Figure 10 - uploaded by Biplob Sarkar
Content may be subject to copyright.
Typical spectra from an accretion disc around a black hole of mass M = 10M ⊙ for a strong and weak accretion shock located at xs = 13.14 and 72.12 respectively. The two different shock locations correspond to flows injected from the outer edge with two different values of β as indicated in the figure. See text for details.
Source publication
We investigate the global structure of the advection dominated accretion flow around a Schwarzschild black hole where the accretion disc is threaded by toroidal magnetic fields. We consider synchrotron radiative process as an effective cooling mechanism active in the flow. With this, we obtain the global transonic accretion solutions by exploring t...
Similar publications
Based on the theory of magnetoacoustic coupled dynamics, the purpose of this paper is to evaluate the dynamic stress concentration near an elliptical opening in exponential-gradient piezomagnetic materials under the action of antiplane shear waves. By the wave function expansion, the solutions for the acoustic wave fields and magnetic fields can be...
A bstract
We consider a neutral holographic plasma with dynamical electromagnetic interactions in a finite external magnetic field. The Coulomb interactions are introduced via mixed boundary conditions for the Maxwell gauge field. The collective modes at finite wave-vector are analyzed in detail and compared to the magneto-hydrodynamics results val...
The quality of today's research is often tightly limited to the available computing power and scalability of codes to many processors. For example, tackling the problem of heating the solar corona requires a most realistic description of the plasma dynamics and the magnetic field. Numerically solving such a magneto-hydrodynamical (MHD) description...
In this work, the buoyancy-driven unsteady flow of Casson nanofluid is analyzed. The effects of Brownian motion and thermophoresis on the flow fields are studied in the presence of magnetic field. Moreover, the convective boundary conditions on temperature and concentration walls are also considered. The similarity solutions are obtained numericall...
We present simulations of magnetic reconnection with a newly developed coupled MHD-PIC code. In this work a global magnetohydrodynamic (MHD) simulation receives kinetic feedback within an embedded region that is modeled by a kinetic particle-in-cell (PIC) code. The PIC code receives initial and boundary conditions from the MHD simulation, while the...
Citations
... It is shown that in the region r > 8 r g , the ratio of the radial velocity of the fluid element to the speed of light is of the order 10 −1 , cf. [75] and references therein. So, we have V 2 c 2 ∼ 10 −2 . ...
... Further, we find two real roots for the 'X'-type critical points: dV dr | rc < 0, which corresponds to accretion, and the other dV dr | rc > 0 refers to the wind solutions (see [11,73] and references therein). It is also important to note that the flow possessing MCPs can potentially harbor shock waves [10,14,75], such scenarios are beyond the scope of this paper. ...
We present the structure of a low angular momentum accretion flows around rotating compact objects incorporating relativistic corrections up to the leading post-Newtonian order. To begin with, we formulate the governing post-Newtonian hydrodynamic equations for the mass and energy-momentum flux without imposing any symmetries. However, for the sake of simplicity, we consider the flow to be stationary, axisymmetric, and inviscid. Toward this, we adapt the polytropic equation of state (EoS) and analyze the vertically integrated accretion flow confined to the equatorial plane. It is shown that the spin-orbit effects manifest themselves in the accretion dynamics. In the present analysis, we focus on global transonic accretion solutions, where a subsonic flow enters far away from the compact object and gradually gains radial velocity as it moves inwards. Thus, the flow becomes supersonic after reaching a certain radius, known as the critical point. To better understand the transonic solutions and examine the effect of post-Newtonian corrections, we classify the post-Newtonian equations into semi-relativistic (SR), semi-Newtonian (SN), and non-relativistic (NR) limits and compare the accretion solutions and their corresponding flow variables. With these, we find that SR and SN flow are in good agreement all throughout, although they deviate largely from the NR ones. Interestingly, the density profile seems to follow the profile ρ ∝ r −3/2 in the post-Newtonian regime. The present study has the potential to connect Newtonian and GR descriptions of accretion dynamics.
