This is one of the highest-energy neutrino events from a survey of the northern sky superimposed on a view of the IceCube Lab at the South Pole. Credit: IceCube Collaboration
Researchers using the IceCube Neutrino Observatory have sorted through the billions of subatomic particles that zip through its frozen cubic-kilometer-sized detector each year to gather powerful new evidence in support of 2013 observations confirming the existence of cosmic neutrinos.
It heralds a new form of astronomy using neutrinos, the nearly massless high-energy particles generated in nature’s accelerators: black holes, massive exploding stars and the energetic cores of galaxies. In the new study, the detection of 21 ultra high-energy muons – secondary particles created on the very rare occasions when neutrinos interact with other particles -provides independent confirmation of astrophysical neutrinos from our galaxy + neutrinos from sources outside the Milky Way.
Those high-energy neutrinos, scientists believe, are created deep inside some of the universe’s most violent phenomena. The particles created in these events, including neutrinos and cosmic rays, are accelerated to energy levels that exceed the record-setting earthbound accelerators such as the Large Hadron Collider (LHC) by a factor of more than a million. The information they hold is pristine, unchanged as the particles travel millions of light years between their sources and Earth and promise insight into a host of problems in physics, incl how nature builds powerful and efficient particle accelerators in the universe.
The latest observations were made by pointing the Ice Cube Observatory – composed of thousands of optical sensors sunk deep beneath the Antarctic ice at the South Pole – through the Earth to observe the Northern Hemisphere sky. The Earth serves as a filter to help weed out a confusing background of muons created when cosmic rays crash into the Earth’s atmosphere. Between May 2010 and 2012, IceCube recorded >35,000 neutrinos but only ~20 events were at energy levels indicative of astrophysical or cosmic sources.
By instrumenting a cubic kilometer of deep Antarctic ice, scientists were able to make a detector big enough to capture the signature of the rare neutrino collision >>creates muon >>leaves a trail of Cherenkov light that faithfully mirrors the trajectory of the neutrino. The “optical sonic booms” created when neutrinos smash into another particle are sensed by the optical sensors that make up the IceCube detector array and, in theory, can be used to point back to a source. The neutrinos have energy levels identical to those seen when the observatory sampled the sky of the Southern Hemisphere. That suggests many of the potential sources of the highest-energy neutrinos are generated beyond the Milky Way. http://news.wisc.edu/23954
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