Published: Thu, July 26, 2018
Sci-tech | By Patricia Wade

Scientists 'Shocked' To Discover Milky Way's Long-Lost Sibling

Scientists 'Shocked' To Discover Milky Way's Long-Lost Sibling

Scientists have discovered the remnants of a galaxy hiding in plain sight. It's one of the most compact galaxies in the universe. Because of a voracious appetite, a galaxy like Andromeda is expected to have consumed hundreds of smaller galaxies and the nearly invisible large halo of stars surrounding it contains the remnants of those cannibalized galaxies.

The galaxy was ripped to shreds by Andromeda, our nearest galactic neighbor, the new paper claims.

Astronomers said that - billions of years ago - the disrupted galaxy, M32p, was the third-largest member of our Local Group of galaxies. Today we can discern only traces of weak, sparse galactic "halo" of stars around the Andromeda galaxy, dwarf elliptical galaxy M32 not far from it.

It would only have been smaller than Andromeda and the Milky Way themselves, making it among the largest galaxies in the Local Group. However, using computer models now, scientists have found that much of that external halo is in fact made of one huge galaxy that was harshly shredded by Andromeda.

"It was a "eureka" moment". Scientists already knew that Andromeda was a savage galaxy responsible for the destruction of hundreds of other galaxies, but by using new computer simulations, the U of M team (Richard D'Souza and Eric Bell) were able to determine that most of stars in the halo around the cannibal are from one large galaxy. The galaxy, labeled M32 in its current form by astronomers, now hangs out in the outskirts of the larger Andromeda galaxy, but it's just a shadow of what researchers believe it used to be.

"It was a "eureka" moment", says University of MI astronomer Richard D'Souza, lead author of the paper in Nature Astronomy.

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In this photo of the Andromeda galaxy, the small satellite galaxy M32 is to the left of center.

And earlier this year, a study suggested that the Andromeda galaxy's disk - comprised of stars, gas and dust - had thickened and the galaxy experienced a surge of star formation two billion years ago.

Due to the results of the study, scientists may alter the traditional understanding of how galaxies evolve and whether large interactions would destroy disks and form an elliptical galaxy.

"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.

Researchers said it was likely to be at least 20 times bigger than any galaxy the Milky Way has ever merged with.

"The Andromeda Galaxy, with a spectacular burst of star formation, would have looked so different 2 billion years ago", said Bell. And also a separate compact galaxy M32. Andromeda is close enough so its halo can be studied and the researchers can discover its dramatic mergers. "M32 is a weirdo", Bell continued. In addition, this finding might also resolve a secondary anonymity: Andromeda has a tiny satellite galaxy, M32, and researchers don't recognize where it created.

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