Andromeda galaxy will deliver a ‘glancing blow’ to our Milky Way

Astronomers have long suspected that the colossal Andromeda galaxy would, in billions years, collide with our humble Milky Way.

The collision was forecast to happen in some 3.9 billion years. But after astronomers analyzed new data captured by the European Space Agency’s star-surveying satellite Gaia, they now put the imminent date at 4.5 billion years — so 600 million years later than initially expected.

The event, detailed in The Astrophysical Journal, is characterized as a “swipe” rather than a direct collision. The end result would be a merger of the galaxies into one, monstrous galaxy. 

“This finding is crucial to our understanding of how galaxies evolve and interact,”  Timo Prusti, ESA Gaia Project Scientist who had no role in the study, said in a statement. 

The Gaia satellite measured star motion in the Andromeda galaxy.

While of immense importance to our corner of the universe, this event will be of little importance to Earth: By then, our aging sun will have grown brighter and likely have boiled the oceans while burning away our protective atmosphere. 

To arrive at their conclusions about the future galactic meeting, scientists observed how stars moved within two “nearby”  galaxies that are passing each other —  the Andromeda and Triangulum galaxies  — to forecast how Andromeda will ultimately travel through intergalactic space.

 “We combed through the Gaia data to identify thousands of individual stars in both galaxies, and studied how these stars moved within their galactic homes,” said study coauthor Mark Fardal in a statement. “While Gaia primarily aims to study the Milky Way, it’s powerful enough to spot especially massive and bright stars within nearby star-forming regions – even in galaxies beyond our own.”

Galactic trajectories.

When Andromeda does eventually meet, or “swipe,” the Milky Way, it doesn’t mean chaos and destruction will ensue.

“That event will be less dramatic than it sounds, however,” noted The New Times cosmos reporter Dennis Overbye. “Because galaxies are mostly empty space, they will pass through each other like ghosts.”