And from the cluster sprang forth a river: that’s not an attempt to be lyrical, just cosmic reality. When stars are born in a star cluster, they often only spend their youth in this group. As time goes on, the entire star cluster starts to feel the effects of gravitational forces from nearby galaxies. Like all stars of the galaxy, the cluster is flung around its core, deforming it over time, with the cluster becoming longer and longer and finally forming a stellar stream – a group of stars traipsing together through the galaxy.
There are already a few stellar streams known in our Milky Way, for example, the Arcturus Stream discovered in 1971 and the Monoceros Ring that wraps around the Milky Way several times. Now, using data from the ESA Gaia satellite, researchers have found another stellar stream flowing in the immediate vicinity of our Solar System, that is, in our galactic backyard. The stream is approximately 1300 light-years long. It’s about 160 light-years across and is approximately 325 light-years from our Sun. It covers a large part of the southern sky, up to 120 degrees. Researchers estimate that it could contain 4000 stars with a total of at least 2000 solar masses.
Researchers can’t say where its origin is quite yet, but they suspect an open star cluster or a so-called OB association, a looser form of a star cluster that is made up of hot stars of spectral classes O and B. The stream must be at least one billion years old and is moving away from the galactic plane at a speed of 11.4 kilometers per second. The discovery is interesting not only because it reveals more details about the Milky Way’s structure: the stellar stream is also a natural measuring instrument for the Milky Way’s gravitational field.