GRMHD simulations of magnetized advection-dominated accretion on a non-spinning black hole: role of outflows

Abstract

We present results from two long-duration general relativistic magneto-hydrodynamic (GRMHD) simulations of advection-dominated accretion around a non-spinning black hole. The first simulation was designed to avoid significant accumulation of magnetic flux around the black hole. This simulation was run for a time of 200 000 GM/c 3 and achieved inflow equilibrium out to a radius ∼90 GM/c 2 . Even at this relatively large radius, the mass outflow rateṀ out is found to be only 60 per cent of the net mass inflow rateṀ BH into the black hole. The second simulation was designed to achieve substantial magnetic flux accumulation around the black hole in a magnetically arrested disc. This simulation was run for a shorter time of 100 000 GM/c 3 . Nevertheless, because the mean radial velocity was several times larger than in the first simulation, it reached inflow equilibrium out to a radius ∼170 GM/c 2 . Here,Ṁ out becomes equal toṀ BH at r ∼ 160 GM/c 2 . Since the mass outflow rates in the two simulations do not show robust convergence with time, it is likely that the true outflow rates are lower than our estimates. The effect of black hole spin on mass outflow remains to be explored. Neither simulation shows strong evidence for convection, though a complete analysis including the effect of magnetic fields is left for the future.

An Accretion Disk-Outflow Model for Hysteretic State Transition in X-Ray Binaries

“…Our results can be compared to those of the MHD simulations on accretion disks (e.g., Igumenshchev et al 2003;Beckwith et al 2009;Penna et al 2010;Tchekhovskoy et al 2011;McKinney et al 2012;Narayan et al 2012). The magnetic pressure can dominate over the gas pressure in the inner region of the disk, and it becomes a magnetic arrested disk (Igumenshchev et al 2003).…”

“…The gas to magnetic pressure ratio β4 required in our analysis should be reasonable. The MHD simulations of magnetized ADAFs show that a large fraction of gas goes into the outflows, and the radial velocity of such ADAFs can be more than one order of magnitude higher than that of a self-similar ADAF (see Narayan et al 2012, for the details). In order to explain the observed hysteretic state transitions in XRBs, the radial velocity of an ADAF with outflows being up to ∼10 times higher than that of a conventional ADAF is required in some extreme state transition cases.…”

Kinetic and radiative power from optically thin accretion flows

“…By choosing a particular configuration of the initial seed magnetic field in the equilibrium torus, we chose to study accretion flows which are relatively weakly magnetized, and which do not lead to the saturation of the field at the BH horizon. The opposite limit would be the magnetically arrested disk (MAD, Narayan et al 2003), which shows properties dramatically different from the weakly magnetized state (SANE -using the nomenclature in Narayan et al 2012).…”

“…Initially, we performed a single, non-radiative, simulation with an equilibrium torus (same as in Narayan et al 2012) threaded by a magnetic field forming set of poloidal loops (again, same as in Narayan et al 2012, but flipping the polarity also across the equatorial plane) on a grid of 336 cells in radius and polar angle, and 32 cells in azimuth spanning π/2 wedge. Such a setup was evolved for 15000 t g , long enough for establishing a now-standard, scale-free solution of a thick and hot accretion flow with converged region extending up to ∼ 25R g .…”

Unstable mass-outflows in geometrically thick accretion flows around black holes

“…To explain the inflow-outflow rate versus radius relation, two types of models of the adiabatic inflow-outflow solution (Blandford & Begelman 1999Begelman 2012) Igumenshchev 2002) have been proposed. Furthermore, the recent hydrodynamical (HD) and magneto-hydrodynamical (MHD) simulations result in new findings of such outflows, winds and jets in the field of hot accretion flows around the black holes (Narayan et al 2012;Bu et al 2013;Li, Ostriker & Sunyaev 2013;Yuan et al 2015). The details of the geometrically thick hot accretion flows are referred to Yuan (2011) and Yuan & Narayan (2014).…”