The stars that make up the Nix stream have been part of a magnet galaxy that orbited ours, until it was ‘sucked and stretched’ by the gravitational force of the Milky Way a billion years ago.
A survey, which used more recent data from the European Space Agency (ESA) Gaia mission, found a stellar current in the vicinity of the Solar System that was once part of a galaxy before it was “swallowed” by the Milky Way. The chain of Nix (in English, Nyx), named after the Greek goddess of the night, is described in a study published in Nature.
Launched in 2013, the Gaia satellite studies the movement, speed and distance of more than 1.7 billion stars to produce the most accurate 3D map of the Via Lctea. The researchers used this information to identify about 200 stars that, despite moving in the same direction as the accumulation disk of our galaxy, arrived here later, coming from outside.
According to the standard model of the evolution of the universe, galaxies grow by merging and absorbing smaller galaxies, the so-called accretion process. There is much evidence of this in the Milky Way, but all were identified using methods that search for objects that move differently in relation to the galactic disc, or stars with a different composition than those originally formed here. Finding a stream of stars that “fit” the Milky Way rotation is more difficult.
To carry out the discovery, the scientists applied deep learning methods to five dimensional measurements of the cataloged stars (two with angular coordinates, two with movement and parallax, which is the difference in the apparent position of an object seen by observers in different places), generating a score associated with the probability that the star has been accumulated during the formation of the galaxy.
With these data, the team found a group of 232 stars, all moving together in progressive motion – that is, in the direction of the galaxy’s rotation – and with similar chemical compositions. This group had not previously been associated with any other stellar current. Simulating the orbits of these stars a billion years ago, the researchers realized that they had different orbital properties from neighboring stars.
The team of researchers believes that Nix’s stellar current was once a galaxy, which, at some point in the long history of the Milky Way, was sucked and stretched as its stars began to orbit the center of the Milky Way. Repeating the research, but with broader parameters, the scientists found another group of stars that corresponded almost exactly to the flow of Nix and with equal chemical compositions. This second group would be the result of another passage of the same galaxy through the Milky Way.
Via: Science Alert
Stars Galxia Via Lctea Science & Space