Astronomers have understood for years that galaxies are cannibalistic. Enormous galaxies like our own Milky Way have gotten mass by taking in smaller sized neighbours.
Now it appears like smaller galaxies like the Large Magellanic Cloud have also feasted on smaller neighbours.
Astronomers have revealed proof that the Large Magellanic Cloud (LMC), a dwarf satellite galaxy of the Milky Way, has taken in globular clusters. Globular clusters arent rather galaxies; theyre spherical clusters of thousands and even countless stars, and theyre the largest and most massive type of clusters. Theyre older and generally have lower metallicity than open clusters. Astronomers believe that globular clusters can remain partially coherent, even after being taken in by a larger galaxy like the LMC.
A group of Italian and dutch astronomers have published a paper providing their evidence that the LMC is growing more massive by soaking up globular clusters. The title is “A relic from a previous merger occasion in the Large Magellanic Cloud.” The lead author is Alessio Mucciarelli, a Professor in the Department of Physics and Astronomy at Bologna University, Italy. The paper is published in Nature Astronomy.
As our observing power got much better and much better, it turned out that many clusters consist of multiple populations of stars of various ages and metallicities. Now astronomers think that after the preliminary development of a GC, the cluster might have experienced another huge molecular cloud which activated another round of star development.
This NASA/ESA Hubble Space Telescope image shows a compact and far-off globular star cluster named NGC 7006. Its a Class 1 globular cluster, indicating its stars are highly concentrated rather than spread out and diffuse.
Even though GCs can have several populations of stars, their centers can hold together after they combine with a galaxy. Which reality is important to this research study.
The team of researchers behind this research study took a look at 11 various GCs in the Large Magellanic Cloud. Among them was NGC 2005, which has to do with 750 light-years far from the center of the LMC and consists of about 200,000 stars. The stars in NGC 2005 are different from other stars in the LMC: they include less zinc, copper, silicon, and calcium than the other 10 clusters in the LMC.
The astronomers believe that NGC 2005 is itself the relic of a smaller galaxy that was consumed by the LMC billions of years ago. The smaller sized galaxy had a low star development performance and a mass similar to a dwarf spheroidal galaxy. Over billions of years, the little galaxy was pulled apart and most of its stars spread out around. Not the core. After the rest of this small galaxy dissolved, the core remained mostly undamaged, and that core is called NGC 2005.
” We are in fact seeing an antique of an earlier merger.” D Massari, co-author, University of Groningen.
Composite image of NGC 2005 (left) and the Large Magellanic Cloud (right). The chemical structure of the stars in the globular cluster NGC 2005 differs from other stars in the Large Magellanic Cloud. It is the first evidence of combining dwarf galaxies outside our Milky Way.
Scientists use a technique called chemical tagging to identify populations of stars that share origins when theres no other observable proof that the population is related. “Chemical tagging is one of the couple of strategies that permit us to trace totally dissolved satellites, likewise in absence of any kinematically or spatially coherent antique, identifyingstars and clusters that were lost long earlier by ways of their anomalous chemical composition, on the other hand with the environment in which they live nowadays,” the authors compose.
The most vital parameter is a stars efficient temperature. The team behind this research study attempted to get past those issues by utilizing the 11 GCs as tracers.
GCs work well as tracers due to the fact that even after one is dissolved in the larger galaxy they merged with, their cores are still undamaged. “Such a cluster will keep a record of the characteristics of the environment in which it was born,” they compose.
The team of scientists compared the metallicity of the stars in NGC 2005 with 10 other GCs in the LMC, and with 15 older GCs in the Milky Way. As the table below shows, the metallicity of NGC 2005 stands apart.
NGC 2005s metallicity is different than the other GCs in the Large Magellanic Cloud and older GCs in the Milky Way. It has less Silicon, Calcium, zinc, and copper. Image Credit: Mucciarelli et al, 2021.
However exists other proof of mergers?
The team says that the metallicity abundances in NGC 2005 and the other GCs in the LMC show that they come from areas of substantially less effective star development than the remainder of the LMC. “This is typical of dwarf spheroidal (dSph) satellites of the Milky Way. Thus it is natural to search amongst them when trying to find an existing galaxy comparable to the putative progenitor of NGC 2005.”
Sagittarius and Fornax are the only dwarf spheroidal galaxies orbiting the Milky Way that had the ability to form GCs. Sagittarius metallicity resembles the LMCs, so isnt similar to NGC 2005. But Fornax is more of a match in chemical abundance and is also big enough to be a progenitor for something like NGC 2005. “Instead, Fornax has a stellar mass big enough ( 2 × 107 M) to host a population of 5 old GCs, four of them remaining in the very same mass variety as NGC 2005 (&& 1.3 · 105M.
These findings sufficed to encourage the team.
” We are really seeing a relic of an earlier merger,” said Davide Massari, a researcher at the INAF at the University of Groningen, and co-author of the paper from the University of Groningen. “And we have now convincingly shown for the very first time that small galaxies neighbouring our Milky Way have in turn developed from even smaller galaxies.”
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Astronomers have actually uncovered evidence that the Large Magellanic Cloud (LMC), a dwarf satellite galaxy of the Milky Way, has taken in globular clusters. Globular clusters arent quite galaxies; theyre spherical clusters of thousands or even millions of stars, and theyre the largest and most enormous type of clusters. Astronomers think that globular clusters can stay partially meaningful, even after being soaked up by a larger galaxy like the LMC.
The smaller sized galaxy had a low star development effectiveness and a mass similar to a dwarf spheroidal galaxy. Over billions of years, the little galaxy was pulled apart and many of its stars spread out around.
