The Sagittarius galaxy is about 50,000 light-years from the Milky Way’s core, and contains a large amount of dark matter, which researchers believe is the driving force behind the collisions.
The force of the two cosmic bodies impacting sent out stellar streams in both, which were pulled outward into ringed arms by the Milky Way’s rotation.
“It’s kind of like putting a fist into a bathtub of water as opposed to your little finger,” said cosmologist James Bullock at the University of California, Irvine in a press release.
As our galaxy is larger, its greater gravitational forces have drawn large amounts of stars and dark matter from Sagittarius into the Milky Way’s arms.
“When all that dark matter first smacked into the Milky Way, 80 percent to 90 percent of it was stripped off,” said lead author Chris Purcell at the University of Pittsburgh in the release.
“That first impact triggered instabilities that were amplified, and quickly formed spiral arms and associated ring-like structures in the outskirts of our galaxy.”
The third clash is due to take place on the southern side of the Milky Way’s disk in about 10 million years, according to Purcell.
