Evidence for magnetically arrested accretion disks across the black hole mass scale

© Eric Clausen-Brown (MPIfR)

Black hole accretion disk models typically assume that the magnetic field pressure is much less than the plasma pressure. However, simulations that include an abundance of poloidal magnetic flux threading the disk find that this flux is transported inwards until the magnetic pressure reaches an equilibrium with the ram pressure of the accreting plasma. At this point a "magnetically arrested disk" is formed where the magnetic pressure is well above the plasma pressure. The resulting equilibrium magnetic flux threading the hole then remains somewhat steady, and is proportional to the product of black hole mass with the square root of the accretion rate.

We test this magnetically arrested disk scenario in a sample of radio-loud blazars and radio galaxies, and find a good agreement between the accretion rate of these sources and the poloidal magnetic flux threading their central black holes. The accretion rate and black hole magnetic flux for a given source are determined by the inferred accretion luminosity and the VLBI coreshift effect, respectively.

We have also conducted a similar analysis for two jetted XRBs and for the galactic center, with encouraging results. The implications of our work with regard to jet power and the radio loud/quiet dichotomy will be discussed.