Milky Way set to strike neighbor galaxy
The Milky Way is set for a head-on collision with its closest neighbor, the Andromeda galaxy, astronomers predicted this week. Galactic residents need not brace for impact just yet, however: The mash-up won’t take place for another 4 billion years.
Andromeda, officially known as Messier 31, or M31, is located about 2.5 million light-years from our Milky Way. But that gap is slowly narrowing, a fact that has prompted scientists to wonder whether the two spiral galaxies are destined to merge.
“To know if this will in fact happen, it’s necessary to know not only how Andromeda is moving in our direction, but also what its sideways motion is,” Roeland van der Marel, an astronomer at the Space Telescope Science Institute in Baltimore, said Thursday. “That will determine whether Andromeda will miss us at a distance — or whether it might be heading straight for us.”
The galaxy’s gradual sideways movement is extremely hard to measure because, on our short time scale, Andromeda doesn’t seem to budge. Over a few billion years, though, such minimal movement would make a big difference.
So scientists enlisted the Hubble Space Telescope to measure the tiny sideways shifts in the galaxy’s stars over a 5- to 7-year period. They used those movements to plot Andromeda’s mostlikely path — and it brought M31 straight into the Milky Way’s spiral arms.
Over about 2 billion years, the galaxies would merge, forming a more globular, nonrotating agglomeration known as an elliptical galaxy. The sun would probably be flung farther from the Milky Way’s center, but Earth would probably not be disturbed: The scientists said it’s unlikely that any star would come close enough to our solar system for its gravity to disrupt our planet’s position around the sun.
Andromeda is now headed toward us at a relative speed of 250,000 mph — a pace that would allow it to reach the moon from the Earth in an hour. As gravity pulls the two galaxies inexorably closer, it will accelerate up to five times the current speed, scientists said.
Andromeda’s smaller companion galaxy, M33, could join the collision for an intergalactic group hug.
The astronomical analysis will be published in the Astrophysical Journal.