Euclid telescope shows merging galaxies are prime triggers for black hole outbursts

Space.com reports new findings from the Euclid space telescope showing that galaxy mergers play a major role in activating supermassive black holes.

The study used an artificial intelligence tool to examine one million galaxies observed by Euclid. Researchers aimed to understand when and why a galaxy develops an active galactic nucleus (AGN), which happens when the central black hole begins to draw in large amounts of gas.

The AI method allowed scientists to identify AGN that might be missed by other techniques.

As researcher Berta Margalef-Bentabol explained,

“This new approach can even reveal faint AGN that other identification methods will miss.”

By comparing galaxies that are merging with those that are not, the team found clear differences in the number of active black holes. Early-stage mergers with heavy dust showed six times more AGN, while later-stage mergers still showed twice as many as non-merging systems.

The results support the idea that mergers push gas toward the center of galaxies, which activates the black hole. Researcher Antonio La Marca said,

“We also conclude that mergers are very likely to be the only mechanism capable of feeding the most luminous AGN.”

These findings help scientists model how galaxies evolve over time.

How did the study connect mergers and AGN activity?

The Euclid team separated one million galaxies into two groups: those with visible signs of merging and those without. Using their AI tool, the researchers measured how many galaxies in each group hosted an active galactic nucleus.

According to Margalef-Bentabol, “This new approach allowed us to evaluate AGN in a uniform way across a very large sample.”

The results showed a clear pattern. Galaxies in the early stages of a merger, where dust still hides much of the nucleus, had six times more AGN detected in infrared light.

Galaxies in later merger stages, where dust has settled, still had double the number of AGN compared to non-merging galaxies. La Marca noted that “many AGN found in non-mergers may actually be in galaxies that already completed the chaotic stages of a merger.”

This suggests that the outward appearance of a calm galaxy does not always reveal its history. The study strengthens the link between mergers and black hole activity by offering a consistent measurement method across a large data set.

Why does this matter for galaxy evolution?

AGN represent a period of rapid growth for supermassive black holes. When a black hole draws in gas, the radiation released can heat and disrupt the surrounding material.

This affects the galaxy’s long-term ability to form stars. Because of this, knowing what activates AGN is important for understanding how galaxies change over time.

Euclid’s wide field of view made it possible to observe a large sample of galaxies across vast distances. Previous telescopes could detect distant AGN but could not capture enough galaxies at once to confirm how mergers relate to black hole activity.

Euclid now provides both image clarity and coverage to support statistical analysis.

La Marca stated that the evidence points toward mergers as the main trigger for powerful AGN, saying, “At the very least, they are the primary trigger.” This helps researchers model how gas moves through galaxies and how black holes grow through cosmic history.

The study also shows how AI tools can process large survey images. By identifying faint or hidden AGN, the method expands the types of galaxies that can be studied.

These insights will help scientists build a more complete picture of galaxy development as Euclid continues its mission.

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