American astronomers adapted the latest computer modeling method to process real data from telescopes and accidentally discovered a previously unknown foreign cluster of stars in the Milky Way.
A team of scientists led by Lina Nesib of the California Institute of Technology, using computer models and artificial intelligence, processed huge amounts of data from the space observatory Gaia, discovered a "quiet" large cluster of stars, which does not reveal its extragalactic origin. The researchers reported on the grandiose results in the journal Nature Astronomy.
Nesib and her team are exploring how galaxies formed and evolved from early times to the present. Their method is to create a complex model of the galaxy, which includes millions of stars, for each of which, in addition to coordinates, mass and brightness, three components of velocity in x, y, and z are known. If we take into account the mutual influence of the stars on each other, all the projections of the forces that act on them, as well as billions of years since the Big Bang, the sum is an unimaginably huge set of data.
As part of the FIRE project, a team of astronomers has been leveraging all available supercomputer power since 2014, and is also using machine learning to create virtual models of galaxies similar to the Milky Way.
The FIRE project is not only about beautiful pictures and believable simulations. Without such a tool, astronomers would never have deciphered observational data from the Gaia space observatory, launched in 2013 by the European Space Agency, and data from other large-scale missions. Gaia donated a 3D detailed map of 7 million stars in the Milky Way and beyond to the scientific community. To process such a dataset without modeling and artificial intelligence algorithms is like manually counting grains of sand on a beach.
Combining observations and computer simulations has allowed scientists to find stars that, in their opinion, ended up in our galaxy due to its merger with less massive neighbors. Digging through the catalogs, scientists did not find a description of the discovered stars and, like children, were delighted with the discovery. The found cluster of 250 stars was named Nyx, after the Greek goddess of the night.
To be sure of the foreign origin of Nyx, the researchers checked whether the model could "see" other stars born outside the Milky Way, already known to scientists. The identification of the Gaia-Enceladus galaxy, which the Milky Way swallowed 6-10 billion years ago, and the Helmi Stream dwarf galaxy, which also merged with ours in the distant past, became the "test task" for the model.
The probability of the capture of stars from these galaxies by the Milky Way, which was given by the model, was taken by scientists as a reference and compared with the probability of the extragalactic origin of Nyx. Everything pointed to the fact that Nyx is the remnants of a once swallowed galaxy.
The researchers note that the structure of the Knicks is rather unusual, and the cluster would be very difficult to see without machine learning. Inspired by the success, the Nesib team plans to “scan” another 100 million stars using a computer model that the Gaia Observatory will map by 2021. The Nyx cluster will continue to be studied using powerful ground-based telescopes. Scientists want more information about the chemical composition, masses and luminosity of stars in order to date the merger of Nyx and the Milky Way, and perhaps find the "home" of Nyx.