Neutrinos are the smallest particles, with almost no mass. They are born in a wide variety of objects, from bananas to exploding supernovae. Most of them pass through the Earth without interacting with matter. That is why they are called "ghost particles."
The IceCube Observatory at the South Pole uses Antarctic ice as a detector. When a neutrino does collide with an ice molecule, instruments record faint radiation. In this way scientists catch particles with energies hundreds of thousands of times higher than those of neutrinos from the Sun. For this discovery IceCube recently received the Nobel Prize.
But exactly where these high-energy particles come from is not fully clear. One candidate is quasars: objects where black holes with masses millions of times that of the Sun tear matter apart. In 2017 IceCube detected a neutrino from the direction of the quasar TXS 0506+056 simultaneously with a flare of gamma radiation from it. This makes sense: the processes that produce neutrinos should also produce gamma rays. However, dust and gas around the black hole can block gamma radiation, preventing it from reaching Earth.
Radio waves, unlike gamma rays, pass through such obstacles more easily. Since 2017 the VLASS project in New Mexico has been monitoring changes in the brightness of radio sources. Recently my team showed that most objects with variable radio emission are quasars of the same type as the 2017 "suspect."
By comparing the arrival times of neutrinos with the moments of radio flares, we noticed a correlation - a statistical association that by itself does not yet prove causation. In other words, when IceCube registers a neutrino, a radio source in the same region of sky flares more often than by chance. But such a link is traced for only about 13% of recorded astrophysical neutrinos - the origin of most particles is still unexplained. Yet gamma-ray telescopes do not see at all more than 90% of the radio flares possibly associated with neutrinos.
The authors emphasize: the signal is intriguing, but the probability of a chance coincidence is about 1 in 30. It is like flipping heads five times in a row: unlikely, but possible. Scientists are used to reliability such as one case in a million. To test whether the link is real, new observations are needed - they are expected in the coming years. The work is published in The Open Journal of Astrophysics.