A Black Hole Manifesto

Abstract

A brief overview is presented of some aspects of the study of thegrowth of massive black holes in active galactic nuclei. It is arguedthat relativistic effects described by the Kerr solution of a spinningblack hole are essential and are responsible for the formation ofrelativistic jets. It is further asserted that when the mass accretionrate is much larger and much smaller than the Eddington rate, theaccretion is adiabatic and accompanied by prodigious outflows,ultimately driven by the energy flow through the disk associated withthe magnetic torque. It is conjectured that this torque is dictated bythe magnetic conditions at large radius and that, typically, there ispreferred radial polarity in the magnetic field that joins the diskalong with freshly accreted gas at its outer boundary. The associatedmagnetic flux is concentrated by the inflowing gas and soon becomesdynamically dominant so that it escapes the disk, driving an MHD wind.The radial field persists all the way down to the event horizon of theblack hole and supplies a large flux to the hole when the disk isthick. Consequently, rapidly spinning holes accreting rapidly or slowlyshould be accompanied by relativistic jets which spin down the hole.The disks associated with intermediate accretion rates should berelatively thin and spin up the hole without forming powerful jets.This model provides a qualitative interpretation of the observedcosmological evolution of AGN, whereby the black holes that form later,lose the competition with star formation and grow to smaller masses.The co-evolution of black holes and their host galaxies is brieflydiscussed along with the impact on the intergalactic medium.