Our galaxy, our home in the cosmos, has had a long and eventful life. Throughout history, it has collided and merged with many other galaxies and now these events, so difficult to unravel, have come to light thanks to technology.
An international team of astronomers has used complex computer models using artificial intelligence to create the first ancestral family tree of our galaxy, the Milky Way . The investigation revealed that the Milky Way, when it was in its formative stages, around 11 billion years ago, experienced its largest collision. The funny thing here is that, despite these intergalactic impacts were common in the past of our galaxy, the one with the enigmatic Kraken galaxy (its name is not random) was so large that it changed the appearance of our native galaxy, to forever.
Investigating globular clusters
Globular clusters are like the fossils of the early universe: they are collections of ancient, dense stars that are spherical in shape . They could be almost as old as the universe itself and can be used as stable information to reverse engineer galactic processes that occurred thousands of years ago. In any globular cluster, all of its stars formed at the same time, from the same gas cloud, which means that we can use their chemical composition to find out their origins. Hence, we will equip them with the fossils that paleontologists usually study.
Where we come from?
Using an artificial neural network to simulate globular clusters orbiting Milky Way-like galaxies (E-MOSAICS), astronomers have been able to recreate the entire lifespan of these globular clusters, of which there are about 150 in our galaxy.
“The main challenge in connecting the properties of globular clusters with the history of the merger of their host galaxy has always been that the assembly of galaxies is an extremely complicated process, during which the orbits of globular clusters are completely rearranged” Diederik Kruijssen of the University of Heidelberg (Germany) commented in the Monthly Notices of the Royal Astronomical Society that publishes the study.
In the simulations, the researchers were able to relate the ages, chemical compositions, and orbital motions of the globular clusters to the properties of the progenitor galaxies in which they formed, more than 10 billion years ago. It also allowed the researchers to gain insight into when they merged with the Milky Way.
El Kraken
The study revealed a previously unknown collision between the Milky Way and a mysterious galaxy that scientists named Kraken. The collision with Kraken had to have been the most significant merger the Milky Way has ever experienced.
“Previously, a collision with the ‘Gaia sausage’, which took place around 9 billion years ago, was thought to be the largest collision event. However, the merger with Kraken took place 11 billion years ago, when the The Milky Way was four times less massive . As a result, the collision with Kraken must have really transformed the look of the Milky Way at the time. “
Referencia: J M Diederik Kruijssen et al. Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations, Monthly Notices of the Royal Astronomical Society (2020). DOI: 10.1093/mnras/staa2452
