University of São Paulo: Computer simulation reveals how “particle accelerators” in black holes produce cosmic rays

Particle accelerators are built on Earth to research physical phenomena, concentrating large amounts of energy to move particles smaller than the atom at extremely high speeds and observe their behavior. In space, there are also particle accelerators, in the form of jets of gas emanating from black holes. They are capable of accelerating particles to very high energies that travel at speeds close to that of light, called cosmic rays. At USP’s Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG), research used computer simulations to understand how jets work and how they accelerate particles, revealing that the energy involved in their formation is among the most extreme produced in the Universe, far superior to that produced in human-made particle accelerators.

The results of the work are described in two articles published in the Astrophysical Journal, in February and May 2021. “Galaxies and their cores containing black holes and jets are the ‘bricks’ that make up even larger structures in the Universe, which they are the clusters of galaxies”, says Professor Elisabete de Gouveia Dal Pino, from IAG, who coordinated the study.

“Understanding how these nuclei and jets form and emanate from the centers of these galaxies helps us understand not only their formation and evolution process, but also that of galaxy clusters, helping us to better understand the physical processes that happen around them. of black holes.”

Thus, the research sought to identify the origin of extreme energy cosmic rays (UHERCRs, acronym for ultra-high-energy cosmic rays ) in relativistic jets, which are gas ejections of charged particles permeated by magnetic fields, produced by the holes. black. “Most galaxies have at their core, that is, at their center, supermassive black holes, with masses from millions to billions of times greater than the mass of the Sun,” he says. “The Milky Way, which is our galaxy, for example, hosts at its core a black hole considered small, 2 million times the mass of the Sun.”

The jets emanating from galaxies with supermassive black holes, called active galaxies, are called relativistic because they move at a speed close to the speed of light, says the professor. “The research also tried to explain the mysteries that involve the emission of gamma rays and also of neutrinos, particles smaller than the atom that these sources produce through cosmic rays”, she reports. “To model these jets, we performed high-performance numerical simulations on our computer cluster , which reconstruct the evolution of a jet.”

particle acceleration
To simulate the jets and the production of cosmic rays, low-energy particles (protons) were injected, which were then accelerated into the jet by a mechanism called magnetic reconnection. “The particles are exponentially accelerated to energies from 1016 to 1020 electron volts, which are among the most extreme in the Universe”, describes Elisabete Dal Pino. “These simulations correspond to ultra-high-energy cosmic rays detected by the Pierre Auger Observatory, located in Mendoza, Argentina.”

The experiments demonstrated that only through astrophysical sources it is possible to accelerate particles with such high energies. “To give you an idea, the largest accelerators on Earth, installed in the laboratory of the European Organization for Nuclear Research (Cern), in Switzerland, accelerate particles to a maximum of 1013 electron volts, that is, although there are other potentially astrophysical sources capable, the relativistic jets of black holes are one of these ‘cosmic particle accelerators’”, emphasizes the professor.

The researchers now reconstruct the entire flow of radiation and neutrinos produced by ultra-high-energy cosmic rays in active galaxies.

“In particular, we are reproducing the flow observed in the active galaxy TXS 0506+056, also called Blazar”, reports the scientist. “This source galaxy became famous in 2018 with the discovery by the IceCube observatory, located in Antarctica, and several gamma-ray observatories, of the simultaneous direct emission of neutrinos and gamma rays for the first time in an astrophysical source, which evidenced the presence of ultra-high-energy cosmic rays in relativistic jets.”

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