Advances in the knowledge of the universal accretion phenomenon and jet physics, are important not only for astrophysics of stellar-size systems in our Galaxy like cataclysmic variable stars and active galactic nuclei (AGNs), but could be able to contribute to some contemporary multi-messenger and astro-particle research topics.
Astrophysical accretion and binary systems are undoubtedly useful, especially in the case of outflows and production of jets, to understand the role of gravitation in producing high-energy, X-ray and gamma-ray, emission, gravitational waves, accelerated very/ultra-high-energy neutrinos and cosmic rays. In particular close and spatially-unresolved gravitationally bound binaries of supermassive black holes (SMBHs) in AGN are expected to induce cyclical modulations and outbursts in the emitted electromagnetic flux and to produce micro/nano-Hz frequency gravitational waves.
The first discovery of a very high energy neutrino from a flaring GeV gamma-ray blazar
and theoretical predictions about the possibility of accreting black holes with gravitationally bound axion-like particle clouds subject to superradiance, are pointing out AGN and blazars as cosmic beacons able to represent also optimal cosmic laboratories for gravitation and high-energy particle physics. In this frame some developments on the last observational results about a famous radio/gamma-loud, jetted, blazar OJ 287, that is expected to harbor a binary SMBH system are here summarized.