Neutral-charged-particle Collisions as the Mechanism for Accretion Disk Angular Momentum Transport

Abstract

The matter in an accretion disk must lose angular momentum when moving radially inwards but how this works has long been a mystery. By calculating the trajectories of individual colliding neutrals, ions, and electrons in a weakly ionized 2D plasma containing gravitational and magnetic fields, we numerically simulate accretion disk dynamics at the particle level. As predicted by Lagrangian mechanics, the fundamental conserved global quantity is the total canonical angular momentum, not the ordinary angular momentum. When the Kepler angular velocity and the magnetic field have opposite polarity, collisions between neutrals and charged particles cause: (i) ions to move radially inwards, (ii) electrons to move radially outwards, (iii) neutrals to lose ordinary angular momentum, and (iv) charged particles to gain canonical angular momentum. Neutrals thus spiral inward due to their decrease of ordinary angular momentum while the accumulation of ions at small radius and accumulation of electrons at large radius produces a radially outward electric field. In 3D, this radial electric field would drive an out-of-plane poloidal current that produces the magnetic forces that drive bidirectional astrophysical jets. Because this neutral angular momentum loss depends only on neutrals colliding with charged particles, it should be ubiquitous. Quantitative scaling of the model using plausible disk density, temperature, and magnetic field strength gives an accretion rate of 3 × 10−8 solar mass per year, which is in good agreement with observed accretion rates.

Signatures of regular black holes from the shadow of Sgr A* and M87*

“…with the electromagnetic field of the black hole [96,97]. This leads to a modification in the theoretical spectrum from the accretion disk and the epicyclic frequencies associated with the quasi-periodic oscillations [96,97]. Since photons are uncharged they do not directly interact with the electromagnetic field of the black hole.…”

Phase and Morphology of Water-ice Grains Formed in a Cryogenic Laboratory Plasma

“…Grains of water ice and dust are observed in many astrophysical environments, such as protoplanetary disks (Terada et al 2007) and interstellar clouds (Zubko et al 2004). These ice grains are formed from vapor at ultralow pressures and temperatures and typically exist within an environment that is weakly ionized by stellar radiation or cosmic rays (Ivlev et al 2015;Zhang & Bellan 2022). Grains acquire electric charge from this ambient plasma, as first noted by Spitzer (1941), because electrons have a higher collision frequency with the grains than do ions and so are collected by grains more frequently.…”