Scientists have been mystified by cosmic rays since they were found more than a century ago, pouring down onto Earth. Despite their huge number and intense power, it has been unclear where they come from. The new discovery could finally explain where cosmic rays originate. If correct, the answer would be a fittingly spectacular phenomenon deep in the universe. The neutrinos appear to be spewing out of fast spinning supermassive black holes and the discovery could give us an entirely new way of looking at the universe. The particles might be a “third messenger” carrying energy from elsewhere in the cosmos, in addition to light and gravitational waves.
If so, the newly observed particle would be an unprecedented new way of understanding some of the most intense and mysterious phenomena in the universe. Neutrinos could be doubly helpful because they have no mass and travel in an almost entirely straight line through the universe – which makes them very difficult to detect but very easy to track, as they travel billions of light years. “Neutrinos rarely interact with matter,” said Professor Paul O’Brien, a member of the international team of astronomers at the University of Leicester. “To detect them at all from the cosmos is amazing, but to have a possible source identified is a triumph. “This result will allow us to study the most distant, powerful energy sources in the universe in a completely new way.”
The discovery was reported in two new papers published in the journal Science, and was the result of work by a huge global team of researchers. “These intriguing results also represent the remarkable culmination of thousands of human years [worth] of intensive activities by the IceCube Collaboration, to bring the dream of neutrino astronomy to reality,” said Darren Grant, a professor of physics at the University of Alberta, and spokesman of the IceCube Collaboration, an international team with more than 300 scientists in 12 countries.
The neutrino was found on September 22 by the IceCube observatory, a huge facility a mile beneath the South Pole. A grid of more than 5,000 super sensitive sensors picked up the characteristic blue “Cherenkov” light emitted as the neutrino interacted with ice. Having almost no mass and passing right through planets, stars and anything else in its way, the particle travelled in a straight line from its point of origin to Earth. As a result, astronomers were able to track its trajectory back across billions of light years to its probable source.
News of the detection sent astronomers into a frenzy as telescopes were pointed in the suggested direction. The search led to a “blazar”, a special class of galaxy containing a supermassive black hole four billion light years away, just to the left of the constellation Orion. The finding was the result of a global effort to track down the source, triggered by an automated alert after the intriguing detection at the South Pole. “This result really highlights the importance of taking a multimessenger approach to these searches,” said Erik Blaufuss, a research scientist in the UMD Department of Physics who led the effort – over several years – to create and deploy IceCube’s high energy event alert system. “Any one observation made alone would likely not have let us piece together what is actually going on inside this source.”
A key feature of blazars is twin jets of light and elementary particles that shoot from the poles of the swirling whirlwind of material surrounding the black hole. One of those jets happened to point towards Earth and led to one of the most profound discoveries in the history of astrophysics. The neutrino detected by IceCube is thought to have been created by high energy cosmic rays from the jets interacting with nearby material. Unlike high energy neutrinos, most cosmic rays carry an electric charge that causes their trajectories to be warped by magnetic fields, making it impossible to trace their origins. By contrast, neutrinos are unaffected by even the most powerful magnetic fields.
The blazar believed to have generated the neutrino – codenamed TXS 0506 + 056 – was located in less than a minute, after the IceCube team relayed coordinates for follow-up observations to telescopes worldwide. Being able to detect high energy neutrinos will provide yet another window on the universe, say the scientists. The sensational discovery of the second “messenger”, gravitational waves – ripples in space-time – was announced in February 2016.
France Cordova, director of the US National Science Foundation (NSF), that manages the IceCube laboratory, said: “The era of multimessenger astrophysics is here. “Each messenger, from electro-magnetic radiation [to] gravitational waves, and now neutrinos, gives us a more complete under-standing of the universe and important new insights into the most powerful objects and events in the sky.” Cosmic rays were discovered in 1912 by physicist Victor Hess, using instruments on a balloon flight. Later research showed them to be made of protons, electrons or atomic nuclei accelerated to speeds approaching that of light.