Far out cosmology: our galaxy is huge (Introduction)

by David Turell , Saturday, November 14, 2020, 23:24 (1468 days ago) @ David Turell

More findings on how it got so big:

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

"Scientists have known for some time that galaxies can grow by the merging of smaller galaxies, but the ancestry of our own Milky Way galaxy has been a long-standing mystery. Now, an international team of astrophysicists has 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.

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"In the simulations, the researchers were able to relate the ages, chemical compositions, and orbital motions of globular clusters to the properties of the progenitor galaxies in which they formed, more than 10 billion years ago. By applying these insights to groups of globular clusters in the Milky Way, they could not only determine how many stars these progenitor galaxies contained, but also when they merged into the Milky Way.

"'The main challenge of connecting the properties of globular clusters to the merger history of their host galaxy has always been that galaxy assembly is an extremely messy process, during which the orbits of the globular clusters are completely reshuffled," Kruijssen explains.

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"By applying the neural network to these groups of globular clusters, the researchers could not only predict the stellar masses and merger times of the progenitor galaxies to high precision, but it also revealed a previously unknown collision between the Milky Way and an enigmatic galaxy, which the researchers named "Kraken."

"The collision with Kraken must have been the most significant merger the Milky Way ever experienced," Kruijssen adds. "Before, it was thought that a collision with the Gaia-Enceladus-Sausage galaxy, which took place some 9 billion years ago, was the biggest 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 truly transformed what the Milky Way looked like at the time."

"Taken together, these findings allowed the team of researchers to reconstruct the first complete merger tree of our Galaxy. Over the course of its history, the Milky Way 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 6 and 11 billion years ago."

Comment: The Milky Way was carefully designed, as noted before, to create a galaxy big enough to hide out the Earth in a safe spot for life to survive.