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Researchers discover that the more gas is dragged in galactic collisions, the faster the Milky Way disk was reset 11 billion years ago.
The study was published in the Monthly Notices of the Royal Astronomical Society in May 2026 by astrophysicists Matthew Orkney and Chervin Laporte.
Therefore, the Gaia-Sausage-Enceladus (GSE) collision destroyed the pre-existing stellar disk of the Milky Way and forced the complete reconstruction of the galaxy.
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The research cross-referenced data from the European Space Agency’s Gaia space telescope with cosmological simulations called Auriga.
According to the study, the current thin disk of the Milky Way began to form only 2 billion years after the Big Bang.
The Big Bang occurred 13.8 billion years ago, according to NASA, which places the original disk in formation 11.8 billion years ago.
Matthew Orkney from the University of Barcelona discovered the hidden mechanism
Matthew Orkney is an astrophysicist at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB).
Orkney has been working in partnership with the Institut d’Estudis Espacials de Catalunya (IEEC) since 2022.
According to the researcher, the galaxy’s thin disk contains 100 billion stars distributed in a flattened structure 100,000 light-years in diameter.
Therefore, the work used 4 million stars mapped by Gaia over 8 years of continuous observation between 2014 and 2022.
Additionally, the study applied the Auriga simulations, created in 2017 by an international consortium led by the Max Planck Institute for Astrophysics in Garching, Germany.
How the gas stripping mechanism reset an entire disk
Gas stripping is the process by which interstellar gas is dragged out of a galaxy during a collision with another.
According to the Royal Astronomical Society article, the GSE had about one-fifth of the mass of our current galaxy.
Therefore, the collision displaced approximately 10 billion solar masses of molecular gas from the original disk.
The removed gas formed new structures on the galaxy’s periphery in star burst cycles that lasted for 2 billion years after the impact.
According to the Auriga simulations, the mechanism is universal and occurs in all galaxies of similar size to the galactic system.
Additionally, the study identified a direct correlation between the amount of gas dragged and the time required for the disk to reconstitute.
Chervin Laporte from CNRS detailed the simulations that validated the thesis
Chervin Laporte is a researcher at the French National Center for Scientific Research (CNRS) based in Marseille.
Laporte conducted the 12 Auriga cosmological simulations used in the study between 2023 and 2026.
Each simulation took 8 months of processing on the SuperMUC-NG supercomputer at the Leibniz Computing Center in Munich.
The German supercomputer has a capacity of 26.9 petaflops and is the 13th most powerful in the world, according to the TOP500 ranking of June 2025.
According to the team, each simulation reproduced 13.8 billion years of cosmic evolution using 1 trillion virtual particles.
The Gaia telescope: 1.8 billion stars mapped in 8 years
The Gaia space telescope was launched on December 19, 2013, by the European Space Agency.
According to the ESA, the equipment mapped 1.8 billion stars in 8 years of operation.
Therefore, the mission records the position, velocity, and brightness of each star with a precision of 24 microarcseconds.
This is equivalent to measuring the thickness of a hair at 1,000 km away, according to the ESA.
According to the ESA, the Gaia telescope was deactivated in January 2025 after exhausting maneuvering fuel.
Additionally, the 1.8 billion stars mapped represent only 1.5% of the estimated 200 billion stars in the host galaxy.
The Max Planck Institute and the Auriga Collaboration
The Max Planck Institute for Astrophysics in Garching has coordinated the Auriga collaboration since 2017.
The consortium brings together universities in 6 countries: Germany, the United Kingdom, France, Spain, the United States, and the Netherlands.
According to Max Planck, the Auriga simulations have already produced more than 90 scientific articles published in astrophysics journals.
Therefore, it is the largest cosmological galaxy simulation project currently in operation in the world.
- Auriga (Max Planck): 1 trillion particles, 12 simulations, SuperMUC-NG, created in 2017
- Illustris TNG (Harvard/MIT): 18 billion particles, supercomputer Hazel Hen, created in 2018
- EAGLE (Durham): 6.8 billion particles, COSMA-7, created in 2015
- FIRE-2 (Caltech): 3 billion particles, Stampede2, created in 2018
- Romulus (Yale): 1.8 billion particles, Bridges-2, created in 2017
According to ICCUB, the thin disk of our galaxy currently concentrates 95% of the stars observable from Earth, including the Sun and the solar system.
For comparison with other astrophysical discoveries, see coverage on SpaceX and Google’s orbital data centers and the Tengeh solar park in Singapore.
According to the American Astronomical Society, the study by Orkney and Laporte resolves a 15-year controversy over the age of the Milky Way’s thin disk.
Previous estimates ranged from 6 to 12 billion years for the age of the disk, according to a revised analysis by the Astrophysical Journal in 2024.
Therefore, Orkney’s result places the Milky Way among the oldest spiral galaxies with a preserved disk in the known universe.
Additionally, data from the James Webb telescope showed in 2023 that galaxies with thin disks existed up to 1 billion years after the Big Bang.
According to researcher Carlos Frenk from the University of Durham, UK, Orkney’s finding “changes the way we understand the evolution of spiral-type galaxies over the last 13 billion years.”
Frenk leads the EAGLE Simulations collaboration, a direct competitor to Auriga in international cosmological research.
According to Frenk, three independent simulations from the EAGLE Project have already confirmed the gas stripping mechanism in galaxies similar to the Milky Way.
Therefore, the international astrophysical community considers the topic closed: thin disks survive most collisions but need to rebuild via subsequent star bursts.
Why the Milky Way disk may collide again in 4 billion years
The Andromeda galaxy (M31) is 2.5 million light-years from the spiral galaxy and is approaching at 400,000 km/h.
The direct impact is predicted to occur in 4 billion years, according to NASA calculations.
Therefore, the merger between the two galaxies is expected to repeat the gas stripping process described by Orkney and Laporte.
According to the study, the current thin disk of the galactic system may be partially or completely destroyed by the second galactic encounter in its history.
According to the team, the merger will produce a new giant elliptical galaxy provisionally named Milkomeda by the international collaboration.
The discovery by Orkney and Laporte establishes that galactic collisions are a natural part of the evolution of thin disks in the universe.
However, the study was unable to identify the exact origin of the Gaia-Sausage-Enceladus galaxy, which completely fragmented after the impact.
However, according to the Royal Astronomical Society, new data from the James Webb Space Telescope may help trace remnants of the GSE in research scheduled for 2027.
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