By Canadian Press

‘It’s humbling:’ Alberta scientists help track high-energy neutrino

Jul 12, 2018 | 2:28 PM

EDMONTON — Canadian scientists are part of an international team that has for the first time tracked a tiny, high-energy twist of matter to its source in deep space.

University of Alberta astronomer Greg Sivakoff says tracing a single neutrino to a black hole four billion light-years distant will give researchers a whole new way to probe the universe’s most exotic secrets — what astronomers call multimessenger astronomy.

“It’s like sitting down to a good meal,” said Sivakoff, one of five Canadians who are part of the team. 

“A good dish will look good, smell good, feel good and the taste will be good. A good meal will engage all of your senses.

“Multimessenger astronomy is the beginning of us sitting down to the meal and doing more than just looking at it. We’re beginning to have more than one sense.”

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The story begins last Sept. 22 at the IceCube observatory in Antarctica, a cubic kilometre of solid ice interlaced with thousands of sensors to detect subatomic particles.

That day, scientists detected an evanescent flash of blue light caused by a particle called a muon. This muon was special for two reasons. 

First, it carried a huge amount of energy — about 20 times as much energy as that generated in the largest man-made particle accelerator ever built. Second, it came from below, not above.  

“This particular particle was coming out from under the Antarctic ice,” Sivakoff said. “It couldn’t have been a muon that was generated in our atmosphere. It had to be a muon that was generated within the Earth itself and the only way you can do that is with a neutrino.”

Like a forensics team tracing the path of a bullet, scientists were able to combine data from different sensors within IceCube to deduce the original path of the neutrino.  

“This is how we were able to know where in the sky the neutrino was coming from.”

After comparing notes with colleagues around the globe, IceCube researchers were able to conclude the neutrino originated from a blazar, a type of galaxy with a super-massive black hole at its heart. It set out on its journey a little over four billion years ago, a time when life on Earth was just beginning.

The conclusion answered a big question in astronomy about how such high-energy particles are generated. It could go on to answer much more.

Until now, scientists have studied stars with visible light, electromagnetic radiation such as radio waves and, most recently, gravity waves. Discovering the source of high-energy neutrinos and tracking their path allows astronomers to use a completely new tool.

Much remains to be done before then. Scientists need to study more such neutrino events and link them with other sources to really understand how the process works.

But Sivakoff said multimessenger astronomy is eventually likely to answer questions about some of the universe’s most bizarre and spectacular phenomena — black holes, neutron stars, novas.

It’s akin to when Galileo first turned a telescope on the heavens.  

“Every time we open up a new window into the universe, we learn new things — not just things we expected,” Sivakoff said. “Oftentimes, those things we didn’t expect go on to be the biggest discoveries.

“It’s humbling.”

The discoveries were published Thursday in the journal Science.

— Follow Bob Weber on Twitter at @row1960

Bob Weber, The Canadian Press

Note to readers: This is a corrected story. An earlier version said Sivakoff’s first name was David.