An international team of scientists including three University of Alabama researchers have discovered the first evidence of a source of cosmic particles known as high-energy neutrinos, a breakthrough that they say will enhance our understanding of how the universe is built and behaves.

The announcement on Wednesday coincided with the publication this week of two papers in the journal Science based on observations of high-energy neutrinos emitted from a galaxy billions of light-years away made by the IceCube Neutrino Observatory in Antarctica last fall and confirmed by telescopes around the globe and in Earth’s orbit. The IceCube team includes 300 scientists from 12 countries.

Marcos Santander, a UA assistant professor of physics and astronomy; Dawn Williams, a UA associate professor of physics and astronomy; and William C. Keel, a UA professor of physics and astronomy, were co-authors on the project.

“Today, I am proud to announce that using data gathered by NSF’s IceCube and an international coalition of scientists we have taken a major step toward solving the high-energy cosmic ray mystery,” said National Science Foundation Director France Córdova, at the NSF headquarters in Alexandria, Virginia.

Neutrinos are part of a century-old mystery about what sends cosmic rays and subatomic particles such as neutrinos speeding through the universe, said Francis Halzen, IceCube principal investigator, University of Wisconsin-Madison.

“It is one of the oldest open questions in astronomy. And of course the issue fascinates particle physicists because cosmic ray accelerators routinely accelerate particles to 10 million times the energy of the large hadron collider in Geneva,” Halzen said.

On Sept. 22, 2017, one high-energy neutrino passed through the ice lighting up the sensors, Halzen said. Computers at ICE CUBE reconstructed the energy and direction of neutrino and made it available for any telescope that was interested in it, he said.

Telescopes observing high-energy gamma rays were able to find the source, a flare in elliptical galaxy visible in the Orion constellation with a supermassive black hole at its center, spewing jets of mass and energy, the scientists said. The galaxy and its jets, known as a blazar when pointed at Earth, accelerate cosmic rays and particle collisions that create high-energy neutrinos.

The flare last fall was the largest ever observed from the blazar, said Regina Caputo, Fermi-Large Area telescope collaboration analysis coordinator, at University of Maryland/NASA Goddard Space Flight Center. The team behind the Fermi-Large Area telescope use the orbital telescope to constantly searching for changes in gamma rays. It observes more than 2,000 blazars in the sky, Caputo said.

When the IceCube team reviewed its decades worth of data, Halzen said it discovered in 2014 there was a flare in neutrinos, more than 12, that were recorded in a 150-day period. The energy distribution and pattern of the 2014 neutrinos exactly matched what they expected from cosmic accelerators, he said.

“For the first time, we have been able to associate high energy neutrinos with a high-energy gamma ray source. This is what we have been waiting for. This is the first evidence for a high-energy cosmic accelerator. A pivotal moment for multi-messenger astronomy,” said Olga Botner of Uppsala University.

Multi-messenger astronomy combines observation from multiple from devices such as gamma, X-rays, optical, radio telescopes. The team's discovery combined observations of the blazar from multiple instruments and data on the neutrino from IceCube.

“We’re beginning to do astronomy using means other than light, combining electromagnetic (light) observations with other measurements in what we now call multi-messenger astronomy,” said Marcos Santander, UA assistant professor of physics and astronomy, in a statement released by the university. “This is the first evidence that we have of an active galaxy emitting neutrinos, which means we may soon start observing the universe using neutrinos to learn more about these objects in ways that would be impossible with light alone.”

The IceCube Neutrino Observatory, funded in part by the NSF, was built in Antarctica to track the high-energy particles, Halzen said.

At the observatory, a sensor array of more than 5,000 digital optical modules is suspended along 86 cables embedded in a cubic kilometer of ice beneath the South Pole. The array is designed to observe evidence of the collisions between nearly mass-less neutrinos, capable of passing through most matter unimpeded, and the nuclei of the ice atoms.

The high energy neutrinos from cosmic events such as the births, collisions and deaths of stars stand out from the lower-energy neutrinos generated within our solar system and earth’s atmosphere.

High-energy neutrinos are of interest because of their tendency to travel great distances straight from their sources, typically without interference.

“A neutrino is invisible unless it collides with an atom. This happened very rarely, so you need to monitor a tremendous amount of atoms to stand a chance of catching a neutrino,” Botner said.

IceCube monitors 1 billion tons of ice at the South Pole station, she said. In the 2014 flare of neutrinos, 13 were detected through collisions in the ice, but Botner said more than 15 million passed by IceCube without a collision.

While the team has collected an incredible amount of data on the blazar, Halzen said the discovery of blazars as one source of high-energy neutrinos is only the beginning.

“These first results will raise new questions and open doors for new research. As in all good science, this is only the beginning and that is exciting,” Córdova said.


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