The Andromeda galaxy "ate" the long-lost siblings of the Milky Way

The Milky Way's long-lost siblings were torn apart and devoured by our nearest major galactic neighbor – the Andromeda Galaxy – some two billion years ago, scientists have found. The massive galaxy, though largely tattered, left a rich trail of evidence – an almost invisible halo of stars larger than the Andromeda galaxy itself, and a separate compact M32 galaxy. This destroyed galaxy was the third largest member of the Local Group of galaxies, after the Milky Way and the Andromeda galaxies.

Using computer models, Richard D & # 39; Souza and Eric Bell of the University of Michigan in the US were able to work together to uncover this evidence, revealing this long-lost Milky Way sibling. Scientists have long known that this almost invisible, large halo of stars surrounding the galaxies contains the remains of smaller cannibalized galaxies. A galaxy like Andromeda was expected to consume hundreds of her smaller companions. The researchers thought that would make it difficult to learn about one of them.

Scientists found that although Andromaeda consumed many companion galaxies, most of the stars in Andromeda's outer faint halo contributed largely to the crushing of a single large galaxy. "It was a 'Eureka' moment. We realized that we could use that information from Andromeda's outer stellar halo to infer the properties of the largest of these rugged galaxies," D & Souza said. Lead author of the study, published in the journal Nature Astronomy.

"Astronomers have studied the Local Group ̵

1; the Milky Way, Andromeda, and their companions for so long – it was shocking to realize that the Milky Way had a big brother, and we never knew about it," Bell said. This galaxy, called M32p, which was ripped apart by the Andromeda galaxy, was at least 20 times larger than any other galaxy that linked to the Milky Way during its lifetime. M32p would have been massive, making it the third largest galaxy in the world Local group after the Andromeda and Milky Way galaxies

This work could also solve a long-standing mystery: the formation of Andromeda's enigmatic M32 satellite galaxy, the scientists say. They suggest that the compact and dense M32 is the surviving center of the Milky Way's long-lost siblings, like the indestructible pit of a plum. "While it (M32) looks like a compact example of an old, elliptical galaxy, it actually has many young stars, it's one of the most compact galaxies in the universe, and there is no other galaxy like this," Bell said.

The study may change the traditional understanding of galaxy evolution, researchers say. They realized that the disk of the Andromeda survived an impact with a massive galaxy, which would challenge the general wisdom that such large interactions would destroy disks and form an elliptical galaxy.