Milky Way's Neighbor Andromeda Galaxy May be a Cannibal Devouring Smaller Galaxies, Scientists Say

An international team of researchers led by an astronomer from the University of Sydney has found proof that the Andromeda galaxy, Milky Way's neighbor, is expanding due to its cannibalistic diet: smaller galaxies.

Lead author Professor Geraint Lewis from the University of Sydney explained that a few years ago, researchers found evidence in the objects orbiting Andromeda's distant outskirts that the galaxy has consumed massive amounts of galaxies in two different epochs.

This new finding helps to provide a fuller picture of how the local universe came to be; it reveals that little galaxies have occasionally been fed within one of the larger galaxies, according to Lewis.

Black Stream

The study was grounded on the discovery of globular clusters, a form of star structure in Andromeda that hailed outside the galaxy. Lewis dubbed this structure "Dulais", which is Welsh for "black stream."

A stream of darkness known as the Dulais Structure is lit up by star clusters that only orbit Andromeda. It is believed that they are the remnants of a recent, huge feeding event, providing evidence that galaxies grow by consuming their smaller counterparts.

"That then leads to the next question of, well, what was actually consumed? Because it doesn't look like it was just one thing, it looks like it's been a collection of things which are all being slowly torn apart," Professor Lewis said in a news release statement.

"We've come to realize over the last few decades that galaxies grow by eating smaller systems - so little galaxies fall in, they get eaten - it's galactic cannibalism."

The researchers claim that Andromeda has the remnants of two big feeding occasions. According to preliminary timelines, the recent feast took place during the last 5 billion years, but the older feed took place more than 8 to 10 billion years ago.

Given that the universe is 13.8 billion years old, it is possible that the two different events took place when the matter was concentrated and closer together.

Why Andromeda is Important

Professor Lewis and other astronomers are studying Andromeda to shed light on the formation and evolution of the Milky Way. The fact that we are seated inside our galaxy, obscuring observations, makes it challenging to observe it from Earth, while the distance from Andromeda gives astronomers the advantage of a panoramic vision.

Given that the Milky Way is a spiral galaxy that is similar in size to our own, the discovery might be able to explain how our galaxy evolved to be such a huge size.

Tim Adams from the University of Sydney and Yuan Li from the University of Auckland's research were the first to hint at the Dulais Structure's "leftover" origins.

A preprint of the team's research is accessible via arXiv and has been approved for publication in the journal Monthly Notices of the Royal Astronomical Society.