From “Astronomy Magazine” : “Ghost particles caught streaming from dust-shrouded black hole”

From “Astronomy Magazine”

11.7.22
Mark Zastrow

The IceCube observatory in Antarctica has captured the best evidence yet that the galactic core of Messier 77 is producing neutrinos.

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U Wisconsin IceCube neutrino observatory

IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration.

Lunar Icecube.

IceCube Gen-2 DeepCore PINGU annotated.

IceCube neutrino detector interior.

IceCube DeepCore annotated.

DM-Ice II at IceCube annotated.


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The active galaxy Messier 77 as captured by the Hubble Space Telescope. Credit: A. van der Hoeven/The National Aeronautics and Space Agency/ The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganization](EU).

The origins of neutrinos are notoriously hard to pin down. The cosmos is flooded by these ghostlike particles, which come from all over the sky. But for years, neutrinos’ elusive nature meant astronomers could point confidently to just one galaxy known to produce them.

Now, there is strong evidence for a second: the bright spiral Messier 77 (NGC 1068) in Cetus. In a paper published Nov. 3 in Science [below], researchers report fresh observations from the IceCube neutrino observatory at the South Pole, plus improved analysis techniques that draw on machine learning. Combined, the results point to Messier 77 as the origin of 79 neutrinos that IceCube has detected over the past decade.

That interpretation suggests that the supermassive black hole at the dust-obscured heart of Messier 77 has a magnetic field that is acting as a powerful particle accelerator. But it also hints at answers to a larger astronomical mystery: how neutrinos are produced and how that process relates to other high-energy forms of light and matter that astronomers detect in the sky — cosmic rays and gamma rays.

In Messier 77, IceCube could be getting a glimpse of the origin of cosmic rays, says Francis Halzen, IceCube’s principal investigator and a particle physicist at the University of Wisconsin-Madison. In any case, Halzen is optimistic that more results will be forthcoming: “I think that we have the tools to solve the oldest problem in astronomy.”

Elusive particles

Theory predicts that neutrinos originate in some of the most energetic and violent regions of space: for instance, the cores of galaxies, when cosmic rays run into dust and radiation. The radioactive debris of such collisions eventually decays into neutrinos and gamma rays.

Observing this, however, is not easy. Neutrinos are not rare — roughly 100 trillion of them pass through your body every second. The difficulty is that unlike light, which is easily reflected or bent by mirrors and lenses, neutrinos barely interact with matter. A neutrino could travel through lead for a light-year before having a 50 percent chance of interacting with an atom.

In 2017, IceCube played a pivotal role in one of the first examples of a multi-messenger astronomy campaign, when the observatory detected a particularly energetic neutrino coming from a point in Orion. Follow-up observations from ground- and space-based telescopes — including NASA’s Fermi gamma-ray telescope — working across the electromagnetic spectrum showed that the neutrino likely came from a known blazar, TXS 0506+056, that was in the middle of producing a flare of gamma rays.


Blazars are prime candidates for generating neutrinos: They have central supermassive black holes spitting out jets of material at near-light speed aligned directly at Earth. However, the amount of neutrinos that IceCube has detected from TXS 0506+056 is much less than astronomers would expect if blazars were the sole source for all neutrinos seen across the sky.

This led astronomers to suspect that other types of galaxy could be producing neutrinos, too — ones whose gamma rays are “hidden,” perhaps obscured. An analysis of IceCube data published in 2020 [Physical Review Letters (below)]tentatively identified one such candidate galaxy: M77 in Cetus, roughly 30 million to 60 million light-years away. It appeared to be the source of dozens of neutrinos, despite the fact that its core lacks the powerful jets seen in blazars. It is “a clear example of such [a] gamma-ray obscured cosmic-ray accelerator,” Khota Murase, an astrophysicst at Penn State University who was not involved in the work, told Astronomy via email.

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This sky map produced from IceCube data depicts neutrino sources by the probability that they are not false positives. The circled spot in the northern hemisphere is Messier 77 — the most probable detection in the northern sky. Credit: IceCube Collaboration.

But the evidence as of 2020 wasn’t strong enough for the IceCube team to claim Messier 77 as a clear detection; according to the team’s analysis, the statistical significance was 2.9σ, meaning there was roughly a 1-in-500 chance that the build-up of neutrinos from Messier 77’s location could be a random occurrence. It left open the question, “Was this real, or were these fluctuations?” says Halzen. But with the new paper, he says, “we have now answered this question.”

Improved analysis

The new analysis includes a bevy of improvements, including machine-learning techniques to improve the accuracy of the neutrino tracks and their energies. The team says it also has a better understanding of the optical properties of the ice and IceCube’s directional sensitivity to neutrinos. These factors push the statistical significance of the find up to 4.2 σ. This is still short of the 5σ threshold that is considered the gold standard in physics, which equates to a probability that the signal could be a random error of just 1 in 3.5 million. Still, it is “great progress,” says Murase, who also penned a commentary for Science [below] accompanying the paper.

IceCube plans to keep up its momentum. During the South Pole summer season spanning 2025 and 2026, the observatory will be upgraded with more sensors and new calibration devices. The additions will improve the telescope’s sensitivity and also allow for another improved reanalysis of 15 years of data, says Halzen.

The team has also proposed a next-gen version of IceCube with eight times the volume of the current observatory, which would be capable of confirming sources like Messier 77 at the 5σ level and was endorsed by last year’s astronomy decadal survey.

Science papers:
Science
Physical Review Letters 2020
See this science paper for detailed material with images if the reader has proper credentials.
Commentary for Science

See the full article here .


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Astronomy is a magazine about the science and hobby of Astronomy. Based near Milwaukee in Waukesha, Wisconsin, it is produced by Kalmbach Publishing. Astronomy’s readers include those interested in astronomy and those who want to know about sky events, observing techniques, astrophotography, and amateur astronomy in general.

Astronomy was founded in 1973 by Stephen A. Walther, a graduate of The University of Wisconsin–Stevens Point and amateur astronomer. The first issue, August 1973, consisted of 48 pages with five feature articles and information about what to see in the sky that month. Issues contained astrophotos and illustrations created by astronomical artists. Walther had worked part time as a planetarium lecturer at The University of Wisconsin–Milwaukee and developed an interest in photographing constellations at an early age. Although even in childhood he was interested to obsession in Astronomy, he did so poorly in mathematics that his mother despaired that he would ever be able to earn a living. However, he graduated in Journalism from the University of Wisconsin Stevens Point, and as a senior class project he created a business plan for a magazine for amateur astronomers. With the help of his brother David, he was able to bring the magazine to fruition. He died in 1977.