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 The 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 supermassives black holes.
Neutrinos are weird. They are everywhere, but most of the time they do not interact with other particles or any kind of matter. That’s because they have very little mass and no electrical charge. For this reason, they are incredibly difficult to spot. But their total indifference to their surroundings also means that, unlike other particles, they are not distracted from their path, cruising great distances in straight lines from their sources. That 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 galaxy known as NGC 1086 (which is sometimes called Messier 77 or the Octopus Galaxy). NGC 1086 is a dusty galaxy, with a shape quite similar to it The Milky Way. However, NGC 1086 produces bursts of stars at a much higher speed than our galactic home and swirling around a black hole much more massive than the one at the center of the Milky Way.
This hungry black hole, gobbling up vast amounts of material, 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 crackle is hidden because the galaxy’s center is obscured by a thick ring when viewed from afar 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 a new tab). “When we observe neutrinos emitted by it, we will be able to learn more about the extreme particle acceleration and production processes happening inside the galaxy, which has not been possible until now as other high-energy emissions cannot escape it.”
The detection makes NGC 1068 only the second source of cosmic neutrinos ever identified. In 2018, the IceCube observatory detected 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, pointing directly at 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 obscured 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 on 86 vertical cables spaced 410 feet (125 meters) apart, the detectors record tiny flashes of blue light that are triggered when highly energetic neutrinos crash into the atomic nuclei of 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, such as 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 single out 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 one statement (opens in a new tab). “IceCube has collected around 80 teraelectronvolt 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, it obscured universe will open up, 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. The galaxy, discovered in 1780, is well known to astronomers and has been studied for centuries.
The study (opens in a new tab) is published in the journal Science on 4 November.