We Finally Know Where The Highest Energy Cosmic Rays Come From: Blazars
The way out in outer space is a class of objects called blazars. Think of them as extreme particle accelerators, capable of accumulating energy a million times more powerful than the Large Hadron Collider in Switzerland. It turns out that they are the cause of one of the great astrophysical mysteries: what creates and propels neutrinos across the universe at such blazing fast speeds? It turns out that the answer has been there all along: the blazar pumps out neutrinos and cosmic rays. That was the conclusion of a group of astronomers led by Dr. Sara Buson of the Universität Wurzburg in Germany as they study data from a very unique facility on Earth: the IceCube Neutrino Observatory in Antarctica.
Understanding the Origin of Speed Demon Particles
Neutrinos are quirky little ducks in the astrophysics zoo. They originate from cosmic ray interactions in the blazars and have a very small mass. Neutrinos do not interact with matter as they streak through the cosmos, meaning they travel through galaxies and planets. They even blow you up while you sit here and read this, and leave very little evidence for their part. Fortunately, that last characteristic means they can be traced back to their source because the electromagnetic force doesn’t even bother them.
So how did Buson and his team find the birthplace of the neutrino? They turn to the IceCube, which is buried deep in the ice at the South Pole. This is the most sensitive neutrino detector on the planet. He was looking for these nearly massless subatomic particles—which astronomers also call the astrophysical messengers. That’s because they carry information about violent astrophysical events and sources—such as black holes, neutron stars—and blazars.
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In 2017, IceCube detected a neutrino from blazar TXS 0506+056. This is the active core of a distant galaxy that is brighter than the rest of the galaxy. The data carried by the neutrino told the team that it originated in the heart of the blazar and traveled across 5.7 billion light years for the IceCube to measure. It doesn’t just transmit neutrinos—it’s also a bright radio source that emits light across the electromagnetic spectrum. (For the stargazers among us, this blazar is located towards the left shoulder of the constellation Orion.)
Blazars galore
Of course, TXS 0506+056 isn’t the only source of neutrinos (other than the Sun, for example). IceCube found 19 “hotspots” in the southern sky. At least ten of them are very likely blazers. “The results provide, for the first time, irrefutable observational evidence that the PeVatron blazar sub-sample is a source of extragalactic neutrinos and thus a cosmic ray accelerator,” Buson said in a press statement.
PeVatron blazars accelerate particles to at least PeV energy. PeV is short for “electron volt map” and 1015 electron-volts. To give you an idea of how powerful it is, the Large Hadron Collider hit a little over 1 PeV in 2015.
Neutrinos and Multi-Messenger Astronomy
These high-speed cosmic rays and nearly massless neutrinos are the newest “messengers” from the distant universe. For a long time, astronomers used light to study the universe. But, they’re not the only messengers out there who 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 messaging that carry valuable information about distant astrophysical events and objects.
According to team member Marco Ajello of Clemson University, multi-messenger astronomy adds immeasurably to our understanding of the universe. “It’s like feeling, hearing and seeing at the same time. You will get a much better understanding,” he said. “The same is true in astrophysics because the insights you have from the different detections of different messengers are much more detailed than you can get from light alone.”
Data provided by neutrinos and other messengers from distant universes points the way to a better understanding of objects like the blazars that created them. Team members will now focus on why and how blazars accelerate particles such as neutrinos. Obviously, they are very energetic objects. Blazar TXS 0506+056 is a typical active galactic core powered by a supermassive black hole. It has a relativistic radiance that points straight at us here on Earth, but fortunately, we are too far away to be harmed by it. Instead, we can watch as it generates neutrinos. In fact, it was the first known source of astrophysical neutrinos — and the very early provider of multi-messenger astronomy. Now astrophysicists have a new set of objects that act as probes of the distant universe.
For more information
Astrophysicists prove neutrinos came from blazar
Embark on a Journey through the Universe: Extragalactic Neutrino Discovery
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