Analysis of the motion of several groups of stars in the halo of the Milky Way, carried out by a team of astronomers from the University of Groningen in the Netherlands, suggests that our Galaxy has experienced at least five small and one large-scale collisions in the past. The results of the study are presented in the Astrophysical Journal Letters.
The work is based on the second release of ESA's Gaia satellite, which provided the astronomical community with accurate information on the position and movement of millions of stars.
“Our goal is to understand how the Milky Way developed. The generally accepted mechanism for the evolution of galaxies is the merging of smaller structures that form larger stellar houses. However, the main question remains the size of the primary components: are many small galaxies merging or several large ones? And since most of the stars in the halo of the Milky Way are considered remnants of such events, my colleagues and I focused on these objects,”says Helmer Koppelman, lead author of the study.
Scientists initially identified information about stars located at a distance of 3,000 light years from the Sun, as for them "Gaia" collected the most accurate data on position and movement. They then filtered out stars from the Milky Way's disk that orbit the center of our Galaxy. As a result, astronomers were left with a group of about 6,000 luminaries living in the halo.
By calculating their trajectory, Helmer Koppelman and his team were able to identify groups of stars that share a common origin.
“We found five small clusters that we believe are remnants of five merge events. In addition, we were able to identify one large cluster with retrograde motion relative to the disk of the Milky Way. This indicates a merger with a large galaxy in the past, which we believe changed the structure of our Galaxy. As a result, we can say that the Milky Way was formed as a result of one large-scale and several small mergers,”explains Helmer Koppelmann.
Now astronomers plan to study stars more than 3,000 light-years from the Sun in order to identify more participants in the identified streams. Together with modeling the evolution of galaxies, the data obtained should provide exciting new hypotheses for the development of the Milky Way.
Nikolay Khizhnyak
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