IceCube neutrinos give us first glimpse into the inner depths of an active galaxy
For the first time, an international team of scientists have found evidence of high-energy neutrino emission from NGC 1068, also known as Messier 77, an active galaxy in the constellation Cetus and one of the most familiar and well-studied galaxies to date. First spotted in 1780, this galaxy, located 47 million light-years away from us, can be observed with large binoculars. The results were published in Science, and shared in an online scientific webinar that gathered experts, journalists, and scientists from around the globe.
The IceCube Neutrino Observatory reported the first observation of a high-energy astrophysical neutrino source in 2018. The source, TXS 0506+056, is a known blazar located off the left shoulder of the Orion constellation and 4 billion light-years away.
“One neutrino can single out a source. But only an observation with multiple neutrinos will reveal the obscured core of the most energetic cosmic objects,” says Francis Halzen, a professor of physics at the University of Wisconsin–Madison and principal investigator of IceCube. He adds, “IceCube has accumulated some 80 neutrinos of teraelectronvolt energy from NGC 1068, which are not yet enough to answer all our questions, but they definitely are the next big step towards the realization of neutrino astronomy.”
Unlike light, neutrinos can escape in large numbers from extremely dense environments in the universe and reach Earth largely undisturbed by matter and the electromagnetic fields that permeate extragalactic space. Although scientists envisioned neutrino astronomy more than 60 years ago, the weak interaction of neutrinos with matter and radiation makes their detection extremely difficult. Neutrinos could be key to our queries about the workings of the most extreme objects in the cosmos.
NGC 1068 is an active galaxy—a Seyfert II type in particular—seen from Earth at an angle that obscures its central region where the black hole is located. In a Seyfert II galaxy, a torus of nuclear dust obscuresmost of the high-energy radiation produced by the dense mass of gas and particles that slowly spiral inward toward the center of the galaxy.
“Recent models of the black hole environments in these objects suggest that gas, dust, and radiation should block the gamma rays that would otherwise accompany the neutrinos,” says Hans Niederhausen, a postdoctoral associate at Michigan State University. “This neutrino detection from the core of NGC 1068 will improve our understanding of the environments around supermassive black holes.”
NGC 1068 could become a standard candle for future neutrino telescopes, according to Theo Glauch, a postdoctoral associate at the Technical University of Munich (TUM), in Germany.
“It is already a very well-studied object for astronomers, and neutrinos will allow us to see this galaxy in a totally different way. A new view will certainly bring new insights,” says Glauch.With the neutrino measurements of TXS 0506+056 and NGC 1068, IceCube is one step closer to answering the century-old question of the origin of cosmic rays. Additionally, these results imply that there may be many more similar objects in the universe yet to be identified. “The unveiling of the obscured universe has just started, and neutrinos are set to lead a new era of discovery in astronomy,” says Elisa Resconi, a professor of physics at TUM.
“It is great news for the future of our field,” says Marek Kowalski, an IceCube collaborator and senior scientist at Deutsches Elektronen-Synchrotron, in Germany. “It means that with a new generation of more sensitive detectors there will be much to discover. The future IceCube-Gen2 observatory could not only detect many more of these extreme particle accelerators but would also allow their study at even higher energies. It’s as if IceCube handed us a map to a treasure trove.”
- IceCube news: https://icecube.wisc.edu/news/press-releases/2022/11/icecube-neutrinos-give-us-first-glimpse-into-the-inner-depths-of-an-active-galaxy/
- “Evidence for neutrino emission from the nearby active galaxy NGC 1068,” The IceCube Collaboration: R. Abbasi et al., Science 378, 6619 (2022), DOI:10.1126/science.abg3395 / arXiv:2211.09972
- Webinar here, with presentation slides here