Maximal spin and energy conversion efficiency in a symbiotic system of black hole, disc and jet

Abstract

We study a combined model of black hole-accretion disc-magnetosphere-jet symbiosis, applicable for supermassive black holes. We quantify the mass and spin evolution and analyse how the limiting value of the spin parameter and the conversion efficiency of accreted mass into radiation depend on the interplay of the electromagnetic radiation reaction, magnetosphere characteristics and truncation radius of radiation. The dominant effect comes from the closed magnetic field line region, which reduces the spin limit to values ~0.89 (instead ~0.99 in its absence). Therefore, observations on black hole spins could favour or disfavour the existence of the closed magnetic field line region (or its coupling to the disc). We also find that the suppression of radiation from the innermost part of the accretion disc, inferred from observations, and a collimated jet both increase the spin limit and the energy conversion efficiency. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.