Most cosmic rays, though, have an electrical charge, and their paths get bent by the magnetic fields scattered throughout space, making it difficult to follow their footsteps home. Since then, scientists have been hunting for the astrophysical accelerators responsible for hurling the most tremendously energetic of these particles across the cosmos. In the early 1900s, physicist Victor Hess discovered that Earth is being constantly bombarded by energetic particles coming from outer space, which we now call cosmic rays. The analysis of ANTARES has been submitted to the journal Astrophysical Journal Letters and appears on arXiv.A flash of light detected about a mile below the South Pole likely solves a century-old cosmic mystery-and potentially opens up a new kind of astronomy involving ghostly subatomic particles called neutrinos. ‘From that period we found one neutrino coming from the direction of the blazar, but that is too little to draw conclusions on,’ says Samtleben. ANTARES is less susceptible to the part of the sky where the blazar can be found.’ The team also did a targeted search through the data of the period 2007-2017. ‘IceCube is on the South Pole, we are on the Northern Hemisphere. ANTARES did not find a neutrino signal from the direction of the blazar that day. Samtleben and her colleagues reviewed their ANTARES data for September 22 nd 2017. This is also promising news for KM3NeT (successor of ANTARES, ed.), because we expect these signals to be evenly distributed across the sky.’ Review It is the first time that a cosmic neutrino has been traced back to its source in a distant galaxy. She is pleased with the discovery: ‘This is an important milestone for neutrino science. Dorothea Samtleben coordinates the search for cosmic sources at ANTARES. Researchers from ANTARES, the neutrino detector in the Mediterranean Sea, helped out in the quest. A second analysis, also in Science, shows that neutrinos previously detected by IceCube originate from the same source. Scientists from the eighteen involved observatories present their results in Science. Through a dragnet of telescopes on Earth and in space, scientists subsequently found the source: a supermassive black hole at about four billion lightyears, in the Orion constellation, which serves as a natural particle accelerator.

On September 22 nd 2017, such a neutrino hit IceCube, on Antarctica. If one accidentally strikes Earth, we can derive from its direction where cosmic radiation comes from. According to particle physics theory, high-energy neutrinos are produced simultaneously with cosmic radiation, and because they barely interact with the world around them, they fly right through the Universe in a straight line. Fortunately, ultra-lightweight particles called neutrinos might come to the rescue. So it remains a mystery which direction they actually come from. During their long journey through the Universe of sometimes billions of lightyears, they are deflected within all kinds of magnetic fields. For decades, we have been detecting high-energetic particles that are bombarding Earth from space. One of the big questions in science is where cosmic rays come from.

Neutrino radiation