Buried beneath the Antarctic ice, a collection of detectors known as the IceCube Neutrino Observatory has detected an unusual signal from galaxy NGC 1068. This galaxy, also referred to as the Squid Galaxy, emits strong neutrinos but weak gamma rays, presenting a scientific puzzle.
Theoretical physicists from UCLA and universities in Osaka and Tokyo have observed this phenomenon and proposed a new theory on neutrino production. Their findings suggest that helium nuclei collide with ultraviolet photons in the galaxy’s central region. This collision fragments the nuclei, releasing neutrons that decay into neutrinos without producing gamma rays.
Alexander Kusenko, professor of physics and astronomy at UCLA and senior fellow at Kavli IPMU, explained: “We have telescopes that use light to look at stars, but many of these astrophysical systems also emit neutrinos. To see neutrinos, we need a different type of telescope, and that’s the telescope we have at the South Pole.”
The IceCube telescope recorded energetic neutrinos accompanied by weak gamma-ray emissions from NGC 1068. Typically, energetic neutrinos are associated with strong gamma rays due to interactions between protons and photons. However, this is not observed in NGC 1068.
A paper published in Physical Review Letters suggests high-energy neutrinos result from neutron decay when helium nuclei break apart under ultraviolet radiation. These interactions produce electrons that generate gamma rays consistent with observations.
Koichiro Yasuda of UCLA noted: “Hydrogen only has a proton… But neutrons have an additional way of forming neutrinos that don’t produce gamma rays.” The study uncovers hidden astrophysical sources previously unnoticed due to faint gamma-ray signatures.
Yoshiyuki Inoue from Osaka University stated: “NGC 1068 is just one of many similar galaxies… Future detections will help test our theory.” The research holds implications for understanding supermassive black holes like those at our galaxy’s center.
Kusenko emphasized the potential technological impacts: “Investment in science is going to produce something… big decades later.” The work was supported by various scientific bodies including the Department of Energy and Japan Society for Promotion of Science.
