Big black hole shoots ghost particles

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Giant ice cube helps solve 100-year mystery

Energy beams from gigantic black holes could explain a centuries-old mystery behind cosmic rays, says a recent study.

An international team of researchers published two papers in Science this week on how they had traced a neutrino back to a giant black hole in a galaxy about 3.7 billion light years away.

Doing so involved scores of researchers and multiple satellite and ground-based observatories, including the IceCube facility in Antarctica – a unique research station that combines a bevy of detectors with a cubic kilometre of ice.

Neutrinos are uncharged particles and generally move in straight lines, which makes it very easy for us to determine their point of origin, said St. Albert astronomer Murray Paulson, who read about the studies. Researchers believe they can use them to determine the origins of ridiculously high-energy charged particles called cosmic rays, which swerve all over the place but also create neutrinos that occasionally hit Earth.

“We’re being pummeled by these things all the time,” Paulson said of cosmic rays, yet we’ve no idea what’s causing them.

Neutrinos are sometimes called “ghost particles” as they’re tough to detect and can pass through whole planets without hitting anything, said Gregory Sivakoff, a physics professor at the University of Alberta involved with this study. But since there are billions of them passing through every part of the Earth each second, if you have a big enough target – say, a cubic kilometre of ice – one of them will eventually hit it.

When a neutrino hits an atom in the IceCube, it creates a blue flash of light that researchers can use to triangulate its trajectory. Whenever this happens, the IceCube’s computers send an alert to observatories around the world so they can point their telescopes in that direction to find what shot out the particle.

While the sun and certain supernovas produce neutrinos, those are millions of times less powerful than the ones associated with high-energy cosmic rays, the origins of which have been a mystery for about a century, Sivakoff said. One theory was that a galaxy with a gigantic black hole in its centre – a blazar – could be the source, as their gravity was so intense that they created jets of ultra-fast particles.

Last Sept. 22, the IceCube station detected what appeared to be a neutrino from a high-energy cosmic ray. Space-based and ground-based detectors soon determined that a known blazar about 3.7 billion light years away had been shooting gamma rays at Earth at that moment and had also been doing so during about a dozen previous detections at IceCube. That led these researchers to conclude that these rays likely came from that blazar, Sivakoff said.

Researchers still have to determine if blazars are the only source of these cosmic rays or just one of them, Sivakoff said. More important in his mind is the fact that, for the first time, researchers have used a particle other than a photon to learn more about deep space.

“With neutrinos, we now have a new messenger that will tell us more about the universe.”

This is the first time that researchers have been able to conclusively link a flux of high-energy neutrinos to something producing them in space, Paulson said.

“It’s really cool to finally know where these things are coming from.”

 

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Kevin Ma

Kevin Ma joined the St. Albert Gazette in 2006. He writes about Sturgeon County, education, the environment, agriculture, science and aboriginal affairs. He also contributes features, photographs and video.