ice cube/NSF
Since the French physicist Pierre Auger proposed in 1939 that cosmics rays must carry incredible amounts of energy, scientists have wondered what could be producing these powerful clumps of protons and neutrons raining down on Earth’s atmosphere. One possible means of identifying such sources is to trace the paths taken by high-energy cosmic neutrinos 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 the Ice Cube The Neutrino Observatory at the South Pole has now analyzed a decade of such neutrino detections and uncovered evidence that an active galaxy called Messy 77 (also known as the Squid Galaxy) is a strong candidate for one such high-energy neutrino emitter, according to a new paper published in the journal Science. It takes astrophysicists one step closer to solving the mystery of the origin of high-energy cosmic rays.
“This observation marks the beginning of being able to really do neutrino astronomy,” said Janet Conrad, an IceCube fellow at MIT. told APS Physics. “We have struggled for so long to see potential cosmic neutrino sources with very high significance and now we have seen one. We have broken a barrier.”
What we have previously reported, neutrinos travel near the speed of light. John Updike’s 1959 poem, “cosmic gallpays homage to the two most defining characteristics of neutrinos: they have no charge, and for decades physicists believed they had no mass (in fact, they have a tiny mass). Neutrinos are the most abundant subatomic particle in the universe. but they rarely interact with any kind of matter. We are constantly being bombarded every second by millions of these tiny particles, but they pass right through us without us noticing. That is why Isaac Asimov called them “ghost particles”.
Nicolle R. Fuller, IceCube/NSF
That low rate of interaction makes the neutrinos extremely difficult to detect, but because they are so light, they can escape unimpeded (and thus largely unchanged) by collisions with other particles of matter. This means they can provide valuable clues to astronomers about distant systems, in addition to what can be learned with telescopes across the electromagnetic spectrum, as well as gravitational waves. Together, these different sources of information have been called “multi-messenger” astronomy.
Most neutrino hunters bury their experiments underground, the better to cancel out noisy interference from other sources. In the case of IceCube, the collaboration features basketball-sized optical sensor arrays buried deep in the Antarctic ice. On the rare occasions that a passing neutrino interacts with the nucleus of an atom in the ice, the collision produces charged particles that emit UV and blue photons. Those are picked up by the sensors.
IceCube is therefore well positioned to help scientists advance their understanding of the origin of high-energy cosmic rays. As Natalie Wolchover convincingly explained in Quanta in 2021:
A cosmic ray is just an atomic nucleus: a proton or a group of protons and neutrons. However, the rare ones known as “ultra-high energy” cosmic rays have about as much energy as professionally served tennis balls. They are millions of times more energetic than the protons that hurtle down the circular tunnel of the Large Hadron Collider in Europa at 99.9999991% of the speed of light. In fact, the most energetic cosmic ray ever detected, dubbed the “Oh-My-God particle,” hit the sky in 1991 going something like 99.999999999999999999999951 percent of the speed of light, giving it about the energy of a bowling ball. which is dropped from the shoulder. height over a toe.
But where do such powerful cosmic rays originate? a strong possibility is active galactic nuclei (AGNs), which are found in the center of some galaxies. Their energies arise from supermassive black holes at the center of the galaxy and/or from the black hole’s spin.
