Dense river of stars found 1,000 light-years from Earth

Feb. 15 (UPI) -- Astronomers have discovered a river of stars flowing 1,000 light-years from Earth. The stellar river boasts some 4,000 stars and has been flowing for a billion years.

The river of stars is one of many stellar clusters found in the Milky Way, but its size, cohesion, age and proximity to Earth make it especially appealing to astronomers. Most stellar clusters identified by astronomers are smaller and younger.

Because stellar clusters are subject to the tidal forces created by the Milky Way's rotation, scientists can study the break up of stellar clusters to better understand the Milky Way's trajectory.

"Most star clusters in the Galactic disk disperse rapidly after their birth as they do not contain enough stars to create a deep gravitational potential well, or in other words, they do not have enough glue to keep them together," Stefan Meingast, an astronomer at the University of Vienna in Austria, said in a news release. "Even in the immediate solar neighborhood, there are, however, a few clusters with sufficient stellar mass to remain bound for several hundred million years. So, in principle, similar, large, stream-like remnants of clusters or associations should also be part of the Milky Way disk."

Researchers were able to study the movement of the stars in the stellar river using observation made by the European Space Agency's Gaia spacecraft. Launched in 2013, Gaia is working its way toward compiling the "book of the heavens" -- the largest and most precise 3D space catalog in history. As of April 2018, Gaia had measured nearly 1.7 billion stars in the Milky Way -- far more than the 1 billion stars ESA had hoped to survey with the craft.

The Gaia data showed the 4,000 stars in the stellar river coalesced a billion years ago and have been flowing together ever since. But the data also showed that since the river first formed, tidal forces have been pulling it apart.

"Identifying nearby disk streams is like looking for the proverbial needle in a haystack. Astronomers have been looking at, and through, this new stream for a long time, as it covers most of the night sky, but only now realize it is there, and it is huge, and shockingly close to the sun," said João Alves, an astrophysicist at Harvard University's Radcliffe Institute for Advanced Study. "Finding things close to home is very useful, it means they are not too faint nor too blurred for further detailed exploration, as astronomers dream."

Researchers described the stellar river this week in the journal Astronomy and Astrophysics.

"As soon as we investigated this particular group of stars in more detail, we knew that we had found what we were looking for: A coeval, stream-like structure, stretching for hundreds of parsecs across a third of the entire sky," said Verena Fürnkranz, doctoral student at the University of Vienna. "It was so thrilling to be part of a new discovery."

In addition to helping astronomer measure the movements of the Milky Way, the stellar river will also inform scientists understanding of the galaxy's gravitation fields, as well as aid in the measurement of the Milky Way's mass.