Astronomers Have Mapped A Rare 'River Of Stars' Within The Milky Way That Formed One Billion Years Ago

Using the European Space Agency satellite Gaia, astronomers from the University of Vienna have mapped a new river of stars in the Milky Way that were found in the southern sky.

These 4,000 stars first appeared as a cluster approximately one billion years ago, and have since formed four rivers that meander around the periphery of the Milky Way, as Live Science reports. It is gravity which has caused this once serene cluster of stars to form a stellar stream around our galaxy, and at the present time these stars can be found traveling very close to Earth -- a mere 330 light-years away from our planet.

After the formation of most star clusters, the vast majority of the stars within them normally move away from each other. There are usually not enough stars to ensure that gravity will support them, and keep them together. Yet the 4,000 stars from this cluster have not been subjected to the gravitational forces that normally separate stars in other clusters, and have been traveling with each other for one billion years, continuing their movement together within this river of stars.

As João Alves -- one author of the new study on this river of stars -- explained,"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."

Astronomers first detected these bands by studying the movement of stars in 3D to determine what stars, if any, move together within close proximity to Earth. After combining this analysis with data from the Gaia satellite, they observed 200 stars flowing in a river. However, data taken from Gaia suggested that there were many more stars than this estimate -- and that approximately 4,000 stars were traveling together in a river.

Because this clusters of stars is so ancient, the stars within it have managed to complete four orbits around the galaxy. With one billion years of this movement, gravitational forces have created the river of stars that we see in the southern sky today.

As co-author Verena Fürnkranz noted, once astronomers from the University of Vienna studied these stars in greater detail, they were able to discover that they moved in a stream, according to a statement published in Astronomy & 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. It was so thrilling to be part of a new discovery."
This new discovery of a river of stars that stretches around the Milky Way has been elaborated upon in Astronomy & Astrophysics.