General Overview of Black Hole Accretion Theory

Abstract

I provide a broad overview of the basic theoretical paradigms of black hole accretion flows. Models that make contact with observations continue to be mostly based on the four decade old alpha stress prescription of Shakura & Sunyaev (1973), and I discuss the properties of both radiatively efficient and inefficient models, including their local properties, their expected stability to secular perturbations, and how they might be tied together in global flow geometries. The alpha stress is a prescription for turbulence, for which the only existing plausible candidate is that which develops from the magnetorotational instability (MRI). I therefore also review what is currently known about the local properties of such turbulence, and the physical issues that have been elucidated and that remain uncertain that are relevant for the various alpha-based black hole accretion flow models.

Continuum Reverberation Mapping of the Accretion Disks in Two Seyfert 1 Galaxies

“…It is also challenging to account for the X-ray-emitting corona from first principles , and there are a wide variety of hypothesized geometries and energetic connections between the corona and the accretion disk. Simulations have recently made progress by incorporating radiation transport (e.g., Saḑowski et al 2014;Saḑowski & Narayan 2015), but it has not been possible to simulate the full magneto-radiation-hydrodynamics of the disk that are fundamental for determining its observational appearance (Blaes 2014). It is also observationally difficult to isolate the intrinsic disk continuum due to line emission, host-galaxy starlight, and internal reddening, and the emission peak is generally unobservable due to absorption by intervening hydrogen.…”

Papaloizou–Pringle instability suppression by the magnetorotational instability in relativistic accretion discs

“…The discovery of the magnetorotational instability (MRI) in astrophysics by Balbus & Hawley (1991) provided a local mechanism, efficient for a wide range of magnetic field strength, which leads to a growth of linear perturbations on dynamical time-scales and naturally develops MHD turbulence. Since then, the properties of the MRI have been studied in great detail, from both a local and a global point of view (Balbus & Hawley 1998;Fromang 2013;Blaes 2014).…”

Non-linear mirror instability

“…This renders them unstable to fast (ion cyclotron timescale Ω −1 i ), small-scale (ion gyroscale ρ i ) firehose, mirror and ion cyclotron instabilities [1][2][3][4][5][6], whose observational signatures have been reported in the solar wind [7,8] and planetary magnetosheaths [9][10][11][12][13][14][15]. These instabilities are also thought to be excited in energetic astrophysical environments such as the intracluster medium (ICM) [16][17][18][19][20], the vicinity of accreting black holes [21][22][23], or the warm ionized interstellar medium [24,25], producing strong dynamical feedback at macroscales, with critical astrophysical implications [26][27][28][29][30][31]. A self-consistent description of the multiscale physics of such plasmas requires understanding how these instabilities saturate nonlinearly.…”