(ORDO NEWS) — There is growing evidence that galaxies are growing in size, merging with other galaxies.
Telescopes like Hubble have captured dozens of interacting galaxies, including the famous Arp 248.
The Andromeda Galaxy is the closest large galaxy to the Milky Way, and a new study shows that our neighbor has been gobbling up other galaxies in two different eras.
“A few years ago, we found that in the far fringes of Andromeda, in objects orbiting it, there was a sign that the galaxy was not grazed, but eaten in large quantities in two different eras,” said Geraint Lewis of the University of Sydney.
Lewis is the lead author of a new paper entitled “Chemo dynamic Substructure in the Inner Halo of M31 Globular Clusters: Further Evidence for a Recent Accretion Event.”
The paper will be published in the Monthly Notices of the Royal Astronomical Society and is currently available on the prepress site arxiv.org.
“This new result gives a clearer picture of how our local universe came together, which tells us that at least one of the large galaxies was sporadic feeding of small galaxies,” Lewis said in a press release.
Globular clusters are at the center of this study.
These are older associations of lower metallicity stars. There are at least 150 of them in the Milky Way, and maybe more.
They play a role in galactic evolution, but this role is not fully understood. Globular clusters are known to be more common in galactic halos, while their counterparts, open clusters, are found in galactic disks.
The researchers involved in this work identified a population of globular clusters in the interior of Andromeda. halo that they all have the same metallicity.
Metallicity refers to the elemental composition of stars, with elements heavier than hydrogen and helium being called metals in astronomy.
The globules have a lower metallicity than most stars in the same region, which means they came from somewhere else and not from Andromeda itself.
This also means they are older, as there were fewer heavy elements in the early universe than there are now.
Lewis called the collection of globular structures the Dyulai structure, which means “black stream” in Welsh.
The Dule structure is probably a group of 10–20 spherules offset from Andromeda’s rotation. But this is not the only displaced group of spherical formations.
Dula’s structure suggests that Andromeda was fed by a group of globular formations sometime in the last 5 billion years. The other group is a subpopulation of globular clusters, indicative of a second feeding between 8 and 10 billion years ago.
According to Lewis and his co-authors, globular clusters have a lower metallicity and are also kinematically different from other clusters in the same region. The Andromeda Galaxy rotates in one direction, and the Dule structure in the other.
To Lewis and his coauthors, Dulay’s structure appears to be the remnants of a messy dinner. It is a dark stream containing bright star clusters.
This is further evidence that massive galaxies are merging to form giant images across the universe, and that larger galaxies are engulfing smaller globular bodies in a kind of galactic cannibalism.
“This leads to the next question, what was actually eaten? Because it doesn’t look like one thing, it looks like it was a collection of things that are slowly being torn apart,” Lewis said.
“We have come to the conclusion that in the last few decades, when galaxies grow by eating smaller systems so that small galaxies get in, they get eaten this is galactic cannibalism.”
When these feeding events occurred, the matter in the universe was more densely concentrated. Ten billion years ago, there could have been more such events in the universe.
This is one of the reasons why astronomers need more and more powerful telescopes like James Webb. They can see light from ancient galaxies and see into the past.
“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 grown? Lewis said.
Astronomers would like to know the history of our own Milky Way galaxy. We would all like to. This is difficult to do with observations because we are built into it.
But Andromeda provides an opportunity to study the evolution of the galaxy from an outside perspective, and researchers like Lewis and his colleagues are taking full advantage of it.
Since it is a spiral galaxy similar to the Milky Way, some of what astronomers are learning about the Andromeda merger could apply to our galaxy as well.
But astronomers still have a lot of work to do before they can draw conclusions about the Milky Way. Or about mergers and acquisitions in general. The goal is a more detailed timeline of galactic evolution in the universe.
“We want to know if the Milky Way did the same or differently? Both have interesting implications for the big picture of how galaxies form,” Lewis said.
“We want, at some level, to have a more accurate clock to tell us when these events happened, because that’s one thing we need to include in our models of galaxy evolution.”
At present, Lewis and other researchers only have a two-dimensional historical understanding of the Dule structure.
Measurements are speed and chemistry. Finding the distances to all of these objects would provide a third dimension that would complete the story of the globulars and how Andromeda devoured them.
Lewis isn’t entirely sure we can call them globular at this point, and he won’t be until there’s more data. Hence the name “Dule Structure”.
“This will allow us to calculate the orbits where things are going and then we can run the clock backwards and see if we can get that coherent picture when something fell,” he said.
“We can’t call it a galaxy-like object because we don’t really know if the signature we’re seeing is the result of the destruction of one large object or seven smaller ones. objects are destroyed. That’s why we call it a structure and not a single galaxy.”
Clearly something is going on with the Dule structure and the Andromeda galaxy. But true to his scientific background, Lewis is wary of firm conclusions at this stage.
“This 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 find out.”
The authors clearly state their position in their article. “Interestingly, the orbital axis of this Dule Structure is closely related to that of a younger accretion event recently identified using a subpopulation of globular clusters in Andromeda’s outer halo, strongly suggesting a causal relationship between the two. “, the authors summarize in their article.
“If this link is confirmed, then the natural explanation for the kinematics of globular clusters in the Dule structure would be that they trace the accretion of a significant progenitor (about 1011 solar masses) into the Andromeda halo over the past few billion years, which could have happened as part of the fall of a larger group.”
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