Somewhere in the depths of the night sky, a giant galaxy is hurtling toward us at 110 kilometers per second. Andromeda (M31), the largest galaxy in the Local Group, will collide with our Milky Way in approximately 4.5 billion years. It will be the most spectacular event in our solar system's history.
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🌌 Two Galaxies on a Collision Course
Andromeda lies 2.5 million light-years away — the most distant object visible to the naked eye. It's approaching at ~110 km/s. Updated data from ESA's Gaia satellite shows the collision will occur in ~4.5 billion years (earlier estimates said 4 billion). Research findings indicate the two galaxies have already passed close to each other in the past.
Milky Way
200–400 billion stars
Diameter: ~100,000 light-years
Andromeda (M31)
~1 trillion stars
Diameter: ~220,000 light-years
Collision
~4.5 billion years
Speed: 110 km/s
Milkomeda
The new unified galaxy
Elliptical giant
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💥 What Will Happen
Despite the name “collision,” actual star-to-star collisions are essentially impossible. The distances between stars are enormous relative to their size. What will happen is gravitational disruption on a massive scale: the orbits of billions of stars will be rearranged. The spiral arms will dissolve and spectacular “tidal tails” will form — vast streams of stars and gas extending into space.
⭐ Birth of New Stars
As the vast gas clouds of both galaxies compress, a spectacular wave of new star formation (starburst) will be triggered. Gas compression creates dense regions that collapse under gravity, forming new stars. The sky will light up with millions of new blue stars, making the spectacle dazzling — if anyone is around to see it.
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🕳️ Black Hole Merger
At the center of each galaxy lurks a supermassive black hole. Our Milky Way has Sagittarius A* (~4 million solar masses) and Andromeda has an even larger one (~100–200 million solar masses). After the collision, the two black holes will orbit each other for millions of years, losing energy through gravitational waves, until they finally merge into one.
🌍 Earth's Fate: Good news! Our solar system will most likely survive. The Sun may be pushed to a new orbit — perhaps farther from the new galaxy's center — but Earth and the planets will remain bound to the Sun. Of course, by then the Sun will have become a red giant, making Earth uninhabitable for other reasons.
🔭 "Milkomeda": The New Galaxy
The final result will be a single elliptical galaxy, known as “Milkomeda” or “Milkdromeda.” The spiral arms will have vanished, replaced by a smooth, elliptical shape. NASA simulations show the entire process will take about 2 billion years.
The Triangulum Galaxy (M33), the third largest in the Local Group, may also get caught up in the collision, either absorbed or flung into intergalactic space. Galaxy collisions are common in the universe — Hubble has photographed dozens of examples at various stages. Ours just hasn't happened yet.