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Collision Course

Celestial Tour: Collision Course—The Milky Way and Andromeda

Most galaxies are moving away from our Milky Way Galaxy, but the nearby Andromeda Galaxy is hurtling toward us.

Colliding Galaxies
Produced by the Space Telescope Science Institute’s Office of Public Outreach.
All images, illustrations, and videos courtesy of NASA, ESA, and STScI except:
  • Taurus constellation drawing from Firmamentum Sobiescianum sive Uranographia by Johannes Hevelius, courtesy of the United States Naval Observatory
  • Large galaxy collision animation courtesy of NASA/Goddard Space Flight Center and the Advanced Visualization Laboratory at the National Center for Supercomputing Applications, B. Robertson, L. Hernquist
  •  Expanding universe animation courtesy of NASA
  • Andromeda Galaxy image courtesy of Digitized Sky Survey 2, acknowledgment: Davide De Martin (ESA/Hubble)
  • Animated pan through Milky Way courtesy of ESO/M. Kornmesser
  • Animation of stars moving courtesy of Frank Summers (STScI)
  • Animation of random stellar orbits courtesy of NCSA, UCLA/Keck
  • Milky Way formation animation ©Prof. Romain Teyssier (University of Zurich)
  • Major and minor galaxy merger animations ©Dr. Benjamin Moster (Max-Planck-Institute for Astrophysics)
  • Fly-around animation of Sagittarius Dwarf Galaxy courtesy of David Law (Dunlap Institute, University of Toronto)
  • Animation of two colliding spiral galaxies courtesy of Volker Springel, Max-Planck-Institute for Astrophysics
  • Written by Vanessa Thomas and John Stoke
  • Designed by John Godfrey and Marc Lussier
  • Music courtesy of Association Production Music


 Two swirling glowing objects collide on a black background. Text appears, Collision course. As the universe expands, most galaxies are moving away from our Milky Way galaxy. Moving through a black field dotted with glowing galaxies. 

A spiral shaped galaxy tilted at an angle, diffused clouds surrounding a central bright point in space. Text, The nearby Andromeda galaxy however is hurtling toward us at over 100 kilometers per second or 250,000 miles per hour. Will it hit us some day? 

Until recently, astronomers weren't sure. 

Animations of two spinning disc-shaped galaxies moving towards each other, the larger Milky way and smaller Andromeda. Text, They hadn't been able to measure Andromeda's sideways motion, only its motion directly toward us. So no one knew whether our run-in with Andromeda would be a direct hit, a side swipe, or a total miss. 

An animation of a cylindrical satellite flying above earth's atmosphere. Text, the sharp-eyed resolution of the hubble space telescope has now revealed our galaxy's fate. Hubble imaged star fields in the Andromeda galaxy several years apart. Zooming in on a minuscule chunk of night sky filled with stars glowing red, blue, white, and yellow. Text, By measuring how much the stars shifted in the sky during that time, astronomers calculated Andromeda's sideways drift and projected it into the future. Years count up from 2002 to 32,002. Text, their conclusion? The milky way and andromeda are destined for collision in about 4 billion years. 

An animation of the galaxies colliding and spiralling apart in loose waves and particles. 

An image of looking up at the milky way in the night sky, densely clustered white stars in a dark stripe of cloud-like formations. Text, Over the next few billion years the andromeda galaxy will grow bigger in our sky. 2 billion years and 3.75 billion years from today, an image of the spiral shaped andromeda galaxy growing larger next to the milky way in the sky. Text, Eventually it will rival the band of the milky way for night sky prominence. 3.85 billion years from today, Andromeda's dark clouds and bright red and yellow stars fill the sky. Text, As the galaxies crash together, their spiral disks will twist. Gas from the two galaxies will collide igniting a firestorm of new star birth. 3.9 billion years from today, the sky overwhelmed with clusters of red and yellow stars in dark galaxy clouds. 4 billion years from today, bright patches of galaxy in the sky twisting around each other. Text, After the galaxies swing past each other, andromeda will look stretched out and our milky way warped. 

Later, gravity will pull the galaxies together again. 5.1 billion years from today, a night sky filled with pale light and dotted with stars. Text, by then no evidence will remain of the two great spiral structures. They'll appear simply as big bright blotches in the sky. 

Finally, the two galaxies will merge into one large elliptical galaxy. 7 billion years from today, the sky glowing with pale white light and filled with stars. Text, The new galaxy's brilliant core will dominate the night skies of any planets in the galaxy. 

A dark orange cloud moving in space. Text, despite the head on collision, the sun and most of the stars from the two galaxies are expected to survive. The stars are so far apart that they will simply sip past each other during the galactic merger. However, gravitational forces will throw the stars out of their orbits and toss them around the accident site. An animation of snarling paths of stars. 

Text, After the merger is complete, our sun and solar system will likely loop in and out of the new galaxy's center for the rest of eternity, or at least until the next galactic collision. An animation of the sun forming loops around the bright galaxy center.