... Hence, flow must change its sonic state to become transonic (Fukue 1987;Chakrabarti 1989;Takahashi et al. 2002) at a radius commonly known as critical point. Depending on the flow parameters, namely energy, angular momentum and magnetic fields, flow may contain either single or multiple critical points (Sarkar & Das 2016;Sarkar et al. 2018;Mitra et al. 2022). Note that multi-transonic flows often exhibit discontinuous shock transitions (Fukue 1987;Chakrabarti 1989;Das et al. 2001a;Takahashi et al. 2002). ...
... Because of this, matter accumulates in the vicinity of the BH, and a barrier is formed in the form of an effective boundary layer around BH. Such a centrifugal barrier cannot hold the accumulation of matter indefinitely and beyond a critical limit, it eventually triggers the discontinuous transition of the flow variables in the form of shock waves (Fukue 1987;Chakrabarti 1989;Frank et al. 2002;Takahashi et al. 2002;Das & Chakrabarti 2007;Sarkar & Das 2016;Sarkar et al. 2018;Dihingia et al. 2019Dihingia et al. , 2020. Considering this, we describe the shock conditions for MHD flow in the GR framework below, which eventually enables us to study shock properties, namely shock location (r sh ), shock compression ratio (R), and shock strength (Ψ). ...
We investigate the global structure of general relativistic magneto-hydrodynamic (GRMHD) accretion flows around Kerr black holes containing shock waves, where the disk is threaded by radial and toroidal magnetic fields. We self-consistently solve the GRMHD equations that govern the flow motion inside the disk and for the first time to our knowledge, we obtain the shock-induced global GRMHD accretion solutions around weakly as well as rapidly rotating black holes for a set of fundamental flow parameters, such as energy ($E$), angular momentum ($L$), radial magnetic flux ($\Phi$), and iso-rotation parameter ($F$). We show that shock properties, namely shock radius ($r_{\rm sh}$), compression ratio ($R$) and shock strength ($\Psi$) strongly depends on $E$, $L$, $\Phi$, and $F$. We observe that shock in GRMHD flow continues to exist for wide range of the flow parameters, which allows us to identify the effective domain of parameter space in $L-E$ plane where shock solutions are feasible. Moreover, we examine the modification of the shock parameter space and find that it shifts towards the lower angular momentum values with increasing $\Phi$ and black hole spin ($a_{\rm k}$). Finally, we compute the critical radial magnetic flux ($\Phi^{\rm cri}$) that admits shocks in GRMHD flow and ascertain that $\Phi^{\rm cri}$ is higher (lower) for black hole of spin $a_{\rm k} = 0.99$ ($0.0$) and vice versa.
... However, the effect of thermal conduction on the accretion solutions is prominently visible in the region far from the black hole horizon. We keep increasing the saturation constant to a critical value Φs = 0.000425 (dot-dashed curve in green), beyond that the flow fails to connect the outer edge as the solution becomes closed (Sarkar et al. 2018), shown using a dotted (magenta) curve. If we keep increasing Φs, we continue to ob- tain closed solutions depicted in long-dashed (blue) and dotdashed (purple) curves. ...
