Stars found hidden in huge cloud wrapped around the Milky Way

The Magellanic stream is a cloud of dust and gas that wraps around our galaxy. It has long been thought to host stars, but they have never been seen until now

The Magellanic stream, in red, stretches nearly halfway around the Milky Way

A group of stars hidden in a vast stream of dust and gas that wraps around the Milky Way, which astronomers have been hunting for decades, has been found. These stars could give us clues about the history of two of the Milky Way’s closest dwarf galaxies, the Large and Small Magellanic Clouds, which feed this ribbon of material.

Up until now, the Magellanic stream, as it is known, appeared to be devoid of stars, despite astronomers predicting that they should exist. That in turn made it hard to measure the stream’s position and velocity.

Now, Vedant Chandra at Harvard University and his colleagues have identified 13 red giant stars, between 200,000 and 325,000 light years from Earth, that appear to have the same angular momentum and chemical composition as the gas of the Magellanic stream – strongly hinting that they formed from this material.

To make the discovery, the researchers combed through the Gaia catalogue, which contains the positions of and other information on more than a billion stars, filtering out any entries that seem to be moving within the Milky Way. They then further narrowed the field by looking for a group with a similar chemical composition to the Magellanic stream.

“For the first time we have this stellar counterpart [to the stream], which not only solves this decades-long mystery of why we haven’t found [such] stars yet,” says Chandra. “But it also gives us all of these very useful clues and information about how the gas itself could be moving.”

Knowing more about the stream will also help us understand the Large and Small Magellanic Clouds. Currently, we don’t know whether these orbit each other clockwise or anticlockwise, as results from simulations change depending on the position of the Magellanic stream stars. Finding these stars means that we can narrow down more accurate simulations of how the clouds, and the Milky Way, might evolve, says Chandra.

“It’s very exciting,” says Denis Erkal at the University of Surrey in the UK. “They’re finding this population of stars in the outer galaxy which we’ve been searching for for a while.”

However, some of the stars found by Chandra and his team appear to be metal-poor which, unlike the metal-rich stars in the stream, might mean they aren’t actually part of it. “They have shown that those metal-poor stars have similar kinematics to the Magellanic Clouds, so I think I buy their story that it’s connected in some way, but exactly how it’s connected I think is complicated,” says Erkal.


arXivDOI: 10.48550/arXiv.2306.15719

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