The Milky Way looks set to collide with neighbouring galaxy Andromeda – but not for another four billion years.
NASA astronomers predict the Sun will be flung into a new region of the galaxy, but that the Earth and solar system are in no danger of being destroyed.
“Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy,” said Roeland van der Marel of the Space Telescope Science Institute (STScI).
NASA’s Hubble Telescope was used to take measurements of motion of Andromeda and revealed that the galaxy is now unavoidably falling towards the Milky Way under the mutual pull of gravity between the two and the invisible dark matter that surrounds them both. Andromeda is now just 2.5 million light-years away and rushing towards the Milky Way at 250,000 miles per hour.
“After nearly a century of speculation about the future destiny of Andromeda and our Milky Way, we at last have a clear picture of how events will unfold over the coming billions of years,” said Sangmo Tony Sohn of STScI.
Van der Marel’s team conducted extraordinarily precise observations of the sideways motion of Andromeda – also known as M31 – by repeatedly observing select regions of the galaxy over a five-to-seven-year period.
Computer simulations show it will take an additional two billion years after the encounter for the interacting galaxies to completely merge and reshape into a single elliptical galaxy. Stars inside each galaxy are unlikely to collide as they are too far apart, but the stars will be thrown into different orbits around the new galactic centre. Our solar system is likely to be hurled much further from the core than it is today.
Andromeda’s companion, the Triangulum galaxy, will also join in the collision and may merge with the pair. It’s possible it may even hit the Milky Way first.
“In the worst-case-scenario simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits,” said Gurtina Besla. “The stellar populations of both galaxies are jostled, and the Milky Way loses it flattened pancake shape with most of the stars on nearly circular orbits. These galaxies’ cores merge, and the stars settle into randomised orbits to create an elliptical-shaped galaxy.”