Up until 2 billion years ago, the Milky Way had a sister galaxy which almost rivaled it in size. Together with the Andromeda galaxy, our closest galactic neighbor, also known as M31, these three galaxies formed the heavyweights of the Local Group — a dumbbell-shaped region of space about 10 million light-years wide and which huddles together more than 50 galaxies, notes Space.com .
But this giant galaxy, only recently identified as the “long-lost sibling” of the Milky Way, met a gruesome end at the hands of the Andromeda galaxy, “a prolific cannibal” believed to have assimilated hundreds of smaller galaxies during its long existence, reports the media outlet.
The revelation comes from a new study published yesterday in the journal Nature Astronomy and which documents that one of the dwarf galaxies around Andromeda, known as M32, may be the remnant of a violent merger that killed off Milky Way’s sibling — now dubbed M32p.
According to the research conducted by Richard D’Souza and Eric Bell from the University of Michigan (UM) in Ann Arbor, the Andromeda galaxy shredded up and devoured M32p some 2 billion years ago. The remains of this cannibalistic act are now found all over Andromeda’s halo, the large and nearly invisible cloud of young stars surrounding the galaxy, as well as within its peculiar satellite, M32.
“M32 is a weirdo,” Bell said in a statement. “While it looks like a compact example of an old, elliptical galaxy, it actually has lots of young stars. It’s one of the most compact galaxies in the universe. There isn’t another galaxy like it.”
D’Souza and Bell came to their conclusions after an in-depth look at the halo of the Andromeda galaxy. This huge spiral galaxy lies 2.5 million light-years away from our planet in the Andromeda constellation and is thought to have acquired its immense halo by clashing with and absorbing material from countless other galaxies.
But computer simulations performed by the two researchers unveiled that the far reaches of Andromeda’s halo were created after just one giant merger that occurred two billion years ago.
The Andromeda galaxy ate our sister galaxy https://t.co/HEBmN2jjk2
— Engadget (@engadget) July 23, 2018
What is more, the violent encounter with M32p, which tore apart Milky Way’s sibling, left Andromeda’s spiral disk intact — disproving the widely accepted theory that giant mergers destroy these disks turning spiral galaxies into elliptical ones.
“It was a ‘Eureka’ moment,” said D’Souza, the lead author of the study and a postdoctoral researcher at UM. “We realized we could use this information of Andromeda’s outer stellar halo to infer the properties of the largest of these shredded galaxies.”
For instance, by looking at Andromeda’s halo, the duo discovered that Milky Way’s long-lost sibling was the third largest galaxy in the Local Group, after Andromeda and the Milky Way. In addition, the team found out that M32p was at least 20 times larger than any galaxy the Milky Way has ever assimilated.
“Astronomers have been studying the Local Group — the Milky Way, Andromeda and their companions — for so long,” said Bell, who teaches astronomy at the university. “It was shocking to realize that the Milky Way had a large sibling, and we never knew about it.”
As Space.com points out, our Milky Way will experience its own ultimate merger 4 billion years from now, when our galaxy will fuse together with Andromeda in probably the most epic clash the Local Group has ever seen.
