Groundbreaking simulation reveals that a cataclysmic collision 11 billion years ago transformed our galaxy and sparked an explosion of star formation.
The Gemini North telescope captured this stunning image of interacting spiral galaxies, NGC 4568 (bottom) and NGC 4567 (top). Image credits: International Gemini Observatory / NOIRLab / NSF / AURA / TA Chancellor, University of Alaska Anchorage and NSF’s NOIRLab / J. Miller, Gemini Observatory and NSF’s NOIRLab / M. Zamani, NSF’s NOIRLab / D. de Martin, NSF’s NOIRLab.
The Milky Way’s disk is an extensive, rotating structure shaped like a cosmic pancake, featuring luminous spiral arms extending outward from its core.
Most stars in our galaxy, including our Sun, reside within this disk, which rotates at speeds exceeding 220 kilometers per second.
For decades, astronomers have sought to pinpoint the origins of this immense rotating structure.
“Key insights lie in the motion and age of the stars. At some stage in the galaxy’s early history, stars began moving in a consistent rotational pattern, which scientists term the galaxy’s ‘spin-up’ time,” explained Dr. Matthew Orkney from the University of Barcelona and Catalunya Space Institute, along with Dr. Chervin Laporte from CNRS.
“However, the Milky Way did not form in isolation.”
“For years, researchers have theorized that violent collisions with smaller galaxies significantly contributed to the formation of our present-day Milky Way.”
This hypothesis gained traction in 2018, when data from ESA’s Gaia mission unveiled a substantial population of stars whose unusual motions could only be attributed to a gigantic merger approximately 10 billion years ago.”
“This event is now referred to as the Gaia Sausage Enceladus (GSE) merger.”
To better understand how rotating galactic disks develop and evolve, Orkney and Laporte conducted simulations of galaxies akin to the Milky Way under various cosmic scenarios.
Their model allowed them to examine how galaxies like ours would react to ancient collisions with smaller companion galaxies.
They discovered that the rotating stellar disk may have formed much earlier in the galaxy’s timeline than previously believed.
However, the simulations also indicated that large-scale galactic collisions could significantly disrupt, or completely annihilate, these disks.
This suggests that the transition of the Milky Way’s disk into a stable rotation may not mark the moment of its birth but rather a phase of rebuilding following a catastrophic merger.
From their simulations, the researchers posited that the collision between the Milky Way and the GSE galaxy likely occurred around 11 billion years ago, earlier than many earlier estimates.
This proposed timeframe aligns with a remarkable surge in star cluster formation within the Milky Way.
These bursts of star birth are a natural aftermath of galactic collisions, compressing vast clouds of gas and igniting monumental waves of star formation.
“GSE merger models indicate that galactic fireworks were expected post-collision, enhancing star formation, and promoting the emergence of globular clusters. This is the first instance of this connection being demonstrated,” said Dr. Laporte.
“This research underscores critical relationships between galactic structure and ancient collisions, which must be considered holistically to grasp the history of galaxies,” added Dr. Orkney.
For more details on these findings, refer to the Royal Astronomical Society Monthly Notices.
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Matthew DA Orkney & Chervin FP Laporte. 2026. Disk formation and survival: From numerical models of galaxy formation to the Milky Way. MNRAS 548 (4): staf2154; doi: 10.1093/mnras/staf2154
Source: www.sci.news
