Science & Environment

Neutrinos from the cosmos hint at new era in astronomy

Image caption IceCube has more than 5,000 detectors to catch passing neutrinos

An experiment buried beneath the ice of the south pole has for the first time seen high-energy neutrino particles originating outside our Solar System.

They are produced in our atmosphere and in the cosmos's most violent processes, but the IceCube experiment has seen the first energetic "cosmic neutrinos".

It detected 28 of the exceptionally fast-moving neutrinos - but it remains unclear exactly where they came from.

The pioneering finds could herald an entirely new branch of astronomy.

The results were presented on Wednesday at the IceCube Particle Astrophysics Symposium in Wisconsin, US.

Image caption The experiment has captured a variety of neutrino events

Researchers have gathered there to discuss the findings of the world's largest neutrino detector, occupying a cubic kilometre. It is made up of 86 strings sunk into the Antarctic ice, each with 60 sensitive light detectors strung along it like "fairy lights".

As neutrinos pass, they very rarely bump into the nuclei of atoms in the ice, producing a brief flash that the detectors can catch. With more than 5,000 detectors catching flashes at different times, the direction of the neutrinos' arrival can be determined.

IceCube is just one of a number of neutrino detection experiments around the globe. Low-energy neutrinos from the dying throes of a star were spotted by Japanese researchers in 1987 - the first-ever neutrinos from beyond our cosmic neighbourhood, leading to the 2002 Nobel Prize in physics.

They can also be produced in the Sun and our own atmosphere here on Earth - IceCube picks up about 100,000 of those a year.

However, previous attempts to associate higher-energy neutrinos with more far-flung cosmic processes, such as those described in April 2012, had turned up nothing.

But in April this year, the IceCube collaboration reported seeing two neutrinos - nicknamed Bert and Ernie - of energies greater than a "petaelectronvolt".

That is 150 times higher than the energy to which particles within the Large Hadron Collider can currently be accelerated.

Now the team reports 26 more events, each higher than 50 teraelectronvolts (a twentieth of a petaelectronvolt), which they expect will also be of cosmic origin.

But Francis Halzen, principal investigator on the IceCube experiment, said that "of course, there's much more to do".

"It's after you find them that the work starts; these events are very difficult to analyse," Prof Halzen told BBC News.

Particle pictures

For centuries, stargazers have relied only on light of a wide range of wavelengths - many far beyond those we can see - to get pictures of the cosmos.

But these first cosmic neutrino detections open the possibility for doing astronomy instead using particles - developing pictures of the Universe's most active corners by analysing the directions and energies of the neutrinos they produce.

Prof Halzen recalled discussions with Frederick Reines, who shared the 1995 Nobel Prize in physics for first discovering the neutrino in the mid-1950s.

"He would tell me that as soon as he discovered that the neutrino was real, everybody had the idea that you had a particle that you could do astronomy with. In 1960, several people wrote rather detailed papers on how to do it."

Only later did it become clear that a detector as monumentally large as IceCube would be required to launch such a new era in astronomy - an era that for the first time seems to be taking shape.

"It is incredibly exciting to work with the final IceCube configuration," Prof Halzen said.

"It not only shows that we built the right detector, it promptly delivered results. What it means for astronomy is in our future, hopefully our very near future. The tools are in place and the first harvest of events is in."

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