The keys by Nikolai Kardashev and Yuri Parijskij to the Nature of Active Galactic Nuclei

The Joint AGN Research Observing Program of IKI RAS/ASC FIAN and SAO RAS has been carried out at RATAN-600 since April 1979 thanks to the initiative of Nikolai Kardashev and the constant support of Yuri Parijskij (“Key-1”). The main task is to study active galactic nuclei (AGNs) based on RATAN-600 surveys and monitoring of instantaneous 1–22 GHz spectra of AGNs. The “Hedgehog” model of AGNs was proposed in 1969 by N. S. Kardashev and developed in the works of a number of authors (“Key-2”). The report summarizes the main observed properties of AGNs obtained in the Program based on the RATAN-600 instantaneous spectra for a large sample of extragalactic objects with VLBI compact components. It is shown that the 6-frequency RATAN-600 1-22 GHz spectra and their long-term variability are consistent with the Hedgehog model for a relativistic jet of electrons and protons in the strong longitudinal magnetic field from an AGN nucleus. The RATAN-600 spectral support of ground-space VLBI has been performed for the projects VSOP (1997–2003) and RadioAstron (2011–2019) including a study of many AGNs with the RadioAstron detections of super-high brightness temperatures up to 10 14 K, “Key-3”). Since 2020, the work has been supplemented by a new topic of multichannel astronomy, “radio-neutrino” (“Key-4”), the current results of which show that the earlier role of the synchrotron radio emitting protons in the strong magnetic field of the jet could be underestimated in AGN astrophysics. New data of this topic will test this hypothesis.