Neutrinos are ghostly subatomic particles that can travel for billions of light years from the most extreme environments in the universe to reach even the Earth. The observations were made by the IceCube Neutrino Observatory at the Amundsen–Scott South Pole Station and confirmed by telescopes around the globe. Since they were first detected over one hundred years ago, cosmic rays – high-energy particles that continuously rain down on Earth from space – have posed an enduring mystery. What creates these particles and how can they travel unhindered across such vast distances? Where do they come from?
Two articles in Science
Two papers published this week (13 July 2018) in the journal Science have for the first time provided evidence for a known blazar as the source of some of the high-energy neutrinos detected. A blazar is a supermassive black hole at the centre of an active giant elliptical galaxy.
Two gamma-ray observatories – NASA’s Fermi Space Telescope and the Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC) in the Canary Islands, have detected a flare of high-energy gamma rays associated with the black hole concerned. Nick van Eijndhoven: "These observations convincingly implicate the blazar as the most likely source."
Bolstering these observations are coincidental measurements from other instruments, including optical, radio, and X-ray telescopes.
A mystery dating back to 1912
The Austrian physicist Victor Hess proved in 1912 that the ionizing particles scientists were detecting in the atmosphere originated in space. Cosmic rays are the highest energy particles ever observed, with energy levels of up to a hundred million times those of particles in the Large Hadron Collider at CERN in Switzerland, the most powerful human-made particle accelerator. These extremely high-energy cosmic rays can only be created outside our galaxy, and their sources have remained a mystery until now. Scientists had speculated that the most violent objects in the cosmos, things like supernova remnants, colliding galaxies, the mysterious gamma-ray bursts, and the energetic black hole cores of galaxies known as active galactic nuclei, such as blazars, could be the sources.
IceCube at the South Pole
Detecting the highest energy neutrinos requires a massive particle detector, and IceCube is the world’s largest by volume. Encompassing a cubic kilometre of deep, pristine ice a mile beneath the surface at the South Pole, the detector is composed of more than 5,000 light sensors arranged in a grid.
The IceCube Collaboration, with over 300 scientists in 49 institutions around the world, runs an extensive scientific program that has established the foundations of neutrino astronomy. Their research efforts, including critical contributions to the detector operation, are financed by funding agencies in Australia, Belgium, Canada, Denmark, Germany, Japan, New Zealand, Republic of Korea, Sweden, Switzerland, the United Kingdom, and the U.S. https://icecube.wisc.edu/collaboration/institutions
Around 20 observatories on Earth and in space have participated in the identification of what scientists deem to be a source of very high-energy neutrinos and thus of cosmic rays. The journal also contains papers on various follow-up observations.
Nick van Eijndhoven: “With this new breakthrough, which follows on the detection of cosmic high-energy neutrinos in 2013, IceCube has genuinely made neutrino astronomy possible."
Interuniversity Institute for High Energies
The Brussels-based Interuniversity Institute for High Energies (IIHE), a joint institute of the Université Libre de Bruxelles (ULB) and Vrije Universiteit Brussel (VUB), hosts one of Europe's main IceCube analysis centres. The Brussels team is heavily involved in the search for high-energy neutrinos originating from gamma-ray bursts and active galactic nuclei. The IceCube team at the IIHE consists of members from both the Université Libre de Bruxelles (ULB) and the Vrije Universiteit Brussel (VUB).
The IceCube research efforts in Brussels have been made possible by the financial support of the FNS-FNRS and FWO-Vlaanderen scientific research funds, the FWO Odysseus program, the Belgian Federal Science Policy Office (Belspo) and the Flanders Agency for Innovation in Science and Technology (IWT). According to Willy Verstraete, President of the FWO: “The FWO attaches great importance to funding for large international research facilities. Since 2000, the FWO has invested seven million Euros in the IceCube international research project. In this way, Flanders has made a substantial contribution to this important discovery."
Find out more
Nick van Eijndhoven, 0032 (0)488.074166, Nick.van.Eijndhoven@vub.ac.be
In the beginning there was nothing, which exploded.