Blazars, the gas-consuming black holes at the heart of galaxies, may produce the majority of the neutrinos that Earth detects.
When the Large Hadron Collider was first activated, some thought it could create black holes that would consume the entire planet. When you realize that the universe can produce subatomic particles with a million times more energy than people and their machines, it is amusing to consider.
But what in the universe gives these small particles, known as cosmic rays, such amazing energy? Because the majority of these particles are negatively or positively charged, they must adhere to the curvature of braided magnetic field lines in the interstellar space.
The same mechanisms that generate cosmic rays also generate even smaller subatomic particles known as neutrinos. Sara Buson notes, “Astrophysical neutrinos are produced exclusively by mechanisms requiring cosmic ray acceleration” (Julius-Maximilians University, Germany). Since neutrinos are neutral, they are unaffected by magnetic fields and travel directly to Earth. Trace back the pathways of neutrinos to determine their origin.
In theory, this is the case, but in fact, it has not been so simple. The colossal IceCube neutrino observatory, buried 1.35 kilometers (0.8 miles) deep in the clear-blue ice of the South Pole, detects approximately 10 neutrinos each year with enough energy to demonstrate that they originate directly from space. (Cosmic rays striking the Earth’s atmosphere can yield lower-energy neutrinos that, while interesting in and of themselves, cannot be clearly attributed to cosmic origins.)
It is difficult to correlate high-energy neutrinos to astrophysical sources when there are so few of them and millions of potential sources. Now, however, Buson’s team claims to have accomplished this feat, linking the astrophysical neutrinos recorded by IceCube to blazars at the centers of galaxies. In such objects, a supermassive black hole consumes gas before expelling some of it in a jet that travels close to the speed of light.
10 out of 19 neutrino “hot spots” in the southern sky correspond to known blazars, according to a comparison between the distribution of neutrinos on the sky and a list of blazars published in a catalog called BZCat. The odds of this link being a mere coincidence are one in a million, according to Buson.
The findings, which will be published in the Astrophysical Journal, expand upon prior research that identified only a fragile connection between neutrinos and blazars. However, this research have concentrated on blazars that release gamma rays, which are high-energy photons that must originate from the jets of the black hole. Shock waves in the rush of plasma would create natural particle accelerators that are superior to anything created by humanity to yet.
In this instance, however, because Buson and his colleagues examined blazars that aren’t emitting many gamma rays, they demonstrated that the neutrinos aren’t coming from shocks in the jets themselves, but rather from the disk of gas swirling into the black hole, or possibly from gas above that disk that is just launching into the jet.
Researchers at the IceCube Observatory indicate that blazars indeed release gamma rays, but not simultaneously with neutrinos. A lack of target material in the jet prevents the jet from producing neutrinos. Nine of the ten gamma ray sources that Fermi missed were found in the new analysis, Halzen said. IceCube’s high-energy neutrinos may be traced back to the black hole’s surrounding environment, and this result shows that the requisite process for their generation exists there.