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| Space on Jul 23, 2014

Will the Andromeda galaxy someday collide with our Milky Way?

The Andromeda galaxy is approaching our Milky Way galaxy across the vastness of space. When will they collide?

Will the Milky Way and Andromeda galaxies collide someday?

According to astronomers: Yes.

For decades, astronomers have been saying that our home galaxy, the Milky Way, is destined someday to collide with the next-nearest spiral galaxy, in the direction of the constellation Andromeda. When they collide, our sun will likely be flung into a new region of galactic space.

But when is that someday?

Is there a more precise number for that someday? Scientists say it will happen four billion years from now. NASA astronomers say they can now predict the time of this collision of titan galaxies with certainty. They base this number on painstaking NASA Hubble Space Telescope measurements of the motion of the Andromeda galaxy, which is also called M31. The scientists said:

The galaxy is now 2.5 million light-years away, but it is inexorably falling toward the Milky Way under the mutual pull of gravity between the two galaxies and the invisible dark matter that surrounds them both.

Here’s a video showing how it might look: Night sky as Milky Way and Andromeda galaxies merge

This image represents Earth's night sky in 3.75 billion years. The Andromeda galaxy (left) will fill our field of view then, astronomers say, as it heads toward a collision with our Milky way galaxy. Image Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

When it happens, these astronomers say, our Milky Way will get a “major makeover.” For example, according to these scientists:

It is likely the sun will be flung into a new region of our galaxy, but our Earth and solar system are in no danger of being destroyed.

Yup. Good to know. And by the way our sun – which is a middle-aged star – is about four-and-a-half billion years old.

Bottom line: According to astronomers, our Milky Way galaxy and the Andromeda galaxy will collide in four billion years.