Discovery of a second source of the ‘ghosts’ of the universe – Science & Technology

From the ice of the South Pole, the international IceCube experiment has intercepted a new source of the ‘ghosts’ of the universe, cosmic neutrinos: it is Messier 77 (also known as NGC 1068), one of the most studied active galaxies close to us hosting a voracious supermassive black hole. Its characteristics are different from those of the first cosmic neutrino source identified in 2018, the blazar (i.e. an active galaxy with a supermassive black hole in the center) TXS 0506 + 56, and this suggests that there are different types of neutrino sources. . The discovery is published in Science.

“We are peering into the active regions of the galaxy NGC 1068 47 million light years away,” says Gary Hill, a physicist at the University of Adelaide in Australia and a member of the international IceCube collaboration. “By observing the neutrinos it emits, we will be able to better understand the extreme processes of production and acceleration of particles that take place inside the galaxy, which has been impossible so far because other high-energy emissions cannot get out of it.”

“The detection of neutrinos from the heart of NGC 1068 will improve our understanding of the environment surrounding supermassive black holes,” adds Hans Niederhausen of Michigan State University. This is precisely the advantage of neutrino astronomy, which studies the universe using these ghost particles that interact so weakly with matter that they pass through it without a trace.

In 2018, the IceCube telescope (located between 1.5 and 2.5 kilometers below the surface of the ice at the South Pole at the Amundsen-Scott station) identified the first source of cosmic neutrinos in the TXS 0506 + 056 blazar, 4 billion away. of light years from us: the fact that the jets of particles emitted by the black hole were directed towards the Earth, made it possible to observe neutrinos and gamma rays together in a short period of time. The galaxy NGC 1068 is 100 times closer to us, but it is oriented in such a way that the dust prevents direct observation of the central region from which the emissions originate. Gamma rays are absorbed, while neutrinos can escape. “After the excitement in 2018 for the discovery of neutrinos from TXS 0506 + 056, it is even more exciting to find a source that produces a continuous jet of neutrinos that we can see with IceCube,” comments Hill.

“In 2013 the IceCube telescope discovered the existence of high-energy cosmic neutrinos from the depths of the Antarctic ice”, recalls Elisa Bernardini, professor at the University of Padua (the only Italian institution in IceCube) and associated with Infn (National Institute of Nuclear Physics ). “Almost 10 years after this revolutionary discovery, which opened a new observational window on the universe, the mechanisms behind these evanescent particles are still the subject of intense research and theoretical conjecture. The markedly different characteristics of the two sources identified to date suggest that there are at least two populations of astrophysical objects responsible for the emission of high-energy neutrinos. TXS 0506 + 056 and NGC 1068 contribute about one percent to the diffuse flux of cosmic neutrinos discovered by IceCube: the hunt for sources – concludes the expert – has therefore just begun ”.