A large group of stars with unusual trajectories pointed to the collision of the Milky Way with another galaxy more than eight billion years ago.
The shape and modern appearance of our Galaxy was largely determined by the catastrophe that happened to it even before the formation of the Sun - between 8 and 10 billion years ago. During this period, the Milky Way collided with a dwarf galaxy and swallowed it, and itself underwent serious structural changes. Scientists came to such conclusions by analyzing observation data from the Gaia space telescope.
It seems that the dead star cluster had an oblong shape, so it got the name "Sausage Gaia" (Gaia Sausage). She herself did not survive the collision, and only remains scattered across the Milky Way indicate her existence. Vasily Belokurov from Cambridge and his colleagues write about this in an article in the Monthly Notices of the Royal Astronomical Society. The publication is accompanied by a series of materials in the open electronic library arXiv.org, which reveal various details of this work.
The ESA Gaia space observatory conducts highly accurate astrometric observations, measuring the positions and speeds of the stars in the Milky Way. The authors relied on these data within 10 parsecs of the Sun, as well as on data from the Sloan Sky Survey (SDSS). They investigated the relationship between the content of elements heavier than helium (metals) in a star and its motion. During their work, scientists drew attention to a group of stars distinguished by a relatively high metallicity and high radial velocities. Unlike most stars in the Galaxy, they do not move at an approximately constant distance from its center, approaching or moving away from it. Moreover, the stars of this group form an oblong region - "Sausage Gaia".
On the speed diagram - 7000 stars measured by the Gaia probe, the elongated region of "Sausages" / copy; Belokurov (Cambridge, UK), Gaia (ESA) stands out.
Mergers and collisions The Milky Way has lived through its entire life, but the encounter with "Sausage Gaia" was one of the most dramatic. Its mass was more than 10 billion solar masses (about ten times lighter than the Milky Way), and at least eight star clusters remained from it in our Galaxy, which indicates a very decent size of the lost object. Computer simulations of the collision have shown how the stars of the Sausage find themselves in elongated orbits around the center of the Milky Way and are gradually absorbed by its disk.
Sergey Vasiliev