There is a growing body of evidence that galaxies grow by merging with other galaxies.
Telescopes like Hubble have captured dozens of interacting galaxies, including well-known ones like Arp 248.
The Andromeda Galaxy is the nearest large galaxy to our 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 in the far reaches of Andromeda, there was a sign in the objects orbiting it that the galaxy was not grazing, but had eaten large amounts at two different times,” said Geraint Lewis from the University of Sydney.
Lewis is the lead author of a new paper titled “Chemodynamic substructure in the inner globular clusters of M31: Further evidence for a recent accretion event.” The Monthly Notices of the Royal Astronomical Society will publish the paper and it is currently available on the preprint site arxiv.org.
“What this new result does is provide a clearer picture of how our local universe has come together — it tells us that in at least one of the large galaxies, there has been this sporadic feeding of small galaxies,” Lewis said in a press release. release.
Globular clusters are the focus of this research.
They are older star compounds that have lower metallicity. There are at least 150 in our Galaxy, probably more. They play a role in galactic evolution, but the role is not clearly understood. Globules, as they are known, are more prevalent in the halo of a galaxy, 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 referred to as metals in astronomy.
The globules have a lower metallicity than most stars in the same region, meaning they came from elsewhere, not from Andromeda itself.
It also means that they are older since there were fewer heavy elements in the early Universe than there are now.
Lewis named the collection of beads the Dulai Structure, which means black stream in Welsh.
The Dulais structure is likely a group of between 10 and 20 globules that are misaligned with Andromeda’s rotation. But they are not the only misaligned group of bowlers.
The Dulais structure is evidence that Andromeda fed on a group of globules sometime in the last 5 billion years. The other group is a subpopulation of globules that is evidence of a second feeding event 8 to 10 billion years ago.
According to Lewis and his co-authors, globular clusters have a lower metallicity and are also kinematically distinct from other clusters in the same region. The Andromeda galaxy rotates one way and the Dulais structure moves another.
To Lewis and his co-authors, the Dulais structure resembles the remains of a messy meal. It is a dark stream that contains living star clusters. It’s further evidence that massive galaxies are merging to create giant screens across the Universe, and that larger galaxies are consuming smaller globules in a type of galactic cannibalism.
“That then leads to the next question, what was actually consumed? Because it doesn’t look like it was just one thing, it looks like it was a collection of things that are all slowly disintegrating,” Lewis said.
“We’ve realized in the last few decades 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 tightly packed. Ten billion years ago, there may have been more of these events throughout the Universe. That’s one of the reasons astronomers want more and more powerful telescopes like the James Webb. They can see light from ancient galaxies and look further back in time.
“We know that the Universe was featureless at its birth in the Big Bang, and today it is full of galaxies. Were these galaxies born fully formed or have they grown?” Louis 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 it.
But Andromeda presents an opportunity to study galaxy evolution from an outside perspective, and researchers like Lewis and his colleagues are taking full advantage.
As a spiral galaxy similar to our own, some of what astronomers are learning about galaxy mergers from Andromeda may apply to our galaxy.
But astronomers have more work to do before they can draw any conclusions about the Milky Way. Or in general for mergers and acquisitions. A more detailed timeline of galactic evolution across the Universe is the goal.
“What we want to know is, has the Milky Way done the same or is it different? Both have interesting implications for the overall picture of how galaxies form,” Lewis said.
“We want, at some level, to find a more accurate clock to tell us when these events happened because that’s one thing we need to include in our models of how galaxies evolve.”
As it stands, Lewis and the other researchers have only a two-dimensional historical view of the 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 orbs and how Andromeda consumed them.
Lewis isn’t entirely sure we can call them spherical at this point, and it won’t be until more data is available. Hence the name “Dula Structure”.
“This will then allow us to work out trajectories, where things are going, and then we can start to run the clock back and see if we can get this coherent picture of when things fell,” he said.
“We couldn’t call it a galaxy-like object because we don’t really know if the signature we’re seeing is from one large interrupting object or seven smaller interrupting objects. So we sort of refer to it as a structure instead of it being a particular galaxy’.
Apparently something is going on with the Dulais structure and the Andromeda galaxy. But true to his scientific training, Lewis is cautious about drawing firm conclusions at this stage.
“It opened a new door in terms of our understanding,” Lewis said in a press release. “But exactly what it’s telling us, I think we still have to process.”
The authors clearly state their case in their paper. “Strangely, the orbital axis of this Dulais structure is closely aligned with that of the younger accretion event recently detected using a subpopulation of globular clusters in Andromeda’s outer halo, and this strongly suggests a causal relationship between the two,” the authors summarize in the paper their.
“If this connection is confirmed, a natural explanation for the kinematics of globular clusters in the Dulais structure is that they trace the growth of an important progenitor (about 1011 solar masses) in Andromeda’s halo over the past billion years, which may have occurred as part of a larger mass collapse.”
This article was originally published by Universe Today. Read the original article.