Our nearest galactic neighbor engages in ‘cannibalism’ over and over again, study finds – ScienceAlert

There is a growing body of evidence that galaxies grow large by merging with other galaxies.

Telescopes like Hubble have captured dozens of interacting galaxies, including those known as Arp 248.

The Andromeda Galaxy is the closest large galaxy to the Milky Way, and a new study shows that our neighbor has consumed other galaxies at two different times.

“A few years ago, we discovered that on the far outskirts of Andromeda, there was a signal in the objects orbiting it that the galaxy had not been grazing, but had eaten large amounts at two different times.” said Geraint Lewis of the University of Sydney.

Lewis is the lead author of a new paper titled “Chemodynamic substructure in M31 inner halo globular clusters: further evidence for a recent accretion event.“The Monthly Notices of the Royal Astronomical Society will publish the document, and it is currently available at prepress site arxiv.org.

“What this new result does is provide a clearer picture of how our local universe came together: it’s telling us that at least in one of the large galaxies, there has been this sporadic feeding of small galaxies,” Lewis. said in a press release.

Globular clusters they are the center of this research.

They are older associations of stars that have lower metallicity. There are at least 150 in the Milky Way, probably more. They play a role in galactic evolution, but the role is not clearly understood. Globulars, as they are known, are more common in a galaxy’s halo, while their counterparts, open clusters, are found in galactic disks.

The researchers behind this work identified a population of globules in Andromeda’s inner halo that all have the same metallicity. Metallicity refers to the elemental composition of stars, with elements heavier than hydrogen and helium called metals in astronomy.

Globulars have a lower metallicity than most stars in the same region, meaning they come from elsewhere, not from Andromeda itself.

It also means they are bigger, since there were fewer heavy elements in the early Universe than now.

Lewis called the collection of balloons the Dulai structure, which means black stream in Welsh.

The Dulais structure is probably a group of 10 to 20 globulars misaligned with Andromeda’s rotation. But they are not the only group of misaligned globulars.

The Dulais structure is evidence of Andromeda feeding on a group of balloons sometime in the last 5 billion years. The other group is a subpopulation of globulars that is evidence of a second feeding event between 8 and 10 billion years ago.

According to Lewis and his co-authors, globular clusters have a lower metallicity and also differ kinematically from other clusters in the same region. The Andromeda Galaxy spins one way and the Dulais structure moves a different way.

To Lewis and his co-authors, Dulais’ structure looks like the remains of a messy meal. It is a dark stream containing vibrating star clusters. It’s further evidence that massive galaxies merge to produce gigantic screens across the Universe, and that larger galaxies consume smaller globular ones in a kind of galactic cannibalism.

“That leads to the next question: 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 that are slowly breaking down.” said Lewis.

“In the last few decades we’ve realized that galaxies grow by eating smaller systems, so small galaxies fall in, they get eaten, it’s galactic cannibalism.”

When these feeding events occurred, the matter in the Universe was more concentrated. Ten billion years ago, there could have been more of these events throughout the Universe. This is one of the reasons why astronomers want ever more powerful telescopes like the James Webb. They can see the light of ancient galaxies and look further back in time.

“We know that the Universe had no characteristic features at its birth big bang, and today it is full of galaxies. Were these galaxies born fully formed or did they grow?” Lewis said.

Astronomers would like to know the history of our own galaxy, the Milky Way. We all would. This is difficult to do through observations because we are embedded in them.

But Andromeda offers an opportunity to study the evolution of galaxies from an outside perspective, and researchers like Lewis and his colleagues are making the most of it.

As a spiral galaxy similar to the Milky Way, some of what astronomers learn about Andromeda galaxy mergers can also be applied to our galaxy.

But astronomers have more work to do before they can draw any conclusions about the Milky Way. Or about mergers and consumption in general. The goal is a more detailed timeline of galactic evolution throughout the Universe.

“What we want to know is, has the Milky Way done the same or is it different? Both have interesting consequences for the big picture of how galaxies form,” Lewis. said.

“We want, at some level, to find a more precise clock that tells us when these events occurred because that’s something we need to include in our models of how galaxies evolve.”

As it stands, Lewis and other researchers have only a two-dimensional historical view of Dulais’ structure.

The dimensions are speed and chemistry. Finding the distances of all these objects will provide a third dimension, which will fill in the story of the globulars and how Andromeda consumed them.

Lewis isn’t entirely sure we can call them globular at this point, and won’t be until more data is available. Hence the name “Dulais Structure”.

“This will allow us to calculate orbits, where things are going, and then we can start running the clock back and see if we can get this consistent picture of when things fell,” he said. said.

“We couldn’t call it a galaxy-like object because we don’t actually know if the signature we see is from one large object being disrupted or seven smaller objects being disrupted. That’s why we refer to itself as a structure instead. being a particular galaxy.”

There is obviously something going on with the Dulais structure and the Andromeda galaxy. But true to his scientific background, Lewis is cautious about firm conclusions at this stage.

“It’s opened a new door in terms of our understanding,” Lewis said in a press release. “But exactly what he’s telling us, I think we’ve yet to sort out.”

The authors make their case clearly in their paper. “Interestingly, the orbital axis of this Dulais structure is closely aligned with that of the youngest accretion event recently identified using a subpopulation of globular clusters in Andromeda’s outer halo, strongly suggesting a relationship causal between the two.” the authors summarize in their paper.

“If this connection is confirmed, a natural explanation for the kinematics of Dulais-structured globular clusters is that they trace the accretion of a substantial progenitor (about 10¹¹ solar masses) in Andromeda’s halo over the past billion years, which may have occurred as part of a larger cluster collapse.”

This article was originally published by universe today. read the original article.