General relativistic magnetized Bondi-Hoyle-Lyttleton accretion with a spin-field misalignment: Jet nutation, polarity reversals, and Magnus drag

TL;DR

This study uses 3D general relativistic magnetohydrodynamics simulations to explore how inclined magnetic fields and wind speeds affect accretion, jet formation, and black hole dynamics, revealing phenomena like jet nutation, polarity reversals, and Magnus-like drag.

Contribution

It presents the first detailed simulation of magnetized Bondi-Hoyle-Lyttleton accretion onto spinning black holes with magnetic field misalignment, uncovering new jet and disk behaviors.

Findings

Magnetically arrested accretion leads to intermittent jet formation.

Jet bending and confinement depend on upstream ram pressure.

Magnetic polarity reversals occur when the magnetic field is perpendicular to the black hole spin.

Abstract

The dynamics of a black hole traveling through a plasma--a general relativistic extension of the classic Bondi-Hoyle-Lyttleton (BHL) accretion problem--can be related to a variety of astrophysical contexts, including the aftermath of binary black hole mergers in gaseous environments. We perform three-dimensional general relativistic magnetohydrodynamics simulations of BHL accretion onto a spinning black hole when magnetic field of the incoming wind is inclined to the spin axis of the black hole. Irrespective of inclination but dependent on the wind speed, we find that the accretion flow onto the black hole can become magnetically arrested, launching an intermittent jet whose formation is assisted by a turbulent dynamo-like process in the inner disk. The upstream ram pressure of the wind bends the jet, and confines the angular extent into which the magnetic flux tubes ejected from quasiperiodic eruptions are released. Recoil from magnetic flux eruptions drives strong oscillations in the inner accretion disk, resulting in jet nutation at the outer radii and occasionally ripping off the inner part of the accretion disk. When the incoming magnetic field is perpendicular to the spin axis of the black hole, we find that the magnetic polarity of the jets can undergo a stochastic reversal. In addition to dynamical friction, the black hole experiences a perpendicular drag force analogous to the Magnus effect. Qualitative effects of the incoming magnetic field orientation, the strength of the magnetization, and the incoming wind speed are investigated as well.