Black Hole Accretion with Saturated Magnetic Pressure and Disk Wind

Abstract

We construct an analytical black hole accretion disk model that incorporates both magnetic pressure and disk wind, which are found to be important from numerical simulations. A saturated magnetic pressure that relates the Alfvén velocity with local Keplerian velocity and gas sound speed is assumed in addition to radiation and gas pressures. The mass accretion rate is assumed to have a power-law form in response to mass loss in the wind. We find three sets of self-consistent solutions that are thermally stable and satisfy the model assumptions. At high accretion rates, the disk is geometrically and optically thick, resembling the slim disk solution. At relatively low accretion rates, our model predicts an accretion flow consisting of a geometrically thin and optically thick outer disk (similar to the standard disk), and a geometrically thick and optically thin inner disk (similar to the advection-dominated accretion flow, or ADAF). Thus, this is a natural solution for a truncated disk connected with an inner ADAF, which has been proposed to explain some observations. The magnetic pressure plays a more important role than the outflow in shaping the disk structure. The observed disk luminosity tends to saturate around 8 times the Eddington limit, suggesting that supercritical accretion onto black holes can be used for a black hole mass estimate, or a standard candle with known black hole masses.

Magnetized Accretion Disks with Outflows for Changing-look AGNs

“…The effects of magnetic fields on accretion disks have been extensively studied, and some early research (Ferreira & Pelletier 1995;Ferreira 1997;Jacquemin-Ide et al 2019;Huang et al 2023b) found that magnetic winds can significantly decrease the accretion timescale. This finding has been confirmed by numerical simulations (Jacquemin-Ide et al 2021;Scepi et al 2023) and has been used to explain observed phenomena such as young stellar objects (Combet & Ferreira 2008;Martel & Lesur 2022) and X-ray binaries (Ferreira et al 2006;Marcel et al 2018).…”

The First Polarimetric View on Quasiperiodic Oscillations in a Black Hole X-Ray Binary

“…One class attributes QPO to geometric effects, with the Lense-Thirring precession model of the inner flow being one of the most popular in this category. Initially proposed by Stella & Vietri (1998), this model was further developed by Ingram et al (2009), considering a precessing accretion flow within a truncated accretion disk (Esin et al 1997;Huang et al 2023). While successfully applied to some sources for explaining QPO properties, Nathan et al (2022) recently discovered a very small truncated radius in GRS 1915+105, which does not match the prediction of this model.…”