blazar

We finally know where the most energetic cosmic rays come from: blazars

Far out in space there is a class of objects called blazars. Think of them as extreme particle accelerators capable of collecting energies millions of times more powerful than the Large Hadron Collider in Switzerland. They turn out to be the culprits in one of the great astrophysical mysteries: What creates and propels neutrinos through the universe at breakneck speed? It turns out the answer was always there: blazars emit neutrinos and cosmic rays. This was the conclusion reached by a group of astronomers led by Dr. Sara Buson of the University of Würzburg in Germany as they examined data from a very unique facility here on Earth: the IceCube Neutrino Observatory in Antarctica.

Understand the origins of Speed ​​Demon Particles

Neutrinos are strange little ducks in the astrophysical zoo. They originate from interactions with cosmic rays in blazars and have very little mass. Neutrinos don’t interact with matter as they zoom through the cosmos, meaning they travel through galaxies and planets. They shoot right through you even as you sit here reading this, leaving very little evidence of their passing. Luckily, this last quality means they can be traced back to their sources, since electromagnetic forces don’t even bother them.

The IceCube Neutrino Observatory at the South Pole. It detected neutrinos and helped astronomers trace them back to blazars. Photo credit: Emanuel Jacobi/NSF.

So how did Buson and her team find the sites where neutrinos are born? They turned to IceCube, which is buried deep in the ice at the South Pole. It is the most sensitive neutrino detector in the world. It searches for these nearly massless subatomic particles – which astronomers like to call astrophysical messengers. That’s because they contain information about violent astrophysical events and sources – like black holes, neutron stars – and blazars.

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In 2017 IceCube discovered a neutrino from the blazar TXS 0506+056. It is the active nucleus of a distant galaxy that is brighter than its entire galaxy. The data carried by the neutrino told the team it had emerged from the heart of this blazar and traveled 5.7 billion light-years to be measured by IceCube. Not only does it emit neutrinos — it’s also a bright radio source, pumping light across the entire electromagnetic spectrum. (For the stargazers among us, this blazar is toward the left shoulder of the constellation of Orion.)

Blazars abound

Of course, TXS 0506+056 is not the only source of neutrinos (apart from the Sun, for example). IceCube found 19 “hotspots” in the southern sky. At least ten of them are very likely blazars. “The results provide, for the first time, indisputable observational evidence that the subsample of PeVatron blazars are extragalactic neutrino sources and thus accelerators of cosmic rays,” Buson said in a press release.

PeVatron blazars accelerate particles to at least PeV energies. PeV is the abbreviation for “peta electron volts” and is 10fifteen electron volts To give you an idea of ​​how powerful this is, the Large Hadron Collider got just over 1 PeV in 2015.

Neutrinos and multi-messenger astronomy

These near-massless, fast-moving cosmic rays and neutrinos are the newest “heralds” from the distant universe. Astronomers have long used light to study the universe. But it’s not the only messenger out there that can teach us about stars, planets, galaxies, black holes, and other objects in the cosmic zoo. Neutrinos, cosmic rays, and gravitational waves provide other means of communication that carry valuable information about distant astrophysical events and objects.

According to team member Marco Ajello of Clemson University, multi-messenger astronomy contributes immeasurably to our understanding of the universe. “It’s like feeling, hearing and seeing at the same time. You’ll get a much better understanding,” he said. “The same is true for astrophysics, because the insights you get from multiple detections from different messengers are much more detailed than you can get with just light.”

The data from neutrinos and other messengers from the distant universe point the way to a better understanding of the objects such as blazars that generate them. Team members will now focus on why and how blazars accelerate particles like neutrinos. Obviously, they are extremely energetic objects themselves. Blazar TXS 0506+056 is a typical active galactic core powered by a supermassive black hole. It has a relativistic jet pointing straight at us here on Earth, but luckily we’re too far away to be hurt by it. Instead we can watch it produce neutrinos. In fact, it is the first known source of astrophysical neutrinos – and a very early proponent of multi-messenger astronomy. Now astrophysicists have a whole new set of objects that act as probes of the distant Universe.

For more informations

Astrophysicists prove that neutrinos come from blazars
Beginning of a journey through the universe: the discovery of the extragalactic neutrino
factories

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