NEUTRINOS STREAM FROM BLACK HOLE
WHEN COSMIC RAYS run into dust and radiation, they produce particles that eventually decay into gamma rays and neutrinos. These messengers flood the cosmos from all directions. But while gamma rays can be readily detected, neutrinos — which rarely interact with matter — are much harder. Until recently, astronomers could point confidently to just one galaxy known to produce them.
Now, there is strong evidence for a second: the bright spiral M77 (NGC 1068) in Cetus, around 45 million light-years away. In a paper published Nov. 3 in researchers report fresh observations from the IceCube neutrino observatory at the South Pole, plus improved analysis techniques that draw on machine learning. Combined, the results indicate M77 is the origin of 79 neutrinos that IceCube detected over the past decade. The IceCube team had tentatively reported M77 as a possible neutrino source in 2020, but the evidence wasn’t strong enough to claim a clear detection; the new analysis changes that.
The findings offer a glimpse into the supermassive black hole at M77’s heart, suggesting its magnetic field acts as a powerful particle accelerator that produces cosmic rays — which, in turn, create neutrinos and gamma rays.
But while M77 appears to be producing neutrinos, it is not particularly bright in gamma rays. It also lacks the blazing jets of near-lightspeed material that emanate from the only other known galaxy to produce neutrinos, the blazar TXS 0506+056.
Astronomers suspect that M77’s core may be one whose gamma rays are “hidden,” perhaps obscured by dust. Such galaxies and the cosmic rays they produce may be crucial in accounting for the number of neutrinos observed in the sky.