For the first time, scientists have been able to pinpoint a source of neutrinos outside of our galaxy. The extremely light and nigh-invisible elementary particle spotted by scientists has originated in the TXS0506+56 galaxy – a blazar – as evidenced by gamma ray observations.
Nearly a year ago, the IceCube Neutrino Observatory – a neutrino detector built deep within the ice of the Antarctic on the grounds of the Amundsen-Scott South Pole Station – identified a high energy neutrino of possibly cosmic origin. Similarly to several dozen discovered before, this single neutrino wasn’t enough to identify its source, as it doesn’t provide the required amount of data.
The difficulty in observing neutrinos comes from the fact that they have no electric charge, and their mass is over a million times smaller than that of an electron. Additionally, their interaction with matter is very weak. These properties have earned them the nickname of ‘ghost particles’.
After the neutrino was discovered, scientists began to monitor the ‘suspicious’ part of the heavens with a number of telescopes registering various types of radiation. Four hours after the IceCube staff asked for help, several other research centres joined them in observing high energy gamma radiation. The first was H.E.S.S. Observatory in Namibia, followed by VERITAS Observatory in Arizona (USA) and MAGIC Observatory (Canary Islands, Spain).
During these observations, a shining object appeared – the TXS0506+56 galaxy, identified as the possible source of both the gamma radiation and the neutrinos.
Blazar – a source of neutrinos
TXS 0506+56 is located approximately four billion light years away from Earth. It’s a blazar – a type of an active galaxy. Most of the high amounts of energy radiated out by active galaxies comes from their centrally-positioned supermassive black holes. Thanks totheir incredibly strong gravity, they attract vast amounts of matter, which in turn causes streams of matter and magnetic fields to flow out of its proximity with a speed that’s close to the speed of light.
In case of blazars, this ‘outward flow’ (called a relativistic jet) is directed very nearly towards the Earth (as opposed being directed some other way) – this makes them appear much brighter than they would otherwise be. Examining gamma radiation is not sufficient to determine if it’s composed of electrons or protons and nuclei. However, neutrinos are indeed traces of accelerated protons or even nuclei: the latter ones collide with interstellar medium particles and create pions (unstable elementary particles) that degrade and emit neutrinos.
Observing gamma radiation together with neutrinos is fascinating, since their formation must be related to accelerating protons or nuclei to high speeds (i.e. energies). These high energy protons and nuclei are part of the cosmic rays, the origins of which have been a mystery for scientists since their discovery one hundred years ago. This directly proves that blazars contain cosmic particle accelerators.
This is a tremendous success and a major breakthrough for the newly developing branch of neutrino astronomy, especially because the project used various types of data to corroborate one another. These include observations of electromagnetic spectrum, electromagnetic waves, neutrinos, cosmic rays, and gravitational waves.
The results of these observations were described by JU Astronomical Observatory researchers – Prof. Michał Ostrowski, Dr hab. Marek Jamrozy, Natalia Żywucka-Hejzner and Angel Priyama Noel in an article entitled Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A, which was published in Science on 13 July 2018.
Original text: www.nauka.uj.edu.pl