We detect ‘ghost particles’ ejected from the heart of a galaxy covered in dust : ScienceAlert

The role of active supermassive black holes in the production of high-energy neutrinos outside the Galaxy appears to have been confirmed. For the second time, physicists have detected these so-called “ghost” particles at the heart of a galaxy in the gap of intergalactic space.

With this finding, we can begin a true inventory of extragalactic neutrino factories and use the properties of neutrinos to understand their home environment.

The galaxy in question is a well-studied object known as NGC 1068 – aka Messier 77 or the Squid Galaxy – a beautiful barred spiral located about 47 million light-years away, close enough to see with a pair of binoculars.

And scientists have counted dozens of neutrinos in the high-energy teraelectronvolt (TeV) range coming from its direction.

Previously, the only high-energy neutrino was a single TeV particle detected in an extragalactic source located in a type of galaxy called a blazar named TXS 0506+056, about 3.8 billion light-years away.

This makes the new collection of data, obtained over a 10-year period by the IceCube Neutrino Observatory, an absolute treasure.

“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,” says physicist Francis Halzen of the University of Wisconsin-Madison and principal investigator of IceCube.

“IceCube has collected about 80 teraelectronvolt neutrinos from NGC 1068, which are not yet enough to answer all of our questions, but are certainly the next big step toward realizing neutrino astronomy.”

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Neutrinos are nearly massless subatomic particles produced by radioactive decay that permeate the Universe.

They are constantly transported, through everything, among the most abundant particles in the Universe. They are streaming through you, right now. And that’s what makes them hard to detect: They interact with almost anything.

For a neutrino, normal matter in the Universe might as well be smoke and shadows. This is why we call them ghost particles.

It is precisely this quality, however, that makes them so potentially useful for study. Because they are not affected by the Universe, they always travel in a straight line.

And high-energy neutrinos are exclusively produced in processes involving the acceleration of cosmic rays, such as the powerful jets produced in the extreme environment around an active supermassive black hole.

If we want to learn about these neutrino factories, though, we need to find the neutrinos, and that’s where IceCube comes in. Buried in the frozen darkness beneath the dark ice of Antarctica, the photodetectors look for showers of light produced when neutrinos occasionally interact with atoms or molecules.

The IceCube observatory with the Milky Way above.
The IceCube laboratory at night, with the Milky Way visible above. (Martin Wolf/IceCube/NSF)

And that’s how a close, international collaboration, carefully analyzing 10 years of data collected by the observatory, was able to spot 80 high-energy neutrinos in the 1.5 to 15 TeV range tracing a straight line back to NGC 1068 .

NGC 1068, as we have already noted, is an active galaxy. It is a closed spiral, like the Milky Way. Unlike the Milky Way, the supermassive black hole at the heart of NGC 1068 is devouring matter from the space around it at a furious rate.

The black hole is surrounded around the equator by a massive torus and a disk of dust and gas. This orbits and feeds the black hole. gravity and friction on the ring and disk produce insane amounts of heat and light.

Not all material ends up beyond the black hole’s event horizon. Some of it, scientists believe, is accelerated along the black hole’s magnetic field lines at the poles, where it is ejected into space in the form of powerful jets of plasma that hurtle through space at nearly the speed of light.

If the jet is pointed in our direction, we call this galaxy a blazar. TXS 0506+056 is a blazar, and the analysis shows that the 300 TeV neutrino was produced in the Earth-pointing jet.

NGC 1068’s jet is not pointing in our direction. In fact, the galaxy is oriented in such a way that much of the high-energy light from the active galactic nucleus is obscured by dense dust. This means that neutrinos could be a way of detecting a black hole that is difficult to study otherwise.

“Recent models of the black hole environments in these objects suggest that gas, dust and radiation should block gamma rays that would otherwise accompany neutrinos,” says Michigan State University physicist Hans Niederhausen.

“This detection of neutrinos from the core of NGC 1068 will improve our understanding of the environments around supermassive black holes.”

The team interprets neutrinos as a signature of particle acceleration and says the discovery suggests that active galactic nuclei are a major contributor to the space-filling neutrino population.

They also say that the discovery is a breakthrough for neutrino astronomy and that NGC 1068 may, in the future, become one of the cornerstones of the field.

“Several years ago, NSF began an ambitious project to expand our understanding of the Universe by combining established capabilities in optical and radio astronomy with new capabilities to detect and measure phenomena such as neutrinos and gravitational waves,” says physicist Denise Caldwell of National Science Foundation. , which funded IceCube.

“The IceCube Neutrino Observatory’s identification of a nearby galaxy as a cosmic neutrino source is just the beginning of this new and exciting field that promises insights into the unexplored power of supermassive black holes and other fundamental properties of the universe.”

The research has been published in Science.

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