“Where exactly in the active galaxy, the neutrinos are produced will be a matter of debate,” he added in an email. “It is clear that the supermassive black hole provides the accelerator power,” he said, but how is a mystery.
The discovery is being announced in a series of papers by an international array of physicists and astronomers in Science and the Astrophysical Journal, and in a news conference sponsored by the National Science Foundation, which funds the IceCube Neutrino Observatory at the Amundsen-Scott South Pole Station.
“I think this is the real thing,” said John Learned, a neutrino expert at the University of Hawaii who is not part of IceCube, in an email, “the true beginning of high energy neutrino astronomy, of which we have dreamed for many decades.” Now, he added, “we will start seeing into the guts of the most energetic objects in the universe.”
Neutrinos are among the most plentiful particles in the universe — far outnumbering the protons and electrons out of which we are composed. They have no electrical charge and so little mass that it has not been accurately measured yet. They interact with other matter only by gravity and the so-called weak nuclear force and thus flow through us, Earth and even miles of lead like ghosts.
Yet in theory they are all over. Produced by radioactive decays of other particles, they are flooding us from nuclear reactions in the sun, distant supernova explosions and even the Big Bang. The previous great moment in neutrino astronomy happened in 1987, when some 25 neutrinos were recorded in three detectors on Earth coincident with a supernova explosion in the Large Magellanic Cloud, a nearby galaxy.
The lure of neutrinos for astronomy is that it is possible to trace them back to their origins. Not only do they fly long distances and from otherwise impenetrable spots like the cores of stars at virtually the speed of light, but by not having an electrical charge they are not affected by interstellar and intergalactic magnetic fields and other influences that scramble the paths of other types of cosmic particles, like protons and electrons. Neutrinos go as straight through the universe as Einsteinian gravity will allow.
IceCube, an international observatory run by 300 scientists from 12 countries, consists of more than 5,000 sensitive photomultiplier tubes embedded in grid encompassing a cubic kilometer of ice at the South Pole. When a neutrino very, very, very, very, very rarely hits an atomic nucleus in the ice, it produces a cone of blue light called Cerenkov radiation that spreads through the ice and is picked up by the photomultipliers.