Exploring the Role of Vector Potential and Plasma-$β$ in Jet Formation from Magnetized Accretion Flows

TL;DR

This study addresses how the initial magnetic field topology and plasma magnetization influence jet formation in magnetized accretion flows around black holes. Using GRMHD simulations with the HARM code in Kerr spacetime, it compares two vector-potential configurations $A_{}^{(1)}$ and $A_{}^{(2)}$ across three plasma-beta values $\beta\in\{50,100,500\}$ to track magnetic-flux accumulation, torus dynamics, and jet energetics. The results show that both configurations eventually reach the MAD state but on different timescales: $A_{}^{(1)}$ drives rapid flux advection and earlier jet launching, while $A_{}^{(2)}$ promotes a slower, disk-mediated buildup with a more ordered magnetic field and smoother jet structures; high-$\beta$ cases tend toward SANE-like behavior. These findings highlight the crucial role of initial magnetic topology in shaping early GRMHD evolution and offer practical guidance for seed-field choices in simulations and the interpretation of EHT-like observations of magnetically powered jets.

Abstract

In this work, we investigate how the choice of initial vector potential and plasma parameters influences the development of accretion columns and jet formation in magnetized accretion flows. Using general relativistic magnetohydrodynamic simulations, we explore two different configurations of the vector potential $A_φ$ and three plasma beta values $β$ = 50, 100, 500. We analyze how variations in the poloidal magnetic field strength and plasma magnetization affect magnetic flux accumulation near the black hole and the subsequent growth of the accretion column. Our results highlight the dependence of jet launching efficiency and accretion dynamics on the initial magnetic field topology and plasma beta, offering insight into the conditions that favor magnetically arrested disk or standard and normal evolution states.

Figures (9)

• Figure S1: Evolution of torus density ($\rho$) for $\beta = 50$ with the vector potential $A_{\phi}^{(1)}$ and spin parameter $a = 0.9$. The top row shows density along the poloidal plane $(\phi = 0)$ overlaid with magnetic field streamlines (white lines), while the bottom row shows the equatorial plane $(\theta = \pi/2)$ at times $t = 0$, $800$, $1700$, and $2600\,t_g$.
• Figure S2: Evolution of torus density ($\rho$) for $\beta = 100$ with the vector potential $A_{\phi}^{(1)}$ and spin parameter $a = 0.9$. The plot shows density along the poloidal plane $(\phi = 0)$ overlaid with magnetic field streamlines at times $t = 0$, $800$, $1700$, and $2600\,t_g$.
• Figure S3: Evolution of torus density ($\rho$) for $\beta = 50$ with the vector potential $A_{\phi}^{(2)}$ and spin parameter $a = 0.935$. The plot shows density along the poloidal plane $(\phi = 0)$ overlaid with magnetic field streamlines at times $t = 0$, $800$, $1300$, and $1800\,t_g$.
• Figure S4: Evolution of torus density ($\rho$) for $\beta = 100$ with the vector potential $A_{\phi}^{(2)}$ and spin parameter $a = 0.935$. The plot shows density along the poloidal plane $(\phi = 0)$ overlaid with magnetic field streamlines at times $t = 0$, $800$, $1300$, and $1800\,t_g$.
• Figure S5: Snapshots at $t = 1800$ showing the spatial distributions of key quantities for the two magnetic configurations. The left and right columns correspond to $A_{\phi}^{(1)}$ and $A_{\phi}^{(2)}$, respectively in each quantity. The three panels in each row show (from left to right) the density, plasma $\beta$, and magnetization parameter $\sigma$. The top row corresponds to an initial plasma $\beta = 50$, and the bottom row to $\beta = 100$. White streamlines trace the poloidal magnetic field lines, illustrating the magnetic topology and its evolution in each configuration.