If you live in the southern hemisphere, the next time you get the chance, go out and look at the night sky. Most of this celestial plain is covered with a cluster of stars that has been torn apart by the forces of the galactic tides and now passes before us like a giant river of more than 4,000 stars.
While this is visible, it has just been discovered, revealed by Gaia data that have resulted in the most accurate 3D map of the galaxy to date.
What makes this stellar flow exciting is its proximity to the Earth. There are only 100 parsecs left (326 light years), offering an unprecedented opportunity to scrutinize the dynamics of a disrupted cluster.
"Identifying nearby disk flows is like looking for the needle in a haystack." Astronomers have long been observing this new flow because it covers most of the night sky, but only now realize that he is there, and he is huge and very close to the Sun, "said astrophysicist João Alves of the University of Vienna.
"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."
Stars tend to form clusters in star nurseries, but they usually do not stay in clusters – perhaps up to a few hundred thousand years ago. It takes a lot of mass to create enough gravity to keep a cluster together – even small galaxies orbiting the Milky Way can be torn apart by its tidal forces and end up spreading in long rivers. stars revolving around the galactic core.
These can be difficult to see, as Alves says, because we need a lot of information to connect the stars to each other. But that's what Gaia has planned. Not only did he give precise locations in the 3D space for stars, he also provided us with their velocities, and enthusiastic astronomers used this data to identify stellar flows.
So, when astronomers from the University of Vienna noticed a group of stars moving together, they took a closer look. They discovered that the group bore the signatures of a group of stars that had been torn and was now a stream of stars.
Due to Gaia's sensitivity limitations, they were able to analyze only 200 stars in detail, but based on the interactions between the stars, the team extrapolated that the flow should contain at least 4,000 stars.
This starry river is important, about 200 parsecs (652 light-years) wide and 400 parsecs (1,305 light-years) long. These dimensions also help to estimate one's age.
The team argues that the flow is no different from the open Hyades cluster. At about 625 million years ago, the Hyades show signs of tidal tails; it is at the very beginning to be disturbed.
The researchers think that this current is older than the Hyades. Based on this comparison and a set of data on the stellar isochron (used to calculate the age of the stars), the team set the age of the flow to about 1 billion years old.
This means that it is completed around four complete orbits of the Milky Way (the Sun puts about 230 million years to orbit the galactic nucleus), which is enough time for it to happen. Stretches in its attenuated form.
"As soon as we studied this group of stars in more detail, we realized that we had found what we were looking for: a contemporary, stream-like structure, extending over hundreds of parsecs on a third of the sky, "said astronomer Verena Fürnkranz.
Most of the stellar flows identified to date in the Milky Way are actually in orbit outside the galactic disk and are much larger – but the location of this stream inside the disk could make it a valuable tool. For example, it could be used to limit the mass distribution of the Milky Way.
It could also help explain how galaxies get stars and test the gravitational field of the Milky Way, the researchers said.
With the help of Gaia data, they plan to look for more such flows in the night sky, hiding in the sight of all.
The research of the team was published in the journal Astronomy and astrophysics.