Particle acceleration in the Centaurus A localized

Enlarge imageSuperposition of the Emission to Centaurus A in different wavelength ranges. The light blue Ellipse describes the emission model of Centaurus A in a high-energy gamma radiation, as it was calculated from the H. E. S. S. scientists.
(Image: CNRS)

Radio galaxies belong to the class of galaxies with an active and bright center, from the huge, directed matter flows are ejected, referred to as Jets. As a source of energy of these Jets of extremely mass-presumed Black holes with the mass of a hundred million to a few billion solar masses. Jets from active galaxies can be explained by the nuclei due to the incidence of matter on such a super massive black hole. You throw particle flows with speeds close to the speed of light over hundreds to thousands of light years far into space. Due to the large distance to these objects, their structures can be resolved, but only for the next of them.

In the case of the – on astronomical scales – only about 12 million light-years away in the radio galaxy Centaurus A, one of the brightest galaxies in the southern sky, was measured in the Jet so far, from radio to x-ray energies. „At the high energy end of the electromagnetic spectrum of Centaurus A could be previously observed only as an unresolved point source,“ explains Dr. Markus Holler from the Institute for Astro – and particle physics of the University of Innsbruck and a member of the H. E. S. S. collaboration. Whether the high-energy gamma radiation from the galaxy core, or is emitted from the Jet, one could not, therefore, found to date. Here, an important contribution of Innsbruck, Astro-physicist, for the collaborative study on: How recently the successful Measurement of the crab nebula, the scientists used scientists from the research group of Univ.-Prof. Olaf Reimer for the study of the structures of Centaurus a, a novel simulation environment. This allowed a much more precise analysis of a total of over 200 hours of observation time with the H. E. S. S. telescopes.

„The simulations that we needed for the evaluation, are typically generated prior to the observations. In our simulation environment, but there are for each observation in the analysis, a tailor-made Simulation,“ explains astrophysicist Markus Holler. So, it is managed to high-energy gamma radiation along the Jets of Centaurus A demonstrate. „So, we can not distinguish, only for the first time, Centaurus A from a point source, but even the Emission of the shape of this part of the Jet mapping.” The measured expansion of the Jets of about 2 angular minutes (see figure) in the gamma-ray light reveals an exciting secret: Namely, the answer to the question of where and how the high-energy gamma radiation from Centaurus A is formed.

Conclusions on particle acceleration in the Jet
Taking into account the other measuring instruments – v. a. Radio and x-ray observations – derived information on Centaurus A, as well as the H. E. S. S. measured Emission of the Jets in a model, so the latter can only be achieved with an extremely efficient, along with the Jets distributed, continuously-operating accelerating mechanism to explain it. „The mere fact that photons from the Jet radiation up in these high-energy gamma range were detected, requires the existence of charged particles, the need to achieve a power of at least 10 to 100 trillion electron volts,” says the theorist Prof. Anita Reimer from the Institute for Astro – and particle physics, University of Innsbruck, a Central result of the study. „The extent to which similar efficient particle acceleration is not in the vast Jetbereichen also a characteristic of other active galactic nuclei, which are distinguished by extreme radio brightness, such as Centaurus A, is a question that should be answered by the future Cherenkov Telescope Array (CTA),” Prof., Olaf Reimer, who coordinates the Austrian participation in the preparation and construction of the highest-energy gamma-ray Observatory CTA. If Centaurus A can be seen as generic for many more galaxies are considered, it will show in other research projects.

Indirect measurement of gamma radiation
The H. E. S. S. telescopes are named after the discoverer of cosmic rays and Nobel prize winner Victor Franz Hess, who was from 1931 to 1937 as a Professor at the University of Innsbruck, Austria. You can measure gamma rays, which are about 1,000 billion Times more energetic than visible light. Each of these Gamma-quanta produced when hitting the earth’s atmosphere, among other things, a variety of charged particles, which emit in turn, through the Cherenkov effect (a kind of optical analogue to the Sonic boom) visible light. The H. E. S. S. telescopes are operated since 2002 by an international collaboration in Namibia. Since 2009 Austria is a member, Olaf Reimer from the Institute for Astro – and particle physics, University of Innsbruck, the Austrian H. E. S. S. group.

The H. E. S. S. Collaboration: “Resolving acceleration to very high energies along the Jet of Centaurus A”
DOI: 10.1038/s41586-020-2354-1



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