Study of accretion processes around black holes becomes ‘Science’: Tell tale observational signatures of two component advective flows

Abstract

An accretion flow around a black hole has a saddle type sonic point just outside the event horizon to guarantee that the flow enters the black hole supersonically. This feature exclusively present in strong gravity limit makes its marks in every observation of black hole candidates. Another physical sonic point is present (as in a Bondi flow) even in weak gravity. Every aspect of spectral or temporal properties of every black hole can be understood using this transonic or advective flow having more than one saddle type points. This most well known and generalized solution with viscosity and radiative transfer has been verified by numerical simulations also. Spectra, computed for various combinations of the standard Keplerian, and advective sub-Keplerian components match accurately with those from satellite observations. Standing, oscillating and propagatory oscillating shocks are produced due to centrifugal barrier of the advective component. The post-shock region acts as the Compton cloud producing the power-law spectra. Jets and outflows are also produced from this post-shock region, commonly known as the CENtrifugal barrier supported BOundary Layer or CENBOL. In soft states, the CENBOL is cooled down by soft photons from the Keplerian disk, and thus the outflow is absent. Type-C and Type-B QPOs are generated respectively due to strong and weak resonance oscillations of the CENBOL. Away from resonance, oscillation may be triggered when Rankine-Hugoniot conditions are not satisfied and Type-A QPOs could be seen.

Properties of MAXI J1348-630 during Its Second Outburst in 2019

“…These models can explain the radiation spectra of black holes to some extent. In the mid 1990s, Chakrabarti and his collaborators came up with the Two Component Advective Flow (TCAF) solution based on transonic flow and radiative transport equations [26][27][28]. In this model, the accretion flow consists of two components: a geometrically thin, optically thick, high-viscosity Keplerian disk, and a low-viscosity, optically thin, sub-Keplerian flow or halo.…”

Accretion Flow Properties of MAXI J1910-057/Swift J1910.2-0546 During Its 2012-13 Outburst

“…Various models in literature attempt to explain the nature of this Compton cloud, e.g., magnetic corona (Galeev et al, 1979), disk-corona model (Haardt & Maraschi, 1993;Zdziarski et al, 1993), two-component advective flow (TCAF) solution (Chakrabarti & Titarchuk 1995, hereafter CT95;Chakrabarti 1997). According to the TCAF solution, the accretion disk consists of two components: an optically thick, geometrically thin, highly viscous Keplerian flow on the equatorial plane, and an optically thin, low viscous sub-Keplerian (low angular momentum) component encapsulating the Keplerian flow (for a review of TCAF, see Chakrabarti 2016). At a certain distance from the BH, the centrifugal pressure dominates over gravitational attraction, and the supersonic sub-Keplerian matter gets slowed down to become subsonic through a shock transition and gets piled-up behind the centrifugal barrier to form the CENtrifugal pressure supported BOundary Layer (CENBOL).…”