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Our galaxy has absorbed other galaxies over time and has grown rapidly. A kind of family tree now shows how this was done step by step.
Milky Way, photographed from Glaubberg.
Photo: Jonas Kuhn
According to astronomers, our Milky Way has engulfed several large galaxies for billions of years and has grown significantly as a result. A German-British research team has now reconstructed this process using so-called globular clusters in a kind of family tree. As a result, our natal galaxy merged with at least five large star systems 6 to 11 billion years ago, as a team led by Diederik Kruijssen of the University of Heidelberg writes in the ‘Monthly Notices of the Royal Astronomical Society’.
The researchers were also able to identify a previously unknown merger with a mysterious galaxy, which they named in honor of the legendary sea monster Kraken. The name suggests that the previous galaxy was difficult to identify and underline the massive impact the collision had.
Identify four previous galaxies
There are about 150 globular clusters in the Milky Way, in which up to a million stars are arranged in a certain way. Some of these groups formed within the Milky Way. Others, according to Kruijssen, come from galaxies that the Milky Way has absorbed over time.
When two galaxies merge, their globular clusters, to put it simply, are turned around. Therefore, it is relatively difficult for astronomers to determine which clusters they used to form a separate galaxy together. So far, astronomers have identified four previous galaxies that have merged with the Milky Way, explains Kruijssen.
The researchers analyzed the data using artificial intelligence.
The researcher and his team are now drawing an even more precise picture. Among other things, they used the European Space Agency’s Gaia Space Telescope, which measures the position and three-dimensional movement of stars and globular clusters. Although the clusters are scattered within the Milky Way, due to their specific movements within the Milky Way, their age of formation and their chemical composition, they can be assigned to a common precursor galaxy.
The researchers analyzed this data with the help of artificial intelligence they had previously trained on the results of complex computer simulations on the formation of galaxies such as the Milky Way. This allowed them to relatively accurately determine what mass a precursor galaxy had and when it collided with the Milky Way. In addition to the four galaxies already known, they found evidence of another: octopuses.
Kraken merged with the then still young Milky Way about 11 billion years ago. At the time, our galaxy only had about one twentieth of its mass, according to the researchers. As a result, the collision had a particularly strong effect. In total, the Milky Way incorporated five large galaxies with more than 100 million stars each, plus a dozen smaller ones with at least 10 million stars each.
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