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Astronomers using ESA's Gaia satellite have discovered a large stream of stars that is currently crossing the immediate solar neighborhood at a distance of just 326 light-years. The stream contains at least 4,000 stars that have moved together in space since their formation, about a billion years ago.
Night sky centered on the galactic south pole in a so-called stereographic projection. In this special projection, the Milky Way bypasses the entire image in an arc. The stars in the stream are displayed in red and cover almost the entire southern galactic hemisphere, thus traversing many well-known constellations. Image credit: Meingast et al, doi: 10.1051 / 0004-6361 / 201834950 / Gaia DR2 control card.
"Most of the star clusters of our Milky Way disk disperse quickly after birth, because they do not contain enough stars to create deep gravitational potential. In other words, they do not have enough glue to keep them together, "said Stefan Meingast, astronomer at the Department of Astrophysics at the University of Vienna.
"Even in the immediate solar neighborhood, there are however some clusters with sufficient star mass to remain bound for several hundred million years."
"So, in principle, remnants of clusters or similar associations, of flux type, should also be part of the Milky Way disk."
Thanks to the precision of Gaia measurements, Mr. Meingast and his colleagues were able to measure 3D motion of stars in space.
When we carefully examine the distribution of nearby stars moving together, a particular group of stars, still unknown and unstudied, immediately caught the attention of the researchers.
It was a group of stars that exhibited precisely the expected characteristics of a group of stars born together but separated by the gravitational field of the Milky Way.
"Identifying nearby disk flows is like looking for the needle in a haystack," said Dr. João Alves, of the University of Vienna and University. Harvard.
"Astronomers have been watching and browsing this new stream for a long time because it covers most of the night sky, but only realize now that it is there and that it is huge and very close to the Sun."
"Finding objects close to home is very useful, it means that they are neither too weak nor too fuzzy to allow a more detailed exploration, as astronomers dream."
Due to the sensitivity limitations of the Gaia observations, their selection contained only about 200 sources.
Extrapolation beyond these limits suggests that the flow should have at least 4,000 stars, making the structure more massive than most known clusters in the immediate solar neighborhood.
"As soon as we studied this group of stars in more detail, we understood that we had found what we were looking for: a contemporary structure resembling a stream, extending over hundreds of parsecs on a third of the sky "Verena Fürnkranz, student at the University of Vienna.
"It was so exciting to be part of a new discovery."
The research is published in the journal Astronomy and astrophysics.
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Stefan Meingast et al. 2019. Expanded stellar systems in the solar neighborhood. II. Discovery of a stellar stream at 120 ° near Gaia DR2. A & A 622, L13; doi: 10.1051 / 0004-6361 / 201834950
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