4 minute read
IceCube Neutrinos
by Lisa Potter
FOR THE FIRST TIME, AN INTERNATIONAL TEAM OF SCIENTISTS HAS FOUND EVIDENCE OF STEADY HIGHENERGY NEUTRINO EMISSION FROM A SOURCE BEYOND OUR SOLAR SYSTEM.
The neutrinos originate from NGC 1068, an active galaxy in the constellation Cetus. The detection was made at the IceCube Neutrino Observatory, a massive neutrino telescope embedded at depths of 1.5 to 2.5 kilometers into the ultrapure ice below Antarctica’s surface near the South Pole.
The University of Utah joined the IceCube Collaboration as a full institutional member in 2020. Carsten Rott, who holds the Jack W. Keuffel Memorial Chair at the U’s Department of Physics & Astronomy, has been with the IceCube Collaboration since the early construction phase of the observatory.
“After more than ten years of taking data, it is exciting to continue to see breakthroughs like this evidence for neutrino emission from NGC 1068 that bring us closer to understanding the origins of the energetic particles we observe in the universe,” Rott says.
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 makes their detection extremely difficult for today's scientists.
Neutrinos could be key to our queries about the workings of the most extreme objects in the cosmos.
A candidate extreme object is NGC 1068, a type 2 Seyfert active galaxy where most radiation is not produced by stars but is due to material falling into a black hole. Surrounding NGC 1068 is a torus of nuclear dust that 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 analyzer at Michigan State University. “This neutrino detection from the core of NGC 1068 will improve our understanding of the environments around supermassive black holes.”
With the neutrino measurements of 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. Shiqi Yu, recently hired at the U, is leading efforts to search IceCube’s data for neutrinos in the direction of other Seyfert II galaxies and if a general pattern can be established. “Advanced machine learning techniques are essential in helping us find more astrophysical neutrino signals with IceCube,” says Yu, “which can lead to better understanding of the astrophysical sources that produce them. The improved knowledge then can be used to find more similar sources.”
“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,” says NSF Physics Division Director Diana Caldwell.
A NEW VIEW OF THE MILKY WAY
On June 30, 2023, The IceCube collaboration announced that they have produced an image of the Milky Way galaxy using high-energy neutrinos. This study has established the galaxy as the source of high-energy neutrinos. This breakthrough was made possible by advanced machine learning and new data analysis tools, which have provided an entirely new perspective of our galaxy. The study included 60,000 neutrinos events spanning ten years of IceCube data.
The analysis focused on the southern sky, where the bulk of neutrino emission from the galactic plane is expected near the center of our galaxy. Until now, the background of muons and neutrinos produced by cosmic-ray interactions with the Earth’s atmosphere posed significant challenges. These high-energy neutrinos have energies millions to billions of times higher than those produced by the fusion reactions that power stars. “The strong evidence for the Milky Way as a source of highenergy neutrinos has survived rigorous tests by the collaboration,” says Ignacio Taboada, a professor of physics at the Georgia Institute of Technology and IceCube spokesperson. “Now the next step is to identify specific sources within the galaxy.” <
