Astronomers Find Ghost Object Right Next To the Milky Way

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The Milky Way is not alone in our corner of the Universe. It is surrounded by dozens of small companion galaxies, some very close orbiting and others more distant. And now, researchers have announced the discovery of a new dwarf galaxy and it does not look exactly as we expected.

The object is called Antlia 2, or Ant 2, and does not appear to be there. Let us explain: it is huge, as large as a third of the Milky Way, but extremely weak. It is comparable in size to the Large Magellanic Cloud (LMC), one of our galactic neighbors visible to the naked eye, but is 10,000 times weaker. Basically, it is great for its brightness or too dark for its size.

"This is a ghost of a galaxy," said Gabriel Turrialba, lead author of the University of Cambridge study. "Objects as fuzzy as Ant 2 simply have not been seen before. Our discovery was only possible thanks to Gaia's data quality, "he said.

Gaia is the main European mission that is mapping the position of billions of stars in the Milky Way and beyond. Their high-precision measurements have enabled researchers to track the movement of millions of stars, which is how they discovered a group of distant stars moving together. After this first analysis, the researchers used the Anglo-Australian telescope to study another 100 stars, which allowed them to estimate the distance and mass of Ant 2.

It is located 130,000 light years from the Milky Way and is 13 million times more massive than the Sun. "The simplest explanation of why the object has so little mass today is that it is being disassembled by the gravitational tides of the Milky Way "Said study co-author Sergey Koposov of Carnegie Mellon University.” What remains unexplained, however, is the giant size of the object. Normally, when galaxies lose mass to the tides of the Milky Way, they shrink, they do not grow, "he concluded.

One possible explanation is that Ant 2 formed in a region of space where dark matter was not very dense and due to internal processes such as supernova explosions and stellar winds, the gas spreads. Over time, the stars formed on these edges, and the small galaxy received its current size. But this explanation requires very efficient explosions or dark matter behaving differently from our expectation. It is not clear at the moment what the dominant factor is.

"Compared with the rest of the 60 or so satellites in the Milky Way, Ant 2 is an eccentric," said Matthew Walker, a member of the study. "We are wondering if this galaxy is just the tip of an iceberg, and the Milky Way is surrounded by a large population of other near-invisible dwarf galaxies similar to this," he concluded. [ IFLS ]

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Ghost Galaxies

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