Gravitational waves (GWs) are produced by some of the most violent and energetic astrophysical phenomena, such as black holes and neutron star mergers. They have long been suspected of being astrophysical sources of neutrinos, ghostlike cosmic messengers hurtling through space unimpeded. Thus far, common astrophysical sources of neutrinos and photons have been identified, as have common sources of GWs and light. However, common sources of both GWs and high-energy neutrinos have yet to be confirmed.
In a study published in The Astrophysical Journal, the IceCube Collaboration and the LIGO-Virgo-KAGRA Collaboration presented an extended search to find joint detection of GWs and high-energy neutrinos. No significant joint sources were found, and upper limits on the rate density of the common sources of GWs and high-energy neutrino sources were reported.
The study leveraged data collected from the IceCube neutrino detector situated at the South Pole as well as data from the third observing run of the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo gravitational wave detectors. Although previous analyses looked solely at confident GW events, the researchers also included low-confidence, or subthreshold, GW events for this analysis.
“Finding such a joint detection from a low-confidence GW event would increase the confidence of that GW event being an actual astrophysical signal,” explains Doğa Veske, assistant professor at Middle East Technical University and colead on the study.
Veske and collaborators used the Low Latency Algorithm for Multi-messenger Astrophysics (LLAMA) pipeline to analyze confident and low-confidence GW events. For every GW event, they collected the neutrino triggers for around 500 seconds and estimated the likelihood that these neutrinos came from the same source as the GW event. Then, those values were compared to a set of known values from previously simulated independent GW and neutrino detections.
Researchers also analyzed the whole set at once to assess whether there were several weak coincidences that may not be found individually but might stand out when analyzed together.
“For beamed emissions and low neutrino emission energies, the upper limits restrict the presence of such sources for isotropic neutrino emissions with high luminosities,” says Veske. “The levels of the upper limits also reinforce the need to improve the detectors in order to reliably observe fainter emissions.”
With more data incoming, new IceCube searches for joint sources of GW events and high-energy neutrinos are foreseeable. Follow-up analyses using the LLAMA pipeline were conducted in real time during the fourth observing run of the LIGO, Virgo, and KAGRA (LVK) detectors, which ended in late 2025. Results were immediately shared with the multimessenger astronomy community to prompt additional observations. The LLAMA team is looking forward to the restart of operations of the LVK gravitational-wave detector network, expected this fall.
“We are developing more powerful statistical methods to get the most out of the data,” says Zsuzsa Márka, an associate research scientist at Columbia University and colead on the study. “With the enhanced capabilities of the next-generation IceCube-Gen2 detector and future GW detectors, we are poised for more searches and multimessenger detections of these sources.”
+ info “Deep Search for Joint Sources of Gravitational Waves and High-Energy Neutrinos with IceCube During the Third Observing Run of LIGO and Virgo,” IceCube Collaboration: R. Abbasi et al. Published in The Astrophysical Journal 1003 (2026) 41, iopscience.iop.org, arXiv