When Galaxies Collide: Euclid Reveals What Triggers Active Black Holes

Using early data from the European Space Agency's Euclid space telescope, astronomers have analyzed over one million galaxies to test a long-standing idea in astrophysics: that galaxy mergers help trigger the growth of supermassive black holes. In this SETI Live, host Dr. Moiya McTier will explore two new Euclid studies that combine vast sky surveys, machine learning, and multi-wavelength observations to uncover when and why active galactic nuclei (AGN) ignite. The results show that galaxies in the midst of mergers are far more likely to host actively feeding black holes — and that the brightest AGN are almost always found in cosmic collisions. Dr. McTier will be joined by lead authors Dr. Berta Margalef-Bentabol, Dr. Lingyu Wang, and Dr. Antonio la Marca from the Space Research Organisation Netherlands (SRON). They will discuss how Euclid identifies merging galaxies at scale, how researchers measure the black hole's contribution to a galaxy's light, and what this tells us about the coevolution of galaxies and their central black holes. We'll also look ahead to what future Euclid data could reveal as the survey expands to billions of galaxies. (Recorded live 15 January 2026.)