IceCube neutrinos provide new view of active galaxy
IMAGE: WHEN A NEUTRINO INTERACTS WITH MOLECULES IN THE CLEAR ANTARCTIC ICE, IT PRODUCES SECONDARY PARTICLES THAT LEAVE A TRACE OF BLUE LIGHT AS THEY TRAVEL THROUGH THE ICECUBE DETECTOR. view more
CREDIT: IMAGE: NICOLLE R. FULLER, ICECUBE/NSF
An international team of scientists, including researchers at the University of Adelaide, have gathered new evidence about the energetic core of an active galaxy millions of lights years away by detecting neutrino particles emitted by it.
The scientists have found that NGC 1068, also known as Messier 77, in the constellation of Cetus, is a high-energy neutrino emitter. They have observed the particles using the IceCube Neutrino Observatory in Antarctica.
“We are peering inside active regions of the NGC 1068 galaxy 47 million light years away,” says Associate Professor Gary Hill, from the University of Adelaide’s Department of Physics, School of Physical Sciences and member of the international IceCube Collaboration.
“As we observe neutrinos emitted by it we will be able to learn more about the extreme particle acceleration and production processes occurring inside the galaxy, which hasn’t been possible up to now as other high energy emissions can’t escape from it.”
Neutrinos are subatomic particles that normally pass, by the trillion, through our bodies and every part of the Earth every second, but they rarely interact with matter – a fact that makes them difficult to detect.
The observations were made by the IceCube Neutrino Observatory at the Amundsen-Scott South Pole Station, which was completed in late 2010. NGC 1068 is visible with large binoculars and has been the subject of many astronomical observations.
In 2018, IceCube found the first ever source of neutrinos emitted by TXS 0506+056, a very distant blazar, from which super-massive black hole-powered particle jets, pointing straight at Earth, emit neutrinos. This led to the joint observations over a short time period of neutrinos and gamma-rays.
The NGC 1068 galaxy is about 100 times closer and around 80 neutrino events have so far been identified from the active galaxy. In contrast to the TXS 0506+056 blazar, NGC 1068 is oriented relative to Earth in such a way that a direct view of the central emitting region is obscured by dust. Gamma-rays are absorbed but the neutrinos can escape uninhibited from these regions.
“After the excitement in 2018 of the discovery of neutrinos from TXS 0506+056, it’s even more thrilling to find a source producing a steady stream of neutrinos that we can see with IceCube,” says Associate Professor Hill.
“The fact that neutrinos can escape from within these otherwise-obscured regions of the universe means they are also hard to detect. This requires large detectors like IceCube, which is the current leader in the field with an instrumented volume of a cubic kilometre of deep South Pole ice.”
Many neutrinos pass clear through the Earth, but some interact in the ice near the detector and create muons, which emit flashes of light that are picked up by IceCube’s more than 5000 basketball-sized optical sensors spread over 86 strings, deployed into holes drilled to nearly 2500 metres depth and now permanently frozen into the deep ice. The patterns of light are used to infer the arrival directions and energies of the particles.
“One of the best aspects of my research journey so far has been the time I have spent at the South Pole over many summer seasons working on the installation teams deploying the detector strings into the ice” says Associate Professor Hill.
“The enormous size of IceCube required many years of effort from hundreds of people around the world to complete construction and understand the response to high energy particles. In a few years we’ll be back to the South Pole to put more instruments into the ice, as part of an effort to further improve the detector.”
A future expansion of the detector, dubbed IceCube-Gen2, would be able to detect many more neutrinos, resolve more of these sources and make observations at even higher energies.
The IceCube Neutrino Observatory is operated by the IceCube Collaboration, consisting of over 350 scientists at 58 institutions around the world: https://icecube.wisc.edu/collaboration/institutions
Major funding comes from the US National Science Foundation, and from funding agencies in all other participating countries. The University of Adelaide IceCube research is supported by the Australian Research Council.
The team’s results are published in the journal Science.
JOURNAL
Science
METHOD OF RESEARCH
Observational study
First neutrino image of an active galaxy
IceCube telescope: High-energy neutrinos discovered in galaxy NGC 1068
Peer-Reviewed PublicationIMAGE: PROF. DR. ELISA RESCONI view more
CREDIT: ANDREAS HEDDERGOTT / TUM
For over ten years the IceCube Observatory in the Antarctic has been monitoring the light traces of extragalactic neutrinos. While evaluating the observatory's data, an international research team led by the Technical University of Munich (TUM) discovered a high-energy neutrino radiation source in the active galaxy NGC 1068, also known as Messier 77.
The universe is full of mysteries. One of these mysteries involves active galaxies with gigantic black holes located at their centers. "Today we still don't know exactly what processes take place there," says Elisa Resconi, Professor for Experimental Physics with Cosmic Particles at TUM. Now her team has made a major step towards solving this puzzle: The astrophysicists have discovered a high-energy neutrino source in the spiral galaxy NGC 1068.
It's very difficult to investigate the active centers of galaxies using telescopes which detect visible light or gamma or X-ray radiation from space, because clouds of cosmic dust and hot plasma absorb the radiation. Only neutrinos can escape the infernos at the edges of black holes; these neutrinos have no electric charge and almost no mass. They permeate space without being deflected by electromagnetic fields or absorbed. This makes them very difficult to detect.
The greatest obstacle in neutrino astronomy has until now been the separation of the very weak signal from the strong background noise created by particle impacts from the earth's atmosphere. It took many years of measurements using the IceCube Neutrino Observatory and new statistical methods to make it possible for Resconi and her team to accumulate enough neutrino events for their discovery.
