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<\/p>\nNew simulations suggest a violent collision 11 billion years ago reshaped our Galaxy and triggered a burst of star formation.<\/p>\n
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This image from the Gemini North telescope shows a pair of interacting spiral galaxies: NGC 4568 (bottom) and NGC 4567 (top). Image credit: International Gemini Observatory \/ NOIRLab \/ NSF \/ AURA \/ T.A. Rector, University of Alaska Anchorage & NSF\u2019s NOIRLab \/ J. Miller, Gemini Observatory & NSF\u2019s NOIRLab \/ M. Zamani, NSF\u2019s NOIRLab \/ D. de Martin, NSF\u2019s NOIRLab.<\/p>\n
The Milky Way\u2019s disk is a sprawling, rotating structure of stars and gas shaped somewhat like a cosmic pancake, with bright spiral arms extending outward from its center.<\/p>\n
Most of the Galaxy\u2019s stars \u2014 including the Sun \u2014 reside within this disk, which spins through space at speeds exceeding 220 km per second.<\/p>\n
For decades, astronomers have been trying to pinpoint when this vast rotating structure first emerged.<\/p>\n
\u201cA key clue lies in the motions and ages of the stars: at some point in the Galaxy\u2019s early history, the stars began moving in a coherent, rotating pattern, marking what scientists call the Galaxy\u2019s spin-up time,\u201d said Dr. Matthew Orkney from the University of Barcelona and the Institute of Space Studies of Catalonia and Dr. Chervin Laporte from CNRS.<\/p>\n
\u201cHowever, the Milky Way Galaxy did not form in isolation.\u201d<\/p>\n
\u201cFor decades, scientists have suspected that a violent collision with a smaller galaxy played an important role in shaping the Milky Way as we observe it today.\u201d<\/p>\n
\u201cThis suspicion was confirmed in 2018, when data from ESA\u2019s Gaia mission revealed a large population of stars whose unusual motions could only be explained by a massive merger that occurred about 10 billion years ago.\u201d<\/p>\n
\u201cThis event is now known as the Gaia-Sausage-Enceladus (GSE) merger<\/a>.\u201d<\/p>\n To explore how rotating galactic disks emerge and evolve, Dr. Orkney and Dr. Laporte ran simulations of galaxies similar to the Milky Way under a variety of cosmic scenarios.<\/p>\n The models allowed the authors to examine how galaxies like our own respond to ancient collisions with smaller companions.<\/p>\n They found that rotating stellar disks may have formed far earlier in a galaxy\u2019s history than astronomers once believed.<\/p>\n But the simulations also revealed that major galactic collisions can severely disrupt \u2014 or even completely destroy \u2014 those disks.<\/p>\n That means the point at which the Milky Way\u2019s disk appears to settle into a stable rotation may not represent the birth of the disk itself.<\/p>\n Instead, it could mark the period when our Galaxy rebuilt and recovered after a catastrophic merger.<\/p>\n Using clues from the simulations, the researchers concluded that the Milky Way\u2019s collision with the GSE galaxy likely took place around 11 billion years ago \u2014 earlier than many previous estimates<\/a> had suggested.<\/p>\n Importantly, this proposed timeline matches a dramatic rise in star cluster formation within the Milky Way.<\/p>\n Such bursts of stellar birth are a natural aftermath of galactic collisions, as the impacts compress vast clouds of gas and ignite intense waves of star formation.<\/p>\n \u201cModels of the GSE merger predict that a galactic firework should have followed the impact, raising star formation and fostering the formation of globular clusters. This is the first time this link has been made,\u201d Dr. Laporte said.<\/p>\n \u201cThis research highlights the important relationship between galactic structure and ancient collisions, which must be understood in unison in order to understand the history of our Galaxy,\u201d Dr. Orkney added.<\/p>\n