The first complete family tree of our home galaxy

Globular clusters (GCs) were formed when the Milky Way experienced a phase of rapid assembly. The Milky Way hosts over 150 such groups. Most of these clusters are made up of small galaxies, which merge to form the galaxy we live in today.

For decades, the old era of spherical clusters has been considered a ‘fossil’ for reconstructing the early assembly history of galaxies. However, it is only with the latest models and comments that it has become possible to realize this promise.

Dr. at the Center for Astronomy of Heidelberg University (ZAH). An international team of researchers led by Diederik Kruijssen and Dr. John Moores University at Liverpool. Joel Fafar has now managed to anticipate the merger of the Milky Way. They have successfully reconstructed the first complete family tree of our home galaxy by analyzing the properties of spherical clusters, orbiting the Milky Way with artificial intelligence.

Scientists achieved this using newly developed computer simulations of the formation of Milky Way-like galaxies.

Called E-MOSAICS, the simulation includes a complete model for the formation, growth, and destruction of spherical groups.

In the simulation, researchers related the age, chemical compositions, and orbital motion of spherical clusters in the properties of the ancestral galaxies in which they formed more than 10 billion years ago. By applying these insights to clusters of spherical clusters in the Milky Way, they determined the number of stars of these ancestral galaxies. He also got an idea when the Milky Way merged.

Dr. at the Center for Astronomy at Heidelberg University (ZAH). Diederik Kruijssen said, “The main challenge of adding the properties of spherical clusters in the history of the merger of your host galaxy has always been that galaxy assembly is an extremely convoluted process, during which the orbits of spherical clusters are completely altered.”

“To understand the complex system that survives today, we decided to use artificial intelligence. We trained an artificial neural network on e-mosaic simulations to relate spherical cluster properties to the history of host galaxy mergers. We tested the algorithm thousands of times on the simulation. We were amazed at how it was able to recreate the merger history of simulated galaxies, using only its spherical cluster population. ”

After obtaining these results, scientists set out to determine the history of the merger of the Milky Way. To do this, they used clusters of spherical clusters that are thought to form in the same ancestral galaxy based on their orbital motion.

By applying neural networks to these clusters of spherical clusters, scientists could predict the high mass and merger times of ancestor galaxies. It also revealed a seemingly unknown collision between the Milky Way and a mysterious galaxy, named “Kraken”.

Kruijssen said, “The confrontation with Kraken was the most significant merger of the Milky Way that had ever been experienced. Earlier, it was thought that the collision with the Gaia – Enceladus – Sausage galaxy occurred some 9 billion years ago. However, the merger with Kraken occurred 11 billion years ago, when the Milky Way was four times less massive. As a result, the collision with the Kraken was actually replaced by what the Milky Way looked like at the time. ”

Throughout its history, the Milky Way has described five galaxies with over 100 million stars and fifteen with at least 10 million stars. The largest ancestor galaxies collided with the Milky Way 6 to 11 billion years ago.

According to scientists, the study may help encourage future studies in the discovery of the remains of these ancestor galaxies.

Journal reference:
  1. JM Diderick Kruijsen et al. Kraken reveals himself – the merger history of the Milky Way reunited with the e-Mosaic simulation, the Royal Astronomical Society’s Monthly Notices (2020). DOI: 10.1093 / mantra / staa2452

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