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IceCube neutrino analysis determines possible galactic source of cosmic rays

IceCube neutrino analysis determines possible galactic source of cosmic rays

An artist's rendering of a cosmic neutrino shining above the IceCube observatory at the South Pole.  Under the ice are photodetectors that capture neutrino signals.
Increase / An artist’s rendering of a cosmic neutrino shining above the IceCube observatory at the South Pole. Under the ice are photodetectors that capture neutrino signals.

IceCube/NSF

Since the French physicist Pierre Auger proposed in 1939 that cosmic rays must carry incredible amounts of energy, scientists have puzzled over what could produce these powerful clusters of protons and neutrons that fall into Earth’s atmosphere. One possible means of identifying such sources is to retrace the paths that high-energy cosmic neutrinos traveled on their way to Earth, as they are created by cosmic rays colliding with matter or radiation, producing particles that then decay into neutrinos and gamma rays.

Scientists with An ice cube The South Pole Neutrino Observatory has now analyzed a decade’s worth of such neutrino detections and discovered evidence that the active galaxy is the so-called Messier 77 (aka the squid galaxy) is a strong candidate for one such high-energy neutrino emitter, according to new paper published in the journal Science. This brings astrophysicists one step closer to solving the mystery of the origin of high-energy cosmic rays.

“This observation marks the dawn of the possibility to actually do neutrino astronomy,” IceCube member Janet Conrad of MIT he told APS Physics. “We’ve struggled for so long to see potential cosmic neutrino sources of very high significance, and now we’ve seen one. We’ve broken the barrier.”

As we reported earlier, neutrinos they travel close to the speed of light. John Updike’s 1959 poem, “Cosmic Gall,” pays tribute to two of the most important characteristics of neutrinos: they have no charge, and for decades physicists believed they had no mass (in fact, they have a small fraction of mass). Neutrinos are the most abundant subatomic particle in the universe, but they very rarely interact with any kind of matter. seconds are bombarded by millions of these tiny particles, and yet they pass through us without us even noticing. That’s why Isaac Asimov called them “ghost particles.”

When a neutrino interacts with molecules in pure Antarctic ice, it produces secondary particles that leave a trail of blue light as they travel through the IceCube detector.
Increase / When a neutrino interacts with molecules in pure Antarctic ice, it produces secondary particles that leave a trail of blue light as they travel through the IceCube detector.

Nicolle R. Fuller, IceCube/NSF

That low interaction rate creates neutrinos extremely difficult to detect, but because they are so light, they can escape unhindered (and therefore largely unchanged) by collisions with other particles of matter. This means they can provide astronomers with valuable clues about distant systems, augmented by what can be learned from telescopes across the electromagnetic spectrum as well as gravitational waves. Together, these different sources of information have been called “multimessenger” astronomy.

Most neutrino hunters bury their experiments deep underground to cancel out noisy interference from other sources. In the case of IceCube, the collaboration involves an array of basketball-sized optical sensors buried deep within the Antarctic ice. On those rare occasions when a passing neutrino interacts with the nucleus of an atom in the ice, the collision produces charged particles that emit UV and blue photons. These are the sensors.

So IceCube is well positioned to help scientists advance their knowledge of the origins of high-energy cosmic rays. As persuasive Natalie Wolchover explained in Quanta in 2021:

Cosmic rays are just the atomic nucleus — a proton or a combination of protons and neutrons. However, those rare ones known as “ultra high energy” cosmic rays have as much energy as professionally served tennis balls. They are millions of times more energetic than protons hurtling around the circular tunnel of the Large Hadron Collider in Europe at 99.9999991% the speed of light. In fact, the most energetic cosmic rays ever detected, called the “Oh-My-God particle,” hit the sky in 1991, traveling at about 99.999999999999999999999951 percent of the speed of light, giving it about the energy of a ball being dropped from a ball. height to toe.

But where do such powerful cosmic rays come from? One strong possibility is active galactic nuclei (AGNs), found in the center of some galaxies. Their energy comes from the supermassive black holes at the center of the galaxy and/or from the spin of the black hole.



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