Will The Milky Way Collide With Andromeda?
QUICK ANSWER
Yes, the Milky Way and Andromeda are on a collision course. Andromeda is approaching at about 250,000 mph, and the galaxies will start colliding about 4 billion years from now. The merger will take roughly 6 billion years total and produce a single elliptical galaxy informally called Milkomeda.
The Milky Way and Andromeda are headed for a collision. Hubble Space Telescope observations have measured Andromeda's sideways motion across the sky and confirmed the galaxies will collide. The merger will take several billion years and dramatically transform both galaxies into a single elliptical. Recent observations have refined the timing and made the head-on collision slightly less certain than previously thought.
When will the collision happen?
In about 4 billion years. According to NASA, Hubble Space Telescope observations indicate the two galaxies, pulled together by their mutual gravity, will crash together in a head-on collision about 4 billion years from now. Andromeda is currently about 2.5 million light years away and approaching us at roughly 250,000 mph. The initial close approach begins around 3.75 billion years from now, when Andromeda's disk will start filling our night sky. The full merger into a single galaxy will take about 6 billion years total.
What will happen during the merger?
A multi-stage transformation. During the first close approach, gravitational interactions between the galaxies will trigger intense bursts of new star formation, lighting up the sky with new stars and emission nebulae. The galaxies will then pull apart briefly before falling back together for additional close passes. NASA simulations show the two galactic cores eventually merging into a single bright central region. The resulting elliptical galaxy will have lost most of its star-forming gas and will gradually fade.
What happens to Earth and the Sun?
Both will probably survive but end up in a different galaxy. Despite the dramatic-sounding collision, galaxies are mostly empty space. Stars are separated by light years, so direct stellar collisions are extremely unlikely. The Sun and Earth will almost certainly continue intact through the merger, though the Sun's orbit around the galactic center will be dramatically altered. Earth's main concern is unrelated: in about 5 billion years, the Sun will swell into a red giant and likely destroy Earth before the galactic merger completes.
How certain is the head-on collision?
Less certain than once thought. Recent (2024-2025) analyses of Gaia space telescope data have suggested the collision may not be as direct as earlier estimates predicted. Some models now show roughly equal probabilities of a direct collision and a near-miss followed by a slower merger. Either way, the galaxies' gravitational influence will profoundly affect each other, and they will eventually merge. The Triangulum galaxy (M33) may also be drawn into the merger. The eventual elliptical galaxy is informally called Milkomeda.
Yes, the Milky Way and Andromeda will collide. Initial contact begins about 4 billion years from now, with the full merger taking about 6 billion years and producing a single elliptical galaxy informally called Milkomeda. Despite the dramatic collision, individual stars almost never hit each other because galaxies are mostly empty space. Earth probably won't be directly affected, though by then the Sun will have likely already destroyed it as it expands into a red giant.
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