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13 November 2020

par morgan hollis, Royal Astronomical Society

Scientists have known for some time that galaxies can develop through the fusion of smaller galaxies., but the ancestry of our own Milky Way galaxy is a long-standing mystery Today, an international team of astrophysicists succeeded in reconstructing the first complete family tree of our home galaxy by analyzing the properties of globular clusters orbiting the Milky Way with artificial intelligence. The work is published in the Monthly Notices of the Royal Astronomical Society

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Globular clusters are dense clusters of up to a million stars that are almost as old as the Universe itself The Milky Way is home to over 150 of these clusters, many of which formed in the smaller galaxies that merged to form the galaxy we live in today Astronomers have suspected for decades that the ancient ages of globular clusters would mean they could be used as «fossils» to reconstruct the first galaxy assembly histories. However, It is only with the latest models and observations that it has become possible to realize this promise

An international team of researchers led by Dr Diederik Kruijssen at the Center for Astronomy of the University of Heidelberg (ZAH) and Dr Joel Pfeffer of John Moores University in Liverpool has now succeeded in deducing the history of the Milky Way's merger and reconstructing its family tree, using only its globular clusters

To achieve this, they developed a suite of advanced computer simulations of the formation of galaxies resembling the Milky Way Their simulations, called E-MOSAICS, are unique because they include a complete template for training, the evolution and destruction of globular clusters

In the simulations, researchers were able to link the ages, the chemical compositions and orbital movements of globular clusters with the properties of the progenitor galaxies in which they were formed, there is more of 10 billion years. By applying this information to groups of globular clusters in the Milky Way, they were not only able to determine the number of stars contained in these progenitor galaxies, but also when they merged in the Milky Way.

“The main challenge in connecting the properties of globular clusters to the fusion history of their host galaxy has always been that galaxy assembly is an extremely complicated process., during which the orbits of the globular clusters are completely altered”, explains Kruijssen.

“To make sense of the complex system that remains today, so we decided to use artificial intelligence We trained an artificial neural network on E-MOSAICS simulations to relate the properties of the globular cluster to the history of the fusion of host galaxies. We tested the algorithm tens of thousands of times in the simulations and were amazed at the accuracy with which it was able to reconstruct the fusion histories of the simulated galaxies, using only their globular cluster populations.”

Inspired by this success, researchers set out to decipher the history of the Milky Way's fusion To achieve this, they used groups of globular clusters that would each have formed in the same progenitor galaxy based on their orbital motion. By applying the neural network to these groups of globular clusters, the researchers were not only able to predict the stellar masses and the fusion times of the progenitor galaxies with great precision, but it also revealed a hitherto unknown collision between the Milky Way and an enigmatic galaxy, who the researchers named “Kraken”

“Collision with Kraken must have been the most significant merger the Milky Way has ever seen”, ajoute Kruijssen «Previously, it was thought that a collision with the Gaia-Enceladus-Sausage galaxy, which took place about 9 billion years, was the biggest collision event. However, the merger with Kraken took place ago 11 billion years, when the Milky Way was four times less massive As a result, the collision with Kraken must have really transformed what the Milky Way looked like at the time”

Ensemble, these results allowed the team of researchers to reconstruct the first complete fusion tree of our galaxy In its history, the Milky Way has cannibalized about five galaxies with more than 100 million stars, and a fortnight with at least 10 million stars The most massive progenitor galaxies collided with the Milky Way between 6 and 11 billion years

Researchers expect their predictions to spur future studies to search for the remains of these progenitor galaxies “Debris from more than five progenitor galaxies has now been identified with current and future telescopes, it should be possible to find them all », conclut Kruijssen

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Milky Way, galaxy, star, research

News – FR – Milky Way family tree deciphered
Associated title :
Release the Kraken: astronomers building the first family tree & # 39; of the Milky Way discover its biggest collision & # 39;
Researchers decipher Milky Way family tree
Milky Way family tree deciphered

Source: https://phys.org/news/2020-11-family-tree-milky-deciphered.html

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