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The Milky Way Is Eating a Galaxy That’s Already Swallowed Another One

Like a galactic centipede.

For years, scientists have known that the Milky Way is a cannibalistic galaxy. 

Now, a team of astronomers from the University of Bologna discovered evidence that the neighboring Large Magellanic Cloud (LMC) is also a cosmic cannibal, meaning that it's no better than the Milky Way, a report by Science Alert explains.

The Milky Way has collided with many galaxies over the Universe's 13.8 billion-year lifespan and it is currently in the process of swallowing the Sagittarius Dwarf Spheroidal Galaxy, and the Large and Small Magellanic Clouds. It turns out that the Large Magellanic Cloud (LMC) gives as good as it gets, as the new observations, led by the University of Bologna's Alessio Mucciarelli, provide evidence that the LMC has also merged with another galaxy at some point in its past.

The researchers' new study, published in the journal Nature Astronomy, provides support for the theory of hierarchical assembly, which states that galaxies grow by subsuming smaller satellite galaxies. "This discovery," the researchers write, "is observational evidence that the process of hierarchical assembly has worked also in shaping our closest satellites."

Analyzing the remnant of an ancient galaxy

Specifically, the discovery came in the form of the observation and analysis of a globular cluster named NGC 2005, one of 60 globular clusters known to exist in the LMC. The astronomers observed that the chemical abundance ratios within this cluster were strikingly lower than those of other clusters found within the LMC. Based on these observations, the team decided to run simulations to see how such an outlier could have found its way to the LMC. The simulations showed that the most likely culprit would be a completely different galaxy, similar to satellites that currently neighbor the LMC. The LMC will have devoured that galaxy, leaving only NGC 2005 as a remnant of the ancient galaxy.

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"NGC 2005 is the surviving witness of the ancient merger event that led to the dissolution of its parent galaxy into the Large Magellanic Cloud, the only known case so far to be identified by its chemical fingerprints in the realm of dwarf galaxies," the researchers explain. "Our findings thus support the predictions on the self-similar nature of the process of galaxy formation by the standard cosmology on our closest satellite, and open a new way to investigate the assembly history of galaxies beyond the Milky Way via the chemical tagging of their globular cluster systems."

In other news, in a study from 2019, astronomers stated that the Milky Way may be eaten by its nearest neighbor, Andromeda. Though worry not, this wouldn't take place for another 4 billion years. Still, those findings alongside the new University of Bologna research both highlight the fact that the Universe is a constantly evolving beast, and that galaxies constantly consume one another, leaving only the ghosts of star systems behind. 

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