(ORDO NEWS) — Some of the brightest and most energetic objects in the universe are a mysterious source of high-energy cosmic neutrinos, a new study has confirmed.
Comprehensive analyzes have linked galaxies with flaming cores known as blazars to these enigmatic particles rather convincingly.
This result provides a truly unexpected solution to a problem that has puzzled astrophysicists for years.
“These results provide, for the first time, incontrovertible observational evidence that a subsample of PeVatron blazars are extragalactic neutrino sources and therefore cosmic ray accelerators,” says astrophysicist Sarah Buson of Julius Maximilian University in Würzburg, Germany.
Neutrinos are strange things at the best of times. These subatomic particles are ubiquitous and are among the most abundant in the universe.
However, their mass is almost zero, they are electrically neutral, and they interact very little with anything else in the universe. For neutrinos, ordinary matter, which makes up most of the universe, may turn out to be only a shadow; that is why they are called ghost particles.
We know pretty well where neutrinos come from – normal neutrinos.
They are formed as a result of radioactive decay, which is quite common. Most of the neutrinos we detect on Earth are by-products of nuclear reactions in the Sun, but they can also be produced by supernovae, artificial nuclear reactions, or interactions between cosmic rays and atoms, for example.
But a special observatory in Antarctica has detected some really strange neutrinos.
Although neutrinos interact little with ordinary matter, they do from time to time. When they interact with molecules in water atoms, they can cause a very small flash of light.
The IceCube neutrino observatory has detectors embedded deep in the Antarctic ice at the south pole that can detect these flares. These detections make it possible to determine the energy of the neutrino.
In 2012, IceCube discovered two neutrinos that were unlike anything we’ve ever seen. Their energy was at the level of petaelectronvolt (PEV) – 100 million times more energetic than the neutrinos of supernovae. And these high-energy neutrinos came from intergalactic space, the source is unknown.
In 2018, we received a hint regarding this source. Because neutrinos don’t interact with each other, they move in a straight line through space, which is why a huge international collaboration of scientists has been able to track the high-energy neutrino to a blazar.
This is the core of a massive galaxy, powered by an active supermassive black hole, located at such an angle that jets of ionized matter, accelerated almost to the speed of light, are directed directly at the Earth.
“It’s interesting that there was a consensus in the astrophysicist community that blazars were unlikely to be sources of cosmic rays, and here we are,” said physicist Francis Halzen of the University of Wisconsin-Madison at the time.
However, some questions remained about the relationship between blazars and high-energy neutrinos. So a group of scientists led by Buson did what scientists do: they set about excavating.
They took 7 years of full-sky neutrino data from IceCube and painstakingly compared it to a catalog of 3,561 objects that are either confirmed blazars or have a high probability of being.
They did a positional cross-match of these catalogs, trying to determine whether high-energy neutrinos could be definitively linked to the location of blazars in the sky.
“With these data, we had to prove that blazars whose directional positions coincide with those of neutrinos are not there by chance,” explained astrophysicist Andrea Tramaser from the University of Geneva in Switzerland.
“By rolling the dice several times, we found that the random association can only exceed the association of real data once in a million trials! This is strong evidence that our associations are correct.”
According to the team’s analysis, the probability of a random match is 0.0000006. This suggests that at least some blazars are capable of producing high-energy neutrinos, which in turn helps solve another problem.
The origin of high-energy cosmic rays – protons and atomic nuclei rushing through space at a speed close to the speed of light – is also a big mystery.
According to Buson, high-energy neutrinos are produced exclusively in processes associated with the acceleration of cosmic rays. This means we can now relate blazars to the acceleration of cosmic rays, the team says.
“The process of accretion and the rotation of the black hole lead to the formation of relativistic jets in which particles are accelerated and emit radiation with an energy of a thousand billion times that of visible light!” Tramaser said.
“The discovery of a link between these objects and cosmic rays could be the Rosetta Stone of high-energy astrophysics.”
It follows that there are several areas that require further study. One is to try to figure out why some blazars are efficient particle accelerators and others are not. This will help the team figure out what the characteristics of the neutrino factory are and where else in space we can find them.
In addition, further, more detailed analysis of the neutrino data may lead to new discoveries about the birthplaces of these unusual, ghostly particles.
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