingly low. In our neighborhood, the average star is about a million kilometers across. The gap between us and the next star? Roughly four light-years. That’s 40 trillion kilometers of nothing between them.
Hit that target.
Stars in our area won’t collide. The galactic suburbs are too quiet. Closer to the core, where millions of stars are packed tightly, things get messier. Collisions happen. They create events like V838 Monocerotise—a star system that bloated up and exploded in brightness after swallowing a neighbor. Ugly. Spectacular. Rare for us though.
But gas clouds are different. They sprawl for hundreds of light-years. When the galaxies merge, those clouds crash constantly.
The resulting bursts of star formation would be bright enough to cast shadows on the new planet, should one still exist.
It sparks rapid, violent star birth. The radiation from those newborn giants would be hazardous, yes. But let’s not get ahead of ourselves.
The Real Problem: Black Holes
The scary part isn’t the stars or the gas. It’s what sits at the bottom of the pit.
Both galaxies hold a supermassive black hole. The Milky Way’s Sagittarius A is four million times the mass of our sun. Andromeda’s M31 is heavier still. 140 million solar masses.
During a merger, gas falls inward. It heats up. It forms accretion disks that glow with terrifying high-energy radiation. Both galaxies could turn into active quasars, blasting radiation everywhere. That’s bad for biology.
Then the black holes merge.
When they finally unite, a few billion years into the mess, they emit gravitational waves. These waves would carry as much energy as all the stars in the observable universe combined. Space-time itself would wobble. We don’t know what that does to local orbits, but intuitively, standing nearby sounds unwise.
The silver lining is thin but there.
The Earth won’t be there.
By the time Andromeda arrives, eight billion years out, the Sun will have swelled into a red giant. It will cook the planet, strip the atmosphere, and then collapse into a tiny white dwarf. The show starts after the house has already burned down.
We’re going to miss it entirely. 🌌
