Toronto: Andromeda and Triangulum, the two galaxies closest to our own, collided two to three billion years ago, changing the galactic structure, according to evidence unearthed by astronomers.
The collision appears to have plucked millions of stars from the Triangulum disk to form a faint stream visible in the Pan-Andromeda Archaeological Survey (PAndAS) data, says Larry Widrow, professor of physics and Astronomy at Queen`s University.
Andromeda, and our own galaxy the Milky Way, are the two largest members of a small cluster of galaxies known as the Local Group. Triangulum, the third largest member of the Local Group, is about one-tenth the size of Andromeda.
Widrow, along with John Dubinsky of Toronto University, recreated this galactic encounter using a high performance computer and theoretical modelling.
Their simulations illustrate how the strong gravitational field of Andromeda could have pulled stars away from the Triangulum disc creating a stream just as the team saw.
The PAndAS, led by Alan McConnachie of the Herzberg Institute of Astrophysics in Victoria BC, is using the Canada-France-Hawaii telescope to map the Andromeda and Triangulum galaxies.
This map, the largest of its kind, will allow astronomers to test the hypothesis that galaxies grow by "cannibalising" other galaxies, says a university statement.
"We believe that these stars are relics of small galaxies that were destroyed by the powerful tidal fields of a larger galaxy. Our observations also suggest that the Triangulum galaxy is being ripped apart by Andromeda," says Widrow.
"Within a few billion years Triangulum will be completely destroyed by Andromeda and its stars will be dispersed throughout the Andromeda halo.
"And a few billion years after that, Andromeda and the Milky Way will collide and merge together to form a giant elliptical galaxy."
The findings were published this week in Nature.