Huge flow of stars discovered in the southern sky

Stars in the newly discovered stellar stream.
Graphic: Meingast et al / Gaia DR2 (astronomy and astrophysics)

Scientists have discovered a nearby "stellar stream" containing thousands of stars spanning the southern sky. They made this discovery with the recent release of Gaia Sky survey data.

Stellar flows are essentially clusters of stars that have been separated, but still move in a correlated way, suggesting their related past. Such discoveries are interesting for the way they help astronomers understand not only the past of the Milky Way, but its current appearance.

"We know very little about our own galaxy," Stefan Meingast, the first author of the University of Vienna study, told Gizmodo. "Such fluxes that develop structures can be used as gravity probes in the Milky Way and give clues to the structure."

The latest publication of the Gaia mission of the European Space Agency included the largest star map ever created, describing the positions and movements of over a billion stars. Scientists have worked hard to sift through the data in order to gather information about the structure and history of our galaxy.

Stellar flow superimposed on a map of the Milky Way.
Graphic: Meingast et al / Gaia DR2 (astronomy and astrophysics)

The dataset allowed scientists to examine the position and speed of nearby stars in a river-shape – Gaia's wide field of vision allowed them to simultaneously analyze different properties of the stars. Their results revealed 200 stars in a creek only 325 light years from our sun. By extrapolation, they estimated that the watercourse could contain at least 4,000 stars and have a length of at least 1,300 light-years, according to the document published in Astronomy and Astrophysics.

Evidence suggests that stellar fluxes are the result of gravitational forces separating clusters of stars born together. Other recently discovered currents are associated with matter outside the Milky Way disk, in the region called Halo, including that supposedly responsible for an impending "dark matter hurricane". The apparent flow described in the new document is disk, however.

Meingast explained that uncertainties remain as to the age of the cluster, and that reported size is an estimate based on extrapolation. But, hopefully, other observations will reveal the true nature of this stellar flow.

Our position in the huge Milky Way makes it difficult to determine the shape of the galaxy. Understanding these streams and other structural complexities may one day allow us to understand our galaxy without having to leave it to have a bird's eye view.

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