Milky Way’s family tree show that its biggest collision was with the Kraken galaxy


An international team of scientists have created the first complete family tree of our home galaxy using artificial intelligence.

Dr Diederik Kruijssen at the Center for Astronomy of Heidelberg University (ZAH) and Dr Joel Pfeffer at Liverpool John Moores University led a team of international scientists to create the first complete family tree of the Milky Way by analysing the properties of globular clusters orbiting the galaxy.

According to a statement released by the Center for Astronomy at the University of Heidelberg (ZAH) in Germany, globular clusters are dense groups of up to a million stars that are almost as old as the Universe itself.

 Milky Ways family tree show that its biggest collision was with the Kraken galaxy

The Milky Way as seen from Yellowstone National Park. Image courtesy: Neal Herbert/Flickr

While astronomers have, for decades, suspected that old globular clusters could be used as “fossils” to reconstruct early assembly histories of galaxies, latest models and observations have now made it possible to realise this promise.

Researchers have now managed reconstruct the family tree of the Milky Way. To create it, they used only its globular clusters. Study authors created a suite of advanced computer simulations of the formation of Milky-Way like galaxies called E-MOSAICS that are unique because they include a complete model for formation, evolution and destruction of globular clusters.

In the simulations, researchers were able to tell ages, chemical arrangements and orbital motions of globular clusters to the properties of galaxies that were formed more than 10 million years ago. By using these, they could not only determine how many stars these progenitor galaxies contained, but also when they merged into the Milky Way.


In genealogy, the progenitor is the founder of a family, line of descent, clan or tribe, noble house or an ethnic group.

Lead author Diederik Kruijssen explaied that they t6ested the algorithm tens of thousands of times on the simulations and were accurately able to reconstruct the merger histories of the simulated galaxies using globular cluster populations.

To decipher the merger history of the Milky Way, researchers used globular clusters and by applying neural network to these groups they revealed a previously unknown collision between the Milky Way and an enigmatic galaxy, which the researchers named “Kraken”.

Kruijssen stated that the collision with Kraken must have been the most significant merger for the Milky Way galaxy, adding that earlier, it was though that the Gaia-Enceladus-Sausage galaxy collision, which took place some 9 billion years ago, was the biggest.

Study authors found that the merger with Kraken took place 11 billion years ago, when the Milky Way was four times less massive. According to them, the collision of the Milky Way Galaxy with the Kraken must have transformed how the Milky Way looked like at the time.

The results of the study was published in the Monthly Notices of the Royal Astronomical Society.