Our neighbor Andromeda may have cannibalized another galaxy

Our closest galactic neighbor, the galaxy of Andromeda, seems to have a history of cannibalism. New research suggests that Andromeda engulfed another great galaxy about two billion years ago

Galactic stories are full of uncertainty and chaos – but how much chaos? New models of galactic formation demonstrate that Andromeda was able to undergo a great fusion with another galaxy, whose stars had a combined mass of about 25 billion times our own Sun. This hypothetical galaxy, whose remains exist as the Andromeda M32 satellite galaxy, would have been the third largest galaxy in our local group of galaxies.

The fusion would explain several observations simultaneously, according to the article published today in Nature Astronomy. Andromeda has a large stream of stars stretched into orbit, separated from his spiral arms, which is believed to have originated from a collision. It also has an orbiting satellite galaxy, M32, whose stars contain an abundance of elements heavier than hydrogen or helium. Andromeda also has a halo of stars with an excess of heavier elements. It also seems that one fifth of the Andromeda stars were formed two billion years ago, the newspaper reports.

Researchers used these clues in computer simulations to model a galaxy like Andromeda, with a similar mass and composition of stars with heavier elements. The simulation showed a collision with a large galaxy two billion years ago, in which Andromeda sucked the stars of the galaxy. Scientists call this galaxy M32p, whose corpse remains M32.

"This document is really a wonderful deployment of modern tools," said Gizmodo Sarah Tuttle, an astrophysicist at the University of Washington, who was not involved in the study . "The combination of simulation techniques and observations is beautifully executed to try to understand the truth of an event that occurred billions of years ago."

This study is just a model. During the astronomical era, we were obviously not there to observe the fusion, so it is only a hypothesis. "Although I find the evidence that they have put together in this very compelling article, it would be worthwhile to have detailed simulations that attempt to follow this model to validate it," said Monica Valluri, professor of Astronomy at the University of Michigan at Gizmodo.

So, although we can not travel back in time, astrophysical models like these can reveal strange stories, and potentially truths, about the history of our universe

[Nature Astronomy]