NGC 1068, often known as Messier 77, is an active galaxy in the constellation Cetus that has been one of the most well-known and extensively researched galaxies to date. An international team of researchers has discovered evidence of high-energy neutrino emission from this galaxy for the first time.
This galaxy, which is 47 million light-years from Earth and was first discovered in 1780, can be seen with powerful binoculars. The findings were presented today in an online scientific webinar attended by professionals, journalists, and scientists from all across the world. The findings will be published tomorrow (Nov. 4, 2022) in Science.
The discovery was made at the IceCube Neutrino Observatory, a giant neutrino observatory financed by the National Science Foundation that spans 1 billion tons of instrumented ice 1.5 to 2.5 kilometers below the surface of Antarctica near the South Pole.
2018 saw the publication of the first detection of a high-energy astrophysical neutrino source by this singular observatory, which uses neutrinos to probe the furthest reaches of our cosmos. The source, TXS 0506+056, is a well-known blazar that is 4 billion light-years away and situated off the left shoulder of the Orion constellation.
“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 may escape from the universe’s most dense surroundings in vast quantities, and they can do so while mostly avoiding interference from matter and the electromagnetic fields that permeate interstellar space.
It is great news for the future of our field. 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.
Marek Kowalski
Although neutrino astronomy has been envisioned by scientists for more than 60 years, it is extremely challenging to detect neutrinos due to their weak interaction with matter and radiation. Our questions regarding the operation of the most extreme objects in the cosmos may be best answered by neutrinos.
“Answering these far-reaching questions about the universe that we live in is a primary focus of the U.S. National Science Foundation,” says Denise Caldwell, director of NSF’s Physics Division.
As is the case with our home galaxy, the Milky Way, NGC 1068 is a barred spiral galaxy, with loosely wound arms and a relatively small central bulge. However, unlike the Milky Way, NGC 1068 is an active galaxy where most radiation is not produced by stars but due to material falling into a black hole millions of times more massive than our Sun and even more massive than the inactive black hole in the center of our galaxy.
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 obscures most 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 and one of the main analyzers of the paper. “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, and another main analyzer.
“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.
These findings represent a significant improvement on a prior study on NGC 1068 published in 2020, according to Ignacio Taboada, a physics professor at the Georgia Institute of Technology and the spokesperson of the IceCube Collaboration.
“Part of this improvement came from enhanced techniques and part from a careful update of the detector calibration,” says Taboada. “Work by the detector operations and calibrations teams enabled better neutrino directional reconstructions to precisely pinpoint NGC 1068 and enable this observation. Resolving this source was made possible through enhanced techniques and refined calibrations, an outcome of the IceCube Collaboration’s hard work.”
The improved analysis points the way toward superior neutrino observatories that are already in the works.
“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.”
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 and another main analyzer.
“Several years ago, NSF initiated an ambitious project to expand our understanding of the universe by combining established capabilities in optical and radio astronomy with new abilities to detect and measure phenomena like neutrinos and gravitational waves,” says Caldwell.
“The IceCube Neutrino Observatory’s identification of a neighboring galaxy as a cosmic source of neutrinos is just the beginning of this new and exciting field that promises insights into the undiscovered power of massive black holes and other fundamental properties of the universe.”
