Using Euclid images and an AI image‑analysis tool, researchers examined about one million galaxies and found that AGN are significantly more common in merging systems. Early, dusty mergers show the strongest effect (about six times more AGN), while late‑stage mergers still show roughly double the AGN frequency. The study suggests mergers are the primary—and for the brightest AGN likely the only—mechanism capable of delivering the gas needed to power the most luminous black hole eruptions.
Galaxy Collisions Ignite Supermassive Black Holes — Euclid and AI Reveal the Link
A compilation of images of distant galaxies, some merging, some not, taken by Euclid. . | Credit: Euclid Collaboration
Scientists using data from the European Space Agency's Euclid mission, together with a new AI image‑analysis tool, have found strong observational evidence that major galaxy mergers trigger powerful eruptions from supermassive black holes at galactic centers.
Euclid and AI: A New Census of Active Galaxies
Launched in 2023, the Euclid space telescope combines a 1.2‑metre primary mirror, a 600‑megapixel camera and a wide field of view to image vast swaths of sky with high resolution. By examining a subset of roughly one million galaxies from Euclid's survey, researchers were able to compile the largest uniform census to date of galaxies hosting active galactic nuclei (AGN).
What Is an AGN—and How Do Mergers Turn Them On?
An AGN occurs when a supermassive black hole at a galaxy's core accretes large amounts of gas and dust. The inflowing material forms a bright accretion disk; magnetic fields and extreme conditions can launch relativistic jets. When such jets point toward Earth, we may observe a quasar or, in the most extreme aligned cases, a blazar.
Key Findings
Researchers separated the sample into galaxies showing evidence of a merger and those that appear non‑merging, then applied an AI image‑decomposition tool developed by Berta Margalef‑Bentabol and Lingyu Wang (SRON) to identify AGN and estimate their luminosities.
"This new approach can even reveal faint AGN that other identification methods will miss," said Margalef‑Bentabol.
The analysis shows that AGN are 2–6 times more common in merging galaxies than in non‑merging systems. The effect is strongest in early, dusty merger stages—where the galactic nucleus is obscured and detectable mainly in the infrared—showing about six times more AGN. In late‑stage mergers, where dust has settled and the system appears more regular, AGN remain roughly twice as common compared with non‑mergers.
Implications for Galaxy Evolution
These observations strongly support the idea that mergers funnel gas into galactic centers and are the principal trigger of AGN activity. The authors argue mergers are likely the primary—and for the most luminous AGN, probably the only—mechanism that can deliver enough material to fuelling the brightest black hole outbursts. Because AGN radiation can heat molecular gas and suppress star formation, linking AGN to mergers is important for models of galaxy growth and evolution.
Publication and Data
The results will appear in Astronomy & Astrophysics and are available as two preprints: one on the analysis connecting merging galaxies and AGN, and another describing the AI image‑decomposition tool.
