Ice Cube Detects A Galaxy Emitting Dense Neutrinos

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Ice Cube Detects A Galaxy Emitting Dense Neutrinos

High-energy neutrinos from the active galactic nucleus (AGN) at the center of galaxy Messier 77 have been detected by the Neutrino Observatory Icecube. Also known as NGC 1068, the galaxy contains a supermassive black hole, and the observation has opened a window into violent processes that are thought to produce cosmic rays.

Neutrinos are elusive particles that can easily pass through the Earth with little interaction with other matter. IceCube uses her one cubic kilometer of ice beneath Antarctica to observe extremely rare collisions between cosmic neutrinos and water molecules. These interactions create fast-moving charged particles that produce flashes of light in the ice called Cherenkov radiation. The light is captured by the ice’s network of over 5,000 detectors, allowing physicists in the IceCube collaboration to pinpoint where the neutrinos are coming from.

IceCube published his first observation of high-energy cosmic neutrinos in 2013, and five years later detected the first high-energy cosmic neutrinos from his AGN, of a type called a blazer.

Messier 77 as seen by Hubble
Particle accelerator: IceCube has detected 79 high-energy neutrinos from the Messier 77 galaxy, which appears in this image from the Hubble Space Telescope. (Courtesy: NASA/ESA/A van der Hoeven)

IceCube scientists are now reporting the largest yield of high-energy neutrinos ever. These are her 79 particles from galaxy M77, 47 million light-years away. The observations were recorded between May 2011 and May 2020, and the researchers believe the neutrinos originated from the core of her AGN in her M77. M77’s AGN is otherwise hidden from our view by a thick torus of dust and gas.

Cosmic-ray connection

Astrophysicists believe that 79 high-energy neutrinos were formed when charged particles, such as protons, were accelerated to high energies by the magnetic field within the AGN. Some of these accelerated particles escape the black hole and become cosmic rays. Others collide with particles or photons in the AGN to create some mesons. These mesons decay rapidly into gamma rays and neutrinos. In M77, gamma rays are attenuated by the galactic dust torus, but most neutrinos pass unimpeded, some eventually reaching Earth. It is very likely that the particle acceleration involves the strong twisted magnetic field present within the AGN. However, it is not clear where this magnetic acceleration occurs. Possible locations include the accretion disk of matter swirling around a supermassive black hole and the luminescent corona, a very hot region directly surrounding the black hole. Another possibility is that the acceleration occurs in the jet of material ejected from the AGN in a direction perpendicular to the accretion disk.

Her Frances Halzen of the University of Wisconsin-Madison, who led the IceCube collaboration, told Physics World that neutrinos originate from a region of her AGN called the “cocoon,” the core region of her AGN that contains matter. He said observations show that , is blown outward by the jet and envelops the corona.

No gamma rays detected

“The gamma-ray photons that are inevitably produced along with the neutrinos lose energy in the dense core and emerge at lower energies,” he explains. “This is underscored by the fact that the NASA Fermi gamma-ray satellite does not detect the source in the energy range of the neutrinos detected.”

The conventional view is that most particles and radiation emitted by an AGN originate in the hot accretion disc, however doubts have been growing as to the veracity of this thermal model of emission. Andy Lawrence of the University of Edinburgh points out that some AGNs have variable brightness, and these fluctuations occur too quickly to be associated with changes in the accretion disc. Lawrence, who is not involved in the IceCube collaboration, adds “It may be that a more sophisticated disc theory plus accompanying non-thermal emission in the disc corona or jet might do the trick.”

Indeed, this latest observation by IceCube seems to back up the idea that particle acceleration occurs in the corona of the AGN rather than in the accretion disc.

Next generation

Although the mystery of how particles are accelerated in an AGN cannot be solved with these 79 neutrinos, and upgrade of the detector called IceCube Generation 2 should be completed by 2033. According to Halzen, the second generation was developed to study neutrino sources such as AGNs. “This detector has more than eight times the volume of his IceCube, and best of all, angular resolution. Combining the two, he said, instead of 10 years, he’s detected with a year’s worth of data.” will be possible.”

Messier 77 is a well-studied galaxy by amateur and professional astronomers. Therefore, by understanding how M77 produces high-energy neutrinos, M77 could become a Rosetta Stone for understanding other active galaxies.


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