The Andromeda Collision: When Two Galaxies Meet and What Happens to Everything We Know

Right now, a galaxy of a trillion stars is falling toward us.

Andromeda — the faint smudge visible on clear autumn nights — is approaching the Milky Way at 110 kilometres per second. For decades, astronomers called the collision inevitable: a first close encounter in roughly four billion years, a final merger billions of years after that, producing a new galaxy astronomers have already named Milkomeda.

Then, in early 2025, a paper published in Nature Astronomy changed everything. When scientists properly included the gravitational influence of the Large Magellanic Cloud on the Milky Way's trajectory, the probability of a direct merger dropped to approximately 50 percent. A coin flip. The collision that textbooks treated as certain may not happen at all.

The Andromeda Collision tells the full story — what we know, what we've just discovered we don't know, and what will unfold either way.

Drawing on the latest science including Gaia proper motion measurements, JWST observations of Andromeda's structure, and the 2025 Nature Astronomy findings, Marcus Veylan takes readers through the physics of galaxy collision from first principles: how dark matter halos drive the encounter, why colliding galaxies produce new stars instead of destroying them, what happens to the solar system, how the night sky will transform over billions of years, and what becomes of the two supermassive black holes — one 25 times more massive than our own — at the hearts of both galaxies.

What you will find in this book:

- The 2025 discovery that overturned a century of collision certainty
- Why the stars won't collide even when the galaxies do
- What the night sky will look like four billion years from now
- The fate of Earth, the solar system, and the Milky Way's stars
- The merger of two supermassive black holes and the gravitational waves it will produce
- Milkomeda — the new galaxy that may emerge

A landmark event in the history of our corner of the cosmos. Whether it happens or not, the science is extraordinary.