Recent computational modeling indicates a tumultuous cosmic encounter approximately 11 billion years in the past profoundly reconfigured our home galaxy, precipitating a surge in stellar creation.
This visual representation, captured by the Gemini North telescope, depicts two spiral galaxies engaged in an interaction: NGC 4568 positioned below and NGC 4567 above. The image attribution is: International Gemini Observatory / NOIRLab / NSF / AURA / T.A. Rector, University of Alaska Anchorage & NSF’s NOIRLab / J. Miller, Gemini Observatory & NSF’s NOIRLab / M. Zamani, NSF’s NOIRLab / D. de Martin, NSF’s NOIRLab.
The Milky Way’s galactic disk, a vast, rotational expanse of stars and interstellar matter, possesses a form reminiscent of a celestial frisbee, with luminous spiral arms extending outwards from its core.
The predominant constellation of stellar bodies within our galaxy, including our own Sun, is situated within this disk structure, which traverses the cosmos at velocities surpassing 220 kilometers per second.
For numerous decades, astrophysicists have been endeavoring to ascertain the precise epoch of this expansive, revolving structure’s initial genesis.
“A pivotal indicator lies in the kinematic behavior and chronological assessment of celestial bodies: at a certain juncture in the galaxy’s formative period, stars began exhibiting synchronized, rotational motion, signifying what experts term the galaxy’s rotational acceleration phase,” stated Dr. Matthew Orkney from the University of Barcelona and the Institute of Space Studies of Catalonia, alongside Dr. Chervin Laporte of CNRS.
“Nevertheless, the formation of the Milky Way Galaxy did not occur in isolation.”
“For many years, the scientific community has posited that a violent confrontation with a smaller galactic entity played a significant role in sculpting the Milky Way as it is presently observed.”
“This hypothesis was substantiated in 2018, when data acquired from the European Space Agency’s Gaia mission unveiled a substantial population of stars whose aberrant movements could exclusively be attributed to a colossal merger event that transpired approximately 10 billion years ago.”
“This significant event is now globally recognized as the Gaia-Sausage-Enceladus (GSE) merger.”
To investigate the emergence and developmental trajectory of rotating galactic disks, Dr. Orkney and Dr. Laporte initiated sophisticated simulations of galaxies paralleling the Milky Way under a spectrum of cosmic circumstances.
These simulated environments afforded the investigators the capacity to scrutinize the reactions of galaxies akin to our own following ancient encounters with lesser celestial companions.
Their findings indicated that rotating stellar disks may have materialized considerably earlier in a galaxy’s evolutionary timeline than was previously theorized by astronomers.
However, the simulations also demonstrated that substantial galactic collisions possess the capability to severely destabilize, or even entirely annihilate, such disks.
Consequently, the point at which the Milky Way’s disk appears to achieve stable rotation might not signify the disk’s inception.
Rather, it could denote the period during which our Galaxy underwent reconstruction and recovery subsequent to a cataclysmic merger.
Leveraging insights gleaned from these simulations, the research team deduced that the Milky Way’s collision with the GSE galaxy most likely occurred around 11 billion years ago, predating many prior estimations.
Crucially, this proposed temporal framework harmonizes with a pronounced escalation in the formation of star clusters observed within the Milky Way.
Such effusions of stellar genesis are a natural consequence of galactic collisions, as the impact forces compress immense nebulae of gas, thereby instigating vigorous cycles of star production.
“The theoretical models for the GSE merger posit that a spectacular cosmic display should have ensued post-impact, augmenting star formation and facilitating the genesis of globular clusters. This represents the inaugural establishment of this correlative link,” remarked Dr. Laporte.
“This investigation underscores the profound interrelationship between galactic architecture and ancient collisions, which necessitates unified comprehension to fully elucidate our Galaxy’s historical narrative,” Dr. Orkney added.
The research outcomes have been disseminated in the Monthly Notices of the Royal Astronomical Society.
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Matthew D.A. Orkney & Chervin F.P. Laporte. 2026. Build-up and survival of the disc: from numerical models of galaxy formation to the Milky Way. MNRAS 548 (4): staf2154; doi: 10.1093/mnras/staf2154
