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Milky Way’s Long-Lost Sibling Was Eaten By Andromeda

July 23, 2018
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Milky Way’s Long-Lost Sibling Was Eaten By Andromeda

Scientists at the University of Michigan found that our closest large galactic neighbor has cannibalized Milky Way’s long-lost sibling. 

It turns out the Milky Way galaxy once had a sibling named M32p. A new study has concluded that Andromeda shredded it about 2 billion years ago. Researchers published the study online today (July 23) in the journal Nature Astronomy.

“Astronomers have been studying the Local Group — the Milky Way, Andromeda and their companions — for so long,” study co-author Eric Bell, a professor of astronomy at the University of Michigan (UM), said in a statement. “It was shocking to realize that the Milky Way had a large sibling, and we never knew about it.”

Even though the Milky Way’s sibling was mostly destroyed, it left behind an intriguing trail of evidence. Using computer simulations, Bell and study lead author Richard D’Souza, a postdoctoral researcher at UM, determined that most of the stars in the faint outer reaches of Andromeda’s “halo” — the roughly spherical region surrounding the galaxy’s disk — came from a single smashup.

Researchers can use this method for other galaxies, permitting measurement of their most massive galaxy merger, the researchers say.

“It was a ‘Eureka’ moment,” D’Souza said in the same statement. “We realized we could use this information of Andromeda’s outer stellar halo to infer the properties of the largest of these shredded galaxies.”

M32p was once the third-largest galaxy in our local area.

The new discovery might help researchers further understand how galaxies form and evolve.

“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.”

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Thumbnail image: The Andromeda Galaxy. Credit: Ivan Bok / CC BY 4.0.

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