Euclid Telescope Shows Merging Galaxies Trigger Black Hole Outbursts

New research from the Euclid space telescope shows that galaxy mergers play a crucial role in activating supermassive black holes, according to Space.com. Scientists used an artificial intelligence tool to analyze one million galaxies observed by Euclid to understand when and why a galaxy develops an active galactic nucleus (AGN)—a phenomenon that occurs when the central black hole begins accreting large amounts of gas.

The AI-based approach enabled researchers to detect AGN that might otherwise be overlooked. As researcher Berta Margalef-Bentabol explained, “This new approach can even reveal faint AGN that other identification methods will miss.”

By comparing merging galaxies to non-merging ones, the team identified significant differences in AGN activity. Early-stage mergers, still shrouded in dust, exhibited six times more AGN, while later-stage mergers showed double the number of active black holes compared to galaxies not undergoing mergers.

The findings support the theory that galaxy mergers drive gas toward the central black hole, triggering AGN activity. Researcher Antonio La Marca noted, “We also conclude that mergers are very likely to be the only mechanism capable of feeding the most luminous AGN.”

To conduct the study, Euclid researchers divided one million galaxies into two categories: those showing signs of merging and those appearing undisturbed. Using the AI tool, they uniformly evaluated the presence of AGN across the large sample. According to Margalef-Bentabol, “This new approach allowed us to evaluate AGN in a uniform way across a very large sample.”

The study revealed a consistent pattern: galaxies in the early stages of a merger, where dust obscures the nucleus, had six times more AGN detected in infrared light. Even in later stages, when dust has settled, the AGN count remained double that of non-merging galaxies. La Marca added, “Many AGN found in non-mergers may actually be in galaxies that already completed the chaotic stages of a merger.”

These results highlight that a galaxy’s calm appearance does not always reveal its past. By providing a large and uniform data set, the study reinforces the connection between mergers and black hole activity.

Understanding AGN activation is vital for modeling galaxy evolution. AGN represent rapid growth phases for supermassive black holes, and the radiation they emit can heat and disrupt surrounding material, affecting star formation in the galaxy over time.

Euclid’s wide field of view allowed astronomers to study a vast number of galaxies across large cosmic distances, surpassing previous telescopes that could detect distant AGN but lacked the coverage to establish statistical trends.

La Marca emphasized the significance of these findings, saying, “At the very least, they are the primary trigger.” The study also demonstrates the power of AI in analyzing large-scale astronomical surveys, revealing faint or hidden AGN and expanding the range of galaxies that can be examined.

These insights will help scientists create a more comprehensive understanding of galaxy evolution as Euclid continues its mission.