A unique observatory buried in pristine Antarctic ice detected a stream of elusive neutrino particles streaming from the center of a distant galaxy obscured by dust.
The observation of IceCube observatory at the South Pole is only the second discovery of a source of cosmic neutrinosand scientists hope it can shed light on what happens inside the supermassive black holes.
Neutrinos are odd. They are everywhere but for the most part they do not interact with other particles or any type of matter. This is because they have very little mass and no electrical charge. For this reason, they are incredibly difficult to detect. But their complete indifference to their surroundings also means that, unlike other particles, they are not distracted from their path and cruise over vast distances in straight lines from their sources. This means that once astronomers know how to detect them, they can trace neutrinos to their origins much more easily than other types of particles.
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An international team of researchers has now reported detecting such a stream of neutrinos from a the galaxy known as NGC 1086 (which is sometimes called Messier 77 or the Squid Galaxy). NGC 1086 is a dusty galaxy, with a shape quite similar to it Milky Way. However, NGC 1086 does produce bursts stars at much higher speeds than our galactic home and swirling around a black hole far more massive than the one at the center of the Milky Way.
Devouring vast amounts of material, this hungry black hole forms the core of a sparkling active galactic nucleus that emits bright bursts of high-energy cosmic rays and charged particles that outshine the galaxy’s stars. However, most of the black hole’s crackling is obscured from view because the galaxy’s center is obscured by a thick ring when viewed from The earth. However, the neutrinos, with their ability to pass through matter, escape this ring and reach our planet undisturbed.
“We are peering into active regions of the NGC 1068 galaxy 47 million light-years away,” said Gary Hill, an associate professor of physics at the University of Adelaide in Australia and one of the authors of the paper. statement (opens in new tab). “By observing neutrinos emitted by it, we will be able to learn more about the extreme particle acceleration and production processes taking place inside the galaxy, which has not been possible until now because other high-energy emitters cannot escape from it.”
The detection makes NGC 1068 only the second source of cosmic neutrinos ever identified. In 2018, the IceCube observatory found a stream of neutrinos coming from an active galactic nucleus in a galaxy known as TXS 0506+056.
That galaxy, located in the constellation Orion, is 100 times farther from Earth than NGC 1068 but emits a jet of material at nearly the speed of light that points directly toward Earth. That makes any radiation coming from TXS 0506+056 much easier to detect than that from NGC 1068.
“After the excitement in 2018 of the discovery of neutrinos from TXS 0506+056, it is even more exciting to find a source that produces a steady stream of neutrinos that we can see with IceCube,” Hill said. “The fact that neutrinos can escape from these otherwise dark regions of the universe means that they are also difficult to detect.”
The IceCube observatory is a unique installation. It consists of over 5,000 detectors submerged at depths of 0.9 to 1.5 miles (1.5 to 2.5 kilometers) in the pristine Antarctic ice. Suspended from 86 vertical cables spaced 410 feet (125 meters), the detectors record tiny flashes of blue light that are triggered when high-energy neutrinos crash into the atomic nuclei of the ice molecules.
The observatory, built in the 2000s, has been in operation since 2010. The recent study analyzed detections of high-energy neutrinos made between 2011 and 2020, looking for possible sources of these particles among known active galaxies. Computer modeling previously suggested that active black holes, like the one at the center of NGC 1068, must be able to accelerate particles and eject them into intergalactic space along with bursts of high-energy radiation. Scientists expect other similar galaxies to produce their very own neutrino streams.
“One neutrino can pinpoint a source. But only an observation with multiple neutrinos will reveal the hidden core of the most energetic cosmic objects,” Francis Halzen, professor of physics at the University of Wisconsin–Madison and principal investigator of the IceCube project, said in a separate statement (opens in new tab). “IceCube has collected about 80 teraelectronvolt energy neutrinos from NGC 1068, which are not yet enough to answer all our questions, but they are definitely the next big step towards the realization of neutrino astronomy.”
Astronomers are currently planning a second-generation IceCube detector that will be able to detect a thousand times more neutrinos and detect five times fainter sources. Gradually, the astronomers said, the dim universe will open, ushering in a new era in astronomy.
NGC 1068 could become a “standard light” for this future neutrino research, Theo Glauch, a postdoctoral fellow at the Technical University of Munich (TUM) in Germany and co-author of the paper, said in the statement. Discovered in 1780, the galaxy is well known to astronomers and has been studied for centuries.
The study (opens in new tab) will be published in the journal Science on November 4.
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