Andromeda might have cannibalized our sister galaxy

Scientists believe that Andromeda cannibalized the Milky Way's sister galaxy about 32 million years ago.
By Tyler MacDonald | Jul 24, 2018
Researchers suggest that the Andromeda galaxy, with its satellite galaxies M110 and M32, cannibalized one of our sister galaxies. The result is M32, which is a remnant of the larger galaxy that was eaten approximately 32 billion year ago.

"Astronomers have been studying the Local Groupthe Milky Way, Andromeda and their companionsfor so long," said Eric Bell, a professor of astronomy at the University of Michigan (UM). "It was shocking to realize that the Milky Way had a large sibling, and we never knew about it."

The team used computer simulations to determine that most stars in the outermost edges of Andromeda's "halo" originated from a single location.

"It was a 'Eureka' moment," saidstudy lead author Richard D'Souza. "We realized we could use this information of Andromeda's outer stellar halo to infer the properties of the largest of these shredded galaxies."

Additional modeling revealed the likely date of the merger 2 billion years ago and allowed them to reconstruct some details of the ancient galaxy. The team named it M32p, and believe that it wasat minimum20 times bigger than any galaxy that has ever merged with the Milky Way.

And apparently it's not completely destroyed eitherM32 is likely the galaxy's corpse.

"M32 is a weirdo," Bell said. "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."

The findings were published in Nature Astronomy.

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