Which galaxies could a global neutrino network reveal next?

A galaxy can conceal its most energetic activity from gamma-ray telescopes while still releasing neutrinos. These particles escape environments that absorb high-energy light, potentially carrying information from close to a feeding supermassive black hole. But which galaxies should neutrino observatories watch next?

In a new preprint, Lena Saurenhaus, Francesca Capel and Foteini Oikonomou forecast searches for Seyfert galaxies, whose bright central regions are powered by matter accreting onto black holes. Their standout target is the Circinus Galaxy. Under specified assumptions about neutrino production and future detectors, it could reach the conventional five-sigma discovery threshold by 2038. That is a conditional forecast, not a detection announcement or guaranteed deadline.

A hidden source near the black hole

The study builds on evidence for neutrinos from the nearby Seyfert galaxy NGC 1068. Its neutrino signal, without accompanying TeV gamma-ray emission, motivates models in which the particles originate in a compact, obscuring environment.

The authors investigate the black hole’s corona: a hot, magnetized region associated with X-ray emission. In their model, magnetic turbulence accelerates protons. Interactions with surrounding gas and X-ray photons then produce neutrinos and gamma rays. Neutrinos escape, while high-energy gamma rays are absorbed and their energy is redistributed into lower-energy radiation, potentially observable at MeV energies.

The predicted neutrino output depends on intrinsic X-ray luminosity, magnetic turbulence and the pressure carried by energetic particles relative to the thermal gas. Crucially, the authors’ earlier population calculations found that making every Seyfert behave like NGC 1068 would overproduce the measured diffuse neutrino background. A few conspicuous sources need not represent the majority.

Forecasting a worldwide search

The proposed network combines IceCube in Antarctica, Baikal-GVD in Russia, KM3NeT/ARCA in the Mediterranean and the planned P-ONE observatory in the Pacific. Their different locations offer complementary access to the sky.

The researchers calculate expected signal and atmospheric-background events, incorporating reconstructed particle energies and arrival directions. They use an “Asimov” dataset—expected event counts rather than a particular random realization of observations—to estimate statistical significance. Independent observations from different detectors are combined through a joint likelihood.

These are simplified instrument forecasts. Because detailed public information is limited, the three water-based detectors receive IceCube-like effective areas adjusted for their locations. Their directional resolution is modeled using KM3NeT/ARCA projections. Assumed full-operation dates are 2028 for Baikal-GVD, 2030 for ARCA and 2036 for P-ONE; data already collected by partially built detectors are omitted.

Circinus stands apart

For individual-source searches, the team selects ten especially X-ray-bright Seyferts from the BASS catalog, excluding NGC 1068 and objects whose jets or multiple nuclei complicate the coronal interpretation.

Circinus leads the forecasts. Its proximity—4.2 megaparsecs—helps make its intrinsic X-ray flux particularly high. In the population’s lower-efficiency “average” scenario, Circinus reaches five sigma in 2038 and roughly six sigma in 2040. The 2038 forecast requires Seyferts to explain the diffuse astrophysical neutrino flux up to about 100 TeV and Circinus to be at least as efficient a neutrino emitter as the population average.

Most other targets remain difficult to identify individually. More optimistic emission assumptions give much earlier discoveries, but existing neutrino observations already suggest those assumptions overestimate some sources. Gamma-ray measurements and non-detections also restrict the brightest allowed predictions.

Adding galaxies, not just telescopes

The alternative is stacking: combining evidence from many known galaxy positions to search for their collective emission. The study considers 213 X-ray-selected Seyferts, excluding NGC 1068.

In the average scenario, the full network reaches five sigma in 2036. Yet Circinus contributes heavily to that result. Removing it pushes the projected threshold to 2046, with significance of about 3.8 sigma in 2040. A strong stacked signal therefore would not necessarily demonstrate that many galaxies contribute comparably.

Adding progressively fainter sources also brings diminishing returns. About 50 sources recover 99 percent of the full sample’s forecast significance in the average scenario when Circinus is included; roughly 100 are needed without it.

The practical message is to combine complementary observatories with carefully chosen targets. Future MeV gamma-ray observations could independently test the proposed coronal emission mechanism. Whether the predicted discoveries arrive depends on real detector performance, construction schedules and, most fundamentally, whether Seyfert coronae produce neutrinos as this model assumes.