Researchers decipher Milky Way family tree

Astrophysicists have used complex computer models powered by artificial intelligence to produce an ancestral family tree of the Milky Way.

Research has revealed that the Milky Way, when it was in its infancy around 11 billion years ago, experienced its biggest collision ever.

Intergalactic collisions were common in our galaxy’s past, but the impact of the enigmatic Kraken was so great that it changed the very appearance of our original galaxy.

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Other notable collisions and mergers are the “Helmi Streams” event about 10 billion years ago and the smaller Sequoia event about a billion years later.

Shortly after Sequoia came Gaia-Enceladus, nine billion years in the past, which was previously believed to be the Milky Way’s greatest collision, before astronomers found Kraken.

Dr Diederik Kruijssen, co-author of the Heidelberg University study, said: “The collision with Kraken must have been the most significant merger the Milky Way has ever seen.

“ Previously, it was believed that a collision with the Gaia-Enceladus-Sausage galaxy, which took place around nine billion years ago, was the largest collision event.

However, the merger with Kraken took place 11 billion years ago, 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. ”

Scientists have known for some time that galaxies can develop through the merging of smaller galaxies, but so far the ancestry of our own galaxy has been a mystery.

To determine how our ancient galaxy reached its massive size of over 100,000 light years in diameter with spiral arms and a peanut-shaped core, researchers turned to AI.

A neural network has been trained by academics to analyze globular clusters – dense clusters of up to a million stars.

These can act as the building blocks of vast galaxies and can date back to the dawn of the Universe, around 14 billion years ago.

The Milky Way is home to more than 150 of these clusters, many of which formed in the smaller galaxies that merged to form the galaxy we live in today.

During 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.

The most massive progenitor galaxies collided with the Milky Way between six and 11 billion years ago, the researchers say.

For decades, astronomers have suspected that ancient clusters could be used as fossils to reveal the chronology of events in the Milky Way.

An international team of researchers led by Dr Diederik Kruijssen, at the Center for Astronomy at the University of Heidelberg (ZAH), and Dr Joel Pfeffer, at the University of Liverpool John Moores have developed a computer simulation of the Milky Way , called E-Mosaics, to help solve the mystery.

In the simulations, the researchers were able to relate the ages, chemical compositions and orbital motions of globular clusters to the primitive galaxies that created them more than 10 billion years ago.

By applying this knowledge to groups of globular clusters sitting in the Milky Way, they could determine the number of stars contained in these progenitor galaxies.

It also gave researchers a better understanding of when they merged with the Milky Way. By mapping them all, the researchers built a complex picture of the galaxy’s interactions, leading to the Milky Way we see today.

The research is published in the Monthly Notices of the Royal Astronomical Society.