Detective work in the eternal ice
The IceCube telescope, located in the ice of the Antarctic, has been detecting the light traces resulting from incident neutrinos since 2011. "Based on their energy and their angle of incidence we can reconstruct where they come from," says TUM scientist Dr. Theo Glauch. "The statistical evaluation shows a highly significant cluster of neutrino impacts coming from the direction of the active galaxy NGC 1068. This means we can assume with a probability bordering on certainty that the high-energy neutrino radiation comes from this galaxy."
The spiral galaxy, 47 million lightyears away, was discovered as early as the 18th century. NGC 1068 – also known as Messier 77 – resembles our galaxy in shape and size, but has a highly luminous center which is brighter than the entire Milky Way, although the center is only approximately the size of our solar system. This center contains an "active core": a gigantic black whole with a mass of about one hundred million times that of our sun, which is absorbing large amounts of material.
But how and where are neutrinos generated there? "We have a clear scenario," says Resconi. "We think the high-energy neutrinos are the result of extreme acceleration which the matter in the vicinity of the black hole undergoes, raising it to very high energies. We know from particle accelerator experiments that high-energy protons generate neutrinos when they collide with other particles. In other words: We've found a cosmic accelerator."
Neutrino observatories for new astronomy
NGC 1068 is the statistically most significant source of high-energy neutrinos to be discovered as yet. More data will be necessary in order to be able to localize and investigate weaker and more distant neutrino sources, says Resconi, who recently launched an international initiative for the construction of a neutrino telescope several cubic kilometers in size in the northeast Pacific, the Pacific Ocean Neutrino Experiment, P-ONE. Together with the planned second-generation IceCube observatory – IceCube Gen2 – it will provide the data for the neutrino astronomy of the future.
JOURNAL
Science
ARTICLE TITLE
IceCube Collaboration: Evidence for neutrino emission from the nearby active galaxy NGC 1068
ARTICLE PUBLICATION DATE
3-Nov-2022
Nearby active galaxy NGC 1068 emits high-energy neutrinos
The IceCube Neutrino Observatory – a network of thousands of sensors located deep in the ice below the South Pole – has identified neutrino emission from NGC 1068, a nearby active galaxy also known as Messier 77. According to the study, the newly identified source’s properties are quite different from the high-energy blazar TXS 0506+56, which was previously identified as a neutrino source. The authors suggest that there is likely to be more than one population of sources contributing to the observed cosmic neutrino background. Observations have indicated that there is a diffuse background of neutrinos from extragalactic sources. These high-energy neutrinos are thought to be produced by cosmic rays when they collide with matter or radiation inside sufficiently energetic astrophysical objects, such as active galaxies containing supermassive black holes . However, identifying the individual sources that produce neutrinos remains challenging. Here, the IceCube Collaboration – an international group of more than 400 researchers – analyzed data collected with the IceCube Neutrino Observatory between 2011 and 2020 to search for point sources of neutrino emission. They identify the nearby active galaxy NGC 1068 as a source of high-energy neutrinos. In a related Perspective, Kohta Murase writes “Radio-quiet AGNs [active galactic nuclei], including NGC 1068, and other low-luminosity AGNs, which are more abundant than blazars and radio-loud AGNs, might help explain the amount of all cosmic neutrinos observed by the IceCube Neutrino Observatory.”
JOURNAL
Science
ARTICLE TITLE
Evidence for neutrino emission from the nearby active galaxy NGC 1068
ARTICLE PUBLICATION DATE
4-Nov-2022
IceCube neutrinos give us first glimpse into the inner depths of an active galaxy
IMAGE: HUBBLE IMAGE OF THE SPIRAL GALAXY NGC 1068. view more
CREDIT: NASA / ESA / A. VAN DER HOEVEN
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, to be published tomorrow (Nov. 4, 2022) in Science, were shared today in an online scientific webinar that gathered experts, journalists, and scientists from around the globe.
The detection was made at the National Science Foundation-supported IceCube Neutrino Observatory, a massive neutrino telescope encompassing 1 billion tons of instrumented ice at depths of 1.5 to 2.5 kilometers below Antarctica's surface near the South Pole. This unique telescope, which explores the farthest reaches of our universe using neutrinos, 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.
"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.”
Front view of the IceCube Lab at twilight, with a starry sky showing a glimpse of the Milky Way overhead and sunlight lingering on the horizon.
CREDIT
Credit: Martin Wolf, IceCube/NSF
The IceCube Neutrino Observatory is funded and operated primarily through an award from the National Science Foundation to the University of Wisconsin–Madison (OPP-2042807 and PHY-1913607). The IceCube Collaboration, with over 350 scientists in 58 institutions from around the world, runs an extensive scientific program that has established the foundations of neutrino astronomy. https://icecube.wisc.edu/collaboration/institutions
IceCube’s research efforts, including critical contributions to the detector operation, are funded by agencies in Australia, Belgium, Canada, Denmark, Germany, Italy, Japan, New Zealand, Republic of Korea, Sweden, Switzerland, Taiwan, the United Kingdom, and the United States. The IceCube EPSCoR Initiative (IEI) receives additional support through NSF-EPSCoR-2019597. IceCube construction was also funded with significant contributions from the National Fund for Scientific Research (FNRS & FWO) in Belgium; the Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG) in Germany; the Knut and Alice Wallenberg Foundation, the Swedish Polar Research Secretariat, and the Swedish Research Council in Sweden; and the University of Wisconsin–Madison Research Fund in the U.S.
+ info “Evidence for neutrino emission from the nearby active galaxy NGC 1068,” The IceCube Collaboration: R. Abbasi et al. DOI:10.1126/science.abg3395
JOURNAL
Science
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Evidence for neutrino emission from the nearby active galaxy NGC 1068
ARTICLE PUBLICATION DATE
4-Nov-2022
