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Researchers used artificial intelligence to reconstruct the history of our Milky Way and found evidence of an ancient collision with a mysterious galaxy.
Researchers say the collision with the “Kraken” galaxy must have reshaped the Milky Way 11 billion years ago.
It was the largest collision suffered by the Milky Way galaxy, albeit far from unique.
Throughout its history, the Milky Way has cannibalized about five galaxies with more than 100 million stars and about fifteen with at least 10 million stars.
Dr Diederik Kruijssen of the University of Heidelberg Astronomy Center (ZAH) said: “The collision with Kraken must have been the most significant merger ever experienced by the Milky Way.
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“Earlier it was thought that a collision with the Gaia-Enceladus-Sausage galaxy, which occurred about 9 billion years ago, was the largest collision event.”
“However, the merger with Kraken happened 11 billion years ago, when the Milky Way was four times less massive. As a result, the collision with Kraken must have really transformed the appearance of the Milky Way at that time. “
The researchers used globular clusters – dense clusters of up to a million stars that are nearly as old as the Universe itself – to work out the history of the Milky Way.
The work was published in the Royal Astronomical Society’s monthly notices.
The Milky Way is home to over 150 globular clusters, many of which formed in the smaller galaxies that merged to form the galaxy we live in today. A
The researchers used the globular clusters as “fossils” to reconstruct the history of the Milky Way.
Using simulations, the researchers were able to relate the ages, chemical compositions and orbital motions of globular clusters to the properties of the progenitor galaxies in which they formed, more than 10 billion years ago.
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By applying these insights to groups of globular clusters in the Milky Way, they could not only determine how many stars these progenitor galaxies contained, but also when they merged into the Milky Way.
Kruijssen said: “The main challenge in linking the properties of globular clusters to the merging history of their host galaxy has always been that the assembly of the galaxy is an extremely messy process, during which the orbits of globular clusters are completely reshuffled.” ,
“To make sense of the complex system that remains today, we therefore decided to use artificial intelligence.
“We trained an artificial neural network on E-MOSAICS simulations to relate the properties of globular clusters to the merger history of the host galaxy.
“We tested the algorithm tens of thousands of times in simulations and were amazed at the accuracy with which it was able to reconstruct the merger histories of simulated galaxies using only their globular cluster populations.”
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