NASA’s Fermi Mission Identifies Black Hole that Launched a Cosmic Neutrino
About 4 billion years ago, a super-massive black hole in the heart of a distant galaxy erupted a stream of extremely energetic particles in the direction of Earth. Now, an international team of researchers, including also a researcher from University of Nova Gorica, has revealed how one of these particles, elusive neutrinos, was detected and, with the help of NASA’s Fermi Gamma-ray Space Telescope, linked back to its likely source.
This is the first time that we have a direct indication that astrophysical sources called blazars, or rather the super massive black holes that lie in their centers, are the power engines capable of accelerating neutrinos to energies up to million times their mass, much larger than anything we can produce at Earth.
Since they were first detected over one hundred years ago, cosmic rays - highly energetic particles that continuously rain down on Earth from space - have posed an enduring mystery: What are the sources capable of launching particles with the extreme energies across such vast distances? Where do they come from?
Because cosmic rays are charged particles, their paths cannot be traced directly back to their sources due to the powerful magnetic fields that fill space and warp their trajectories. But the cosmic accelerators that produce cosmic rays, will also produce neutrinos and photons (or light). Neutrinos and photons (among which gamma rays are the most energetic form of light) are uncharged particles and unaffected by even the most powerful magnetic field, they travel nearly undisturbed from their accelerators, giving scientists an almost direct pointer to their source.
Thanks to the rapid increase in the number of large-scale astrophysical experiments at the beginning of the XXI century, the astrophysical community finally got the much-needed tools to answer the question about the origin of cosmic rays. The indirect evidence that astrophysical sources called blazars, or more precisely, violent environments surrounding super massive black holes that lay at their centers, could be the power engines capable of producing the most energetic cosmic rays we detect at the Earth, was building over the years.
Thanks to the international team of scientists, which worked closely across different high-energy astrophysics experiments, we finally might have the first direct proof of this conjecture! The paper published in Science July 12th presents the first evidence of a match between the source position of a high-energy cosmic neutrino, as measured by the IceCube experiment, with a known gamma-ray blazar TXS 0506+056, which is currently in its active state (as first noticed by the Fermi LAT collaboration, in which Dr. Gabrijela Zaharijas from University of Nova Gorica participates), and then confirmed with many observatories around the globe.
“Today we are announcing that Fermi’s gamma-ray eyes have detected light from the same distant galaxy from which a high energy neutrino was detected,” said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington. “This is another giant leap in the growing field of multi-messenger astronomy, following Fermi’s detection last year of light connected to a gravitational-wave event caused by the merging of two neutron stars.”
This coincidence of the detection with two different cosmic ray messengers (energetic photons and neutrinos) singles out the blazar as the source of this most energetic neutrino emission and sheds further light on details of the physics mechanisms happening in the vicinity of the black holes.
More information in the science article: "http://science.sciencemag.org/cgi/doi/10.1126/science.aat1378"
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