There is mounting evidence that galaxies get larger by merging with other galaxies.
Telescopes like the Hubble have captured dozens of interacting galaxies, including well-known ones like Arp 248.
The Andromeda Galaxy is the closest large galaxy to the Milky Way, and a new study shows our neighbor consumed other galaxies in two different epochs.
“A few years ago we discovered that on the very outskirts of Andromeda, a sign in the objects orbiting it suggests that the galaxy was not grazing, but was eating large amounts in two different epochs,” said Geraint Lewis of the University of Sydney.
Lewis is the lead author of a new paper entitled Chemo-dynamical substructure in the M31 inner halo globular clusters: Further evidence for an updated accretion event. tea Monthly Bulletins of the Royal Astronomical Society will publish the paper and it is currently available on the prepress website arxiv.org.
“This new result provides a clearer picture of how our local universe came together — it tells us that at least one of the large galaxies has had this sporadic feeding of small galaxies,” Lewis said in a press release.
Globular clusters are the focus of this research.
They are older associations of stars with 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. Globular stars, as they are called, are more common in a galaxy’s halo, while their counterparts, open star clusters, are found in the galactic disks.
The researchers behind this work identified a population of globular stars in Andromeda’s inner halo that all share the same metallicity. Metallicity refers to the elemental composition of stars, with elements heavier than hydrogen and helium being called metals in astronomy.
The orbs have lower metallicity than most stars in the same region, meaning they came from somewhere else, not Andromeda itself.
It also means they are older, since there were fewer heavy elements in the early universe than there are today.
Lewis named the collection of spheres the Dulai structure, which means black stream in Welsh.
The Dulais structure is likely a group of between 10 and 20 spheres that are not aligned with Andromeda’s rotation. But they’re not the only misaligned group of globular stars.
The Dulais structure is evidence that Andromeda fed on a cluster of globular stars sometime in the last 5 billion years. The other group is a subpopulation of globular stars, which is evidence of a second feeding event between 8 and 10 billion years ago.
According to Lewis and his co-authors, the globular clusters have lower metallicity and are also kinematically distinct from other clusters in the same region. The Andromeda galaxy rotates in one direction, and the Dulais structure moves in another.
To Lewis and his co-authors, the Dulais structure looks like the remains of a messy meal. It is a dark stream containing luminous star clusters. It’s further evidence that massive galaxies are merging to create gigantic displays across the universe, and that larger galaxies are consuming smaller spheres in a sort of galactic cannibalism.
“That then leads to the next question, well, what was actually consumed? Because it doesn’t look like it’s just one thing, it looks like it’s a collection of things that are all slowly being torn apart,” Lewis said.
“We’ve realized over the last few decades that galaxies grow by eating smaller systems — galaxies that small fall in, they get eaten — that’s galactic cannibalism.”
When these feeding events occurred, matter in the Universe was more concentrated. Ten billion years ago there may have been more such events across the universe. It’s one of the reasons astronomers are always asking for more powerful telescopes like the James Webb. You can see the light of ancient galaxies and see further into the past.
“We know that the universe was structureless when it was born in the Big Bang and is now full of galaxies. Were these galaxies born fully formed or did they grow?” said Lewis.
Astronomers would like to know the history of our own Milky Way. We all would. This is difficult through observation because we are embedded in it.
But Andromeda offers an opportunity to study galaxy evolution from an external perspective, and researchers like Lewis and his colleagues are taking full advantage of the opportunity.
As a spiral galaxy similar to the Milky Way, some of what astronomers learn about galaxy mergers from Andromeda may also apply to our galaxy.
But astronomers still have a long way to go before they can draw 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 implications for the bigger picture of galaxy formation,” said Lewis.
“We want to develop, at some level, a more accurate clock that will tell us when these events took place, because that’s something we need to include in our models of galaxy evolution.”
As it stands, Lewis and the other researchers only have 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 that will fill in the history of the orbs and how Andromeda consumed them.
Lewis isn’t absolutely sure we can call them spheres at this point, and he won’t be until there is more data. Hence the name “Dulais structure”.
“That will then allow us to create orbits of where things are going, and then we can start running the clock backwards and see if we get this coherent picture of when things are arriving,” he said.
“We couldn’t call it an object like a galaxy because we don’t actually know whether the signature we’re seeing comes from one large interfering object or from seven smaller interfering objects. So we refer to it as a structure rather than being a specific galaxy.”
There is obviously something going on with the Dulais structure and the Andromeda galaxy. But true to his scientific training, Lewis is cautious about making any firm conclusions at this point.
“It has 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 have yet to work that out.”
The authors clearly express their point of view in their work. “Interestingly, the orbital axis of this Dulais structure is closely aligned with that of the more recent accretion event recently identified using a subpopulation of globular clusters in Andromeda’s outer halo, strongly suggesting a causal relationship between the two. ” summarize the authors in their article.
“If this relationship is confirmed, a natural explanation for the kinematics of the globular clusters in the Dulais structure is that they represent the accretion of a major progenitor (roughly 10th11 solar masses) into Andromeda’s halo over the last few billion years, possibly occurring as part of a larger group incursion.
This article was originally published by Universe Today. Read the original article.
#nearest #galactic #neighbor #repeatedly #implicated #cannibalism #study #finds