Evolution of MHD Torus and Mass Outflow Around Spinning AGN

Mohammed Ramiz Aktar^1*, Kuo-Chuan Pan^1,2,3, Toru Okuda⁴

¹Department of Physics and Institute of Astronomy, National Tsing Hua University, Hsinchu City, Taiwan
²Center for Theory and Computation, National Tsing Hua University, Hsinchu City, Taiwan
³Physics Division, National Center for Theoretical Sciences, National Taiwan University, Taipei, Taiwan
⁴Hakodate Campus, Hokkaido University of Education, Hakodate 040-8567, Japan

* Presenter:Mohammed Ramiz Aktar, email:ramizaktar@gmail.com

We present axisymmetric, two-dimensional magnetohydrodynamic (MHD) simulations to investigate accretion-ejection mechanisms around spinning AGN. To mimic the space-time geometry of spinning black holes, we consider effective Kerr potential. We initialize the accretion disc with a magnetized torus by adopting the toroidal component of the magnetic vector potential. The initial magnetic field strength is set by using the plasma beta parameter ($\beta_0$). We observe self-consistent turbulence generated by magneto rotational instability (MRI) in the disc. The MRI turbulence transports angular momentum in the disc, resulting in an angular momentum distribution that approaches a Keplerian distribution. We investigate the effect of the magnetic field on the dynamics of the torus and associated mass outflow from the disc around a maximally spinning black hole $(a_k = 0.99)$. Interestingly, we observe that the high magnetic model $\beta_0 = 10$ belongs to the ``magnetically arrested disk (MAD)'' state, and all the other low magnetic models remain in the SANE state. We observe that mass outflow rates are significantly enhanced with the increased magnetic field in the disc. We find a positive correlation between the magnetic field and mass outflow rates. We also investigate the effect of black hole spin on the magnetized torus evolution. However, we have not found any significant effect of black hole spin on mass outflows in our model. Finally, we discuss the possible astrophysical applications of our simulation results.

Keywords: accretion, accretion discs, black hole physics , (magnetohydrodynamics) MHD, ISM: jets and outflows, quasars: supermassive black holes