Blazars are feeding supermassive black holes that sit on the hearts of lively galaxies, blasting out enormous jets of radiation and matter. But unlike quasars, the cosmic twin of a blazar, these phenomena are pointed directly at Earth.
And in response to latest research, they may actually be pelting our planet with neutrinos — otherwise often known as “ghost particles.”
This spooky moniker comes from the very fact neutrinos are notoriously difficult to detect. They’re chargeless, and have virtually no mass. Around 65 billion neutrinos manage to stream through every square inch of your body each second with no discernible effect.
So unsurprisingly, neutrinos are considered the “ghosts” haunting the particle zoo. Fascinatingly, nonetheless, their ghost-like nature also makes them vital probes of the universe. It’s because neutrinos can “phase” through obstacles, akin to dense dust clouds, that impede other types of matter and even light.
Due to this fact, understanding where exactly neutrinos are coming from within the cosmos is significant. And this latest research brings scientists a step closer to establishing blazars because the source of the astrophysical ghosts.
Where gamma-rays are available in
Blazars are a subset of vivid, lively galactic nuclei (AGNs) or “quasars,” that are vivid enough to outshine the combined light of each star within the galaxy that houses them. Blazars are only different from standard quasars in that they keep our planet dead of their sights when emitting material from their cores at near-light speeds.
The jets emitted in blazar flare events are composed of high-energy particles often known as cosmic rays that may stretch across many light-years, even extending well beyond the bounds of the galaxies these phenomena are situated inside. These jets also consist of electromagnetic radiation starting from low-energy radio waves to extremely high-energy gamma rays.
And importantly, when cosmic rays interact with particles of sunshine , or photons , they’re believed to create showers of none apart from neutrinos. Thus, gamma-ray flares from AGNs have long-been the prime suspect within the hunt for neutrino particles detected in our sky.
The link between considerably less conspicuous AGN jets and neutrinos was solidified in 2017, when the IceCube neutrino detector buried deep under the North Pole spotted a high-energy neutrino event coinciding with the flare of a blazar called TXS 0506+056. They were connected by way of location and timing. TXS 0506+056 emerges from a supermassive black hole powered AGN situated around 5.7 billion light-years away from Earth.
Yet, the actual relationship between the blazar flare patterns and the quantity of neutrinos passing through Earth — the neutrino flux — remained shrouded in mystery.
‘On-duty’ gamma-ray blasting blazars
To resolve this puzzle, a global team of researchers decided to deeply take a look at TXS 0506+056 in addition to one other 144 blazars, contenders gleaned from the Fermi Large Area Telescope Monitored Source List.
This allowed the scientists to calculate the weekly flux of gamma-rays related to blazars and concurrently plot the sunshine curves of such high-energy events. The researchers then developed a “flare duty cycle” that shows the period of time a blazer spends in a flare state, and the way much energy this flare state accounts for on blazer light curves.
“We discover that blazars with lower flare duty cycles and energy fractions are more quite a few amongst our sample. Their flare duty cycles and energy fractions represent power law-like distributions [a relationship between two quantities, where a change in one quantity results in a change in the other that is proportional to a power of the change, independent of the initial size of both quantities] correlating strongly with one another,” Kenji Yoshida, team member and a researchers on the Shibaura Institute of Technology, said in a statement. “We found a big difference between blazar subclasses for the flare duty cycles on the 5% significant level.”
The team statistically assessed the neutrino flux from each gamma-ray flare and developed a scale relationship based on a blazar’s gamma-ray flux during more quiet periods. By comparing their neutrino predictions for every blazar for one-week and 10-year periods to the sensitivity of IceCube over time, the scientists were in a position to place upper limits on the contributions of the flares to neutrino flux.
“We hope that this study helps improve our understanding of the contribution of blazars to astrophysical neutrinos,” Yoshida concluded. “Application of the current method to further observations may need the potential to contribute to the advancement of scientific knowledge of the origin of astrophysical neutrinos.”
The team’s research was published in September in the Astrophysical Journal.