Those who are in the southern hemisphere (Australia, Argentina, New Zealand …), are lucky enough to be able to look at the night sky and contemplate a cluster of stars torn by the galactic tides that now flow around us like a giant river of more than four thousand stars. This is what a team of astrophysicists from the University of Vienna (Austria) who now publishes their finding in the journal Astronomy & Astrophysics has discovered.
It is curious, but despite the fact that this river of stars is visible, it had not been discovered until now, thanks to the creation of the most accurate 3D map of the galaxies made with the Gaia data.
What makes this stellar stream fascinating is its proximity to Earth. It is only a hundred parsecs or 326 light-years away from our planet, offering an unprecedented opportunity to observe the dynamics of a disrupted cluster.
“Identifying nearby disk streams is like looking for the proverbial needle in a haystack. Astronomers have been looking through this new stream for a long time, as it covers most of the night sky, but it hasn’t been until now. realized that it is there, and it is huge, and it is surprisingly close to the Sun, “said astrophysicist João Alves, leader of the work.
“Finding things close to home is very useful, it means that they are not too faint or too fuzzy for a more detailed exploration, as astronomers dream”, continues the expert.
The course of the stars
Stars tend to form in clusters in stellar nurseries, but they generally do not stay clustered for long, perhaps up to a few hundred thousand years. It takes a lot of mass to accumulate enough gravity to hold a group together – even small galaxies that orbit the Milky Way can be ripped apart by tidal forces and end up spreading out in long rivers of stars that orbit the galactic core.
This can be difficult to see because we need a lot of information to be able to link the stars to each other . And it is what the Gaia space probe has provided. Not only has it given precise locations in 3D space for the stars, but it has also given us their speed, which is why astronomers have been using this data to identify stellar currents.
Noticing a group of stars moving en masse, they took a closer look. They found that the group bore the signature of a star cluster that had been torn apart, and now formed a star stream.
Due to the limitations of Gaia’s sensitivity, they were only able to analyze 200 stars in detail , but based on the interactions between the stars, the team believes that the stream must contain at least four thousand stars, 652 light years wide and 1,305 years old. long light.
According to the researchers, this stellar stream is older than the Hyades (the closest open cluster in the solar system). Based on this comparison, and a stellar isochron data set (which is used to calculate the age of stars), astrophysicists have established the age of the stellar stream at approximately 1 billion years.
“As soon as we investigated this group of stars in more detail, we knew that we had found what we were looking for : a wavy-type structure, which spans hundreds of parsecs in a third of the entire sky,” says Verena Fürnkranz, co-author of the study.
Most of the Milky Way stellar flows identified to date are actually orbiting outside the galactic disk, and are much larger, but the location of this river of stars within the disk could make it a very valuable tool.
For example, it could help shed light on how galaxies get stars and test the gravitational field of the Milky Way.
Reference: Stefan Meingast et al, Extended stellar systems in the solar neighborhood, Astronomy & Astrophysics (2019). DOI: 10.1051 / 0004-6361 / 201834950
