Launching proton-dominated jets from accreting Kerr Black Holes: the case of M87

Abstract

A general relativistic model for the formation and acceleration of low mass-loaded jets from systems containing accreting black holes is presented. The model is based on previous numerical results and theoretical studies in the Newtonian regime, but modified to include the effects of space-time curvature in the vicinity of the event horizon of a spinning black hole. It is argued that the boundary layer between the Keplerian accretion disk and the event horizon is best suited for the formation and acceleration of the accretion-powered jets in active galactic nuclei and micro-quasars. The model presented here is based on matching the solutions of three different regions: i- a weakly magnetized Keplerian accretion disk in the outer part, where the transport of angular momentum is mediated through the magentorotational instability, ii- a strongly magnetized, advection-dominated and turbulent-free boundary layer (BL) between the outer cold accretion disk and the event horizon and where the plasma rotates sub-Keplerian and iii- a transition zone (TZ) between the BL and the overlying corona, where the electrons and protons are thermally uncoupled, highly dissipative and rotate super-Keplerian. In the BL, the gravitation-driven dynamical collapse of the plasma increases the strength of the poloidal magnetic field (PMF) significantly, subsequently suppressing the generation and dissipation of turbulence and turning off the primary source of heating. In this case, the BL appears much fainter than standard disk models so as if the disk truncates at a certain radius. The action of the PMF in the BL is to initiate torsional Alf`ven waves that transport angular momentum from the embedded plasma vertically into the TZ, where a significant fraction of the shear-generated toroidal magnetic field reconnects, thereby heating the protons up to the virial-temperature. Also, the strong PMF forces the electrons to cool rapidly, giving rise therefore to the formation of a gravitationally unbound two-temperature proton-dominated outflow. Our model predicts the known correlation between the Lorentz-factor and the spin parameter of the BH. It also shows that the effective surface of the BL, through which the baryons flow into the TZ, shrinks with increasing the spin parameter, implying therefore that low mass-loaded jets most likely originate from around Kerr black holes. When applying our model to the jet in the elliptical galaxy M87, we find a spin parameter a ∈ [0.99, 0.998], a transition radius rtr ≈ 30 gravitational radii and a fraction of 0.05 − 0.1 of the mass accretion rate goes into the TZ, where the plasma speeds up its outward-oriented motion to reach a Lorentz factor Γ ∈ [2.5, 5.0] at rtr.

On the viability of gravitational Bose-Einstein condensates as alternatives to supermassive black holes

“…However, this rotational frequency is too low to explain the origin of power of highly collimated jets observed in microquasars, high‐redshifted quasars as well as at the centre of active galaxies. These are considered to originate from the vicinity of fast spinning BHs, where direct extraction of rotational energy from the BH via Blandford–Znajek mechanism or from the boundary layer (BL) via dynamo action is considered to be most efficient (see Blandford & Znajek 1977; Brezinski & Hujeirat 2011, and references therein). Consequently, unless SMBECs are born massive, their cosmological growth will normally be associated with an increase of their rotational energy, which would enforce the cores to rotate at a much higher speed than the above estimated value.…”

“…5 shows that Γ is highly sensitive to α 0 , indicating therefore that large Γ factors between 10 and 20 may be obtained if the jet velocity is a significant fraction of the escape velocity. Equivalently, the jet plasma must start its outward‐oriented motion either from the very vicinity of the object’s surface or from nearby the event horizon. We note that the formation and acceleration of jet plasmas around accreting relativistic objects is considered to be the outcome of complicated coupling processes between the accretion disc, the central object and the jet plasma, whereby magnetic fields play a crucial role (Hujeirat 2004; Brezinski & Hujeirat 2011). Jets emanating from around surface‐free objects are generally observed to be radio‐dominated and their plasmas propagate with larger Lorentz factors compared to those of neutron stars.…”

“…We note that the formation and acceleration of jet plasmas around accreting relativistic objects is considered to be the outcome of complicated coupling processes between the accretion disc, the central object and the jet plasma, whereby magnetic fields play a crucial role (Hujeirat 2004; Brezinski & Hujeirat 2011). Jets emanating from around surface‐free objects are generally observed to be radio‐dominated and their plasmas propagate with larger Lorentz factors compared to those of neutron stars.…”