In 2022, the IceCube Neutrino Observatory at the South Pole announced evidence for high-energy neutrinos spewing from the “nearby” active galaxy NGC 1068. One of the brightest X-ray sources in the universe, NGC 1068 is an active galactic nucleus (AGN) with a central, supermassive black hole that actively gobbles up surrounding matter.
X-rays shine brightly in the immediate surroundings of the supermassive black hole that powers NGC 1068. At the same time, gamma rays, which are typically used as a guide in IceCube’s searches for neutrino sources, are not detected at comparable levels with neutrinos in this source. In AGNs like NGC 1068, X-rays can escape the dense environment around the supermassive black hole and provide information about its properties while gamma rays are absorbed. Neutrinos could also form if particles are accelerated and subsequently interact with the X-rays in this environment.
Using 13 years of IceCube data, the IceCube Collaboration did a follow-up search for additional X-ray-emitting galaxies as a source of high-energy neutrinos. The study had two key findings: NGC 1068 remains the most significant neutrino source in the northern sky, and a population of newly selected galaxies revealed evidence for neutrino emission from similar sources. These results are presented in a paper submitted to The Astrophysical Journal Letters.
“The NGC 1068 observation marked one of the few times we’d seen such a clear neutrino signal from a galaxy powered by a black hole,” says Tomas Kontrimas, who was a PhD student at Technische Universität München (TUM) when he contributed to the work. “But it also raised an important question: is NGC 1068 unique, or just the first of many galaxies capable of producing neutrinos?”
The researchers focused on the northern part of the sky where neutrinos travel through the Earth before arriving at IceCube. The Earth acts as a natural shield, blocking most background cosmic rays and, therefore, providing a clean view of neutrinos arriving from space. Similar to a 2024 study, they looked at X-ray-emitting active galaxies that could also be linked to high-energy neutrino production.
“To improve on previous work, we focused on galaxies that were emitting “hard” X-rays in the 20–50 kiloelectronvolt range, which can penetrate the dense gas and dust that often obscure a galaxy’s core,” explains Chiara Bellenghi, TUM postdoctoral researcher and study lead. “Using these criteria, we selected 47 X-ray–bright AGNs from the Swift/BAT Spectroscopic Survey (excluding NGC 1068) and tested each one as well as the whole group for neutrino emission.”
They observed an excess of neutrino emission from the selected population with a statistical significance above the 3σ threshold.
“This new evidence suggests that NGC 1068 is not an isolated case, but rather part of a broader class of active galaxies that produce high-energy neutrinos,” says Elena Manao, a PhD student at TUM who contributed to the work. “This is a significant step toward identifying one of the population of sources responsible for the cosmic neutrinos detected on Earth.”
The IceCube Collaboration is not stopping here, however, as some of the most promising nearby X-ray–bright AGNs lie in the southern sky, where they face more background noise but also hold discovery opportunities. Future improvements in data processing and detector calibration will no doubt boost IceCube’s sensitivity in that area.
These efforts will help better understand the mechanisms that generate neutrinos in the extreme environments around supermassive black holes, bringing them closer to revealing how the universe’s most energetic particles are produced and accelerated.
+ info “Evidence for Neutrino Emission from X-ray Bright Active Galactic Nuclei with IceCube,” IceCube Collaboration: R. Abbasi et al. Submitted to The Astrophysical Journal Letters. arxiv.org/abs/2510.13403