Constraints on the Evolution of Black Hole Spin due to Magnetohydrodynamic Accretion

Abstract

Stationary and axisymmetric ideal magnetohydrodynamic (MHD) accretion onto a black hole is studied analytically. The accreting plasma ejected from a plasma source with low velocity must be super-fast magnetosonic before passing through the event horizon. We work out and apply a trans-fast magnetosonic solution without the detailed analysis of the regularity conditions at the magnetosonic point, by introducing the bending angle $\beta$ of magnetic field line, which is the ratio of the toroidal and poloidal components of the magnetic field. To accrete onto a black hole, the trans-magnetosonic solution has some restrictions on $\beta$, which are related to the field-aligned parameters of the MHD flows. One of the restrictions gives the boundary condition at the event horizon for the inclination of a magnetic field line. We find that this inclination is related to the energy and angular momentum transport to the black hole. Then, we discuss the spin-up/down process of a rotating black hole by cold MHD inflows in a secular evolution timescale. There are two asymptotic states for the spin evolution. One is that the angular velocity of the black hole approaches to that of the magnetic field line, and the other is that the spin-up effect by the positive angular momentum influx and the spin-down effect by the energy influx (as the mass-energy influx) are canceled. We also show that the MHD inflows prevents the evolution to the maximally rotating black hole.

16 pages, 12 figures, submitted to PRD

References in corpus (15)

• General Relativistic Magnetohydrodynamic Simulations of Jet Formation and Large-Scale Propagation from Black Hole Accretion Systems
• A Measurement of the Electromagnetic Luminosity of a Kerr Black Hole
• Efficiency of Magnetized Thin Accretion Disks in the Kerr Metric
• Magnetically Driven Accretion Flows in the Kerr Metric II: Structure of the Magnetic Field
• General Relativistic Simulations of Jet Formation in a Rapidly Rotating Black Hole Magnetosphere
• Accretion Disk Torqued by a Black Hole
• Force-Free Magnetosphere of an Accretion Disk -- Black Hole System. II. Kerr Geometry
• Theory and astrophysical consequences of a magnetized torus around a rapidly rotating black hole
• Magnetically-Dominated Accretion Flows (MDAFs) and Jet Production in the Low/Hard STate
• Force-Free Magnetosphere of an Accretion Disk -- Black Hole System. I. Schwarzschild Geometry
• The structure of black hole magnetospheres. I. Schwarzschild black holes
• Relativistic Acceleration of Magnetically Driven Jets
• Black Hole Magnetospheres Around Thin Disks Driving Inward and Outward Winds
• Trans-Magnetosonic Accretion in a Black Hole Magnetosphere
• Energetics of Black Hole-Accretion Disk System with Magnetic Connection: Limit of Low Accretion Rate

Cited by in corpus (6)

• Properties of Trans-fast Magnetosonic Jets in Black Hole Magnetospheres
• Implications from the velocity profile of the M87 jet: a possibility of a slowly rotating black hole magnetosphere
• Signatures of Black Hole Spin and Plasma Acceleration in Jet Polarimetry
• Matter density distribution of general relativistic highly magnetized jets driven by black holes
• Black Hole Aurora powered by a Rotating Black Hole
• Relativistic jet acceleration region in a black hole magnetosphere