Scientists ahve found a whole stream of stars in the Milky Way – which appear to have come from somewhere else.

The discovery of the cluster of stars, known as "Nyx", could be an indication that a dwarf galaxy merged with the Milky Way, leaving behind evidence in the form of the newly discovered stars.

Researchers found the cluster asn they were looking at the movements of stars and dark matter as they move through our galaxy, in the hope of understanding where they came from and where they are going.

As they did so, researchers were looking for clusters that were moving together as they sailed through our galaxy. "If there are any clumps of stars that are moving together in a particular fashion, that usually tells us that there is a reason that they're moving together," said Lina Necib, a postdoctoral scholar in theoretical physics at Caltech, who led the study, in a statement.

To find the stars now known as Nyx, researchers combined two major projects that look to catalogue the workings of our galaxy. They were the "FIRE" project which is creating detailed simulations of the galaxy based on our full understanding of how they form and change over time, which worked alongside the Gaia space observatory's project to produce a full 3D map of our Milky Way and those stars beyond it, which hopes to catalogue about a billion stars.

Researchers hope to use both experiments to try and understand how the vast Milky Way that includes our own Sun came about. But the new breakthrough came from using the two together – they first tracked the movements of stars as they moved through the virtual galaxy, and watched for ways to understand whether they had formed within the galaxy or if they had arrived there from elsewhere, and then comparing that with real data from Gaia to understand where real stars are likely to have come from.

When the two pieces were combined, the researchers found thta there appeared to be a huge, unexpected structure in the data. There seemed to be a cluster of 250 stars that was rotating alongside the Milky Way, but heading towards its centre.

"Your first instinct is that you have a bug," said Necib in a statement. "And you're like, 'Oh no!' So, I didn't tell any of my collaborators for three weeks. Then I started realizing it's not a bug, it's actually real and it's new."

After checking through the literature to ensure it had not been discovered before, she realised that the cluster was actually a previously unknown stream of stars that had found their way into our galaxy and never been seen before. It was named Nyx, after the Greek goddess of the night.

Researchers now hope to conduct more studies of Nyx, to understand where it may have come from and how it has interacted with our Milky Way, as well as further research using FIRE and Gaia that will look for yet more details about the formation of other clusters.

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