We examine the effect of thermal conduction on the low-angular momentum hot accretion flow (HAF) around non-rotating black holes accreting mass at very low rate. While doing so, we adopt the conductive heat flux in the saturated form, and solve the set of dynamical equations corresponding to a steady, axisymmetric, viscous, advective accretion flow using numerical methods. We study the dynamical and thermodynamical properties of accreting matter in terms of the input parameters, namely energy ($\varepsilon_0$), angular momentum ($\ell_0$), viscosity parameter ($\alpha$), and saturation constant ($\Phi_{\rm s}$) regulating the effect of thermal conduction. We find that $\Phi_{\rm s}$ plays a pivotal role in deciding the transonic properties of the global accretion solutions. In general, when $\Phi_{\rm s}$ is increased, the critical point ($r_{\rm c}$) is receded away from the black hole, and flow variables are altered particularly in the outer part of the disc. To quantify the physically acceptable range of $\Phi_{\rm s}$, we compare the global transonic solutions with the self-similar solutions, and observe that the maximum saturation constant ($\Phi^{\rm max}_{\rm s}$) estimated from the global solutions exceeds the saturated thermal conduction limit ($\Phi_{\rm sc}$) derived from the self-similar formalism. Moreover, we calculate the correlation between $\alpha$ and $\Phi^{\rm max}_{\rm s}$ and find ample disagreement between global solutions and self-similar solutions. Further, using the global flow variables, we compute the Bernoulli parameter ($Be$) which remains positive all throughout the disc, although flow becomes loosely unbound for higher $\Phi_{\rm s}$. Finally, we indicate the relevance of this work in the astrophysical context in explaining the possibility of massloss/outflows from the unbound disc.
... The first bounds on shock wave stability lead to a simple condition: inner shocks are unstable, and outer shocks are stable [36]. Following papers considered more general accretion disk models [37,38,39,50,15,51,18], nonaxisymmetric perturbations [20,21,35,28], and additional thermodynamic and electromagnetic effects [24,47,48]. ...
Most black holes possess accretion disks. Models of such disks inform observations and constrain the properties of the black holes and their surrounding medium. Here, we study shocks in a thin isothermal black hole accretion flow. Modelling infinitesimal viscosity allows the use of multiple-scales matched asymptotic methods. We thus derive the first explicit calculations of isothermal shock stability. We find that the inner shock is always unstable, and the outer shock is always stable. The growth/decay rates of perturbations depend only on an effective potential and the incoming–outgoing flow difference at the shock location. We give a prescription of accretion regimes in terms of angular momentum and black hole radius. Accounting for viscous angular momentum dissipation implies unstable outer shocks in much of parameter space, even for realistic viscous Reynolds numbers of the order ≈1020.
... The first bounds on shock wave stability lead to a simple condition: inner shocks are unstable, and outer shocks are stable [36]. Following papers considered more general accretion disk models [37,38,39,50,15,51,18], nonaxisymmetric perturbations [20,21,35,28], and additional thermodynamic and electromagnetic effects [24,47,48]. ...
Most black holes possess accretion disks. Models of such disks inform observations and constrain the properties of the black holes and their surrounding medium. Here, we study isothermal shocks in a thin black hole accretion flow. Modelling infinitesimal molecular viscosity allows the use of multiple-scales matched asymptotic methods. We thus derive the first explicit calculations of isothermal shock stability. We find that the inner shock is always unstable, and the outer shock is always stable. The growth/decay rates of perturbations depend only on an effective potential and the incoming--outgoing flow difference at the shock location. We give a prescription of accretion regimes in terms of angular momentum and black hole radius. Accounting for angular momentum dissipation implies unstable outer shocks in much of parameter space, even for realistic viscous Reynolds numbers of the order $\approx 10^{20}$.
... As a useful supplement to the prevailing theory, the shocks in accretion flow, including axisymmetric, radially standing shocks and non-axisymmetric spiral shocks, have been rigorously investigated in the literature over the past few decades. A series of theoretical works proposed and gradually improved the radially standing shock model (Fukue 1987;Chakrabarti 1989;Lu et al. 1999;Becker & Kazanas 2001;Chakrabarti & Das 2004;Fukumura & Tsuruta 2004;Sarkar & Das 2016;Dihingia et al. 2018Dihingia et al. , 2019aDihingia et al. , 2019aSarkar et al. 2018). This model has been used to explain the observational spectral states and quasi-periodic oscillations of compact objects (Chakrabarti & Titarchuk 1995;Molteni et al. 1996). ...
We examine the properties of spiral shocks from a steady, adiabatic, non-axisymmetric accretion disk around a compact star in a binary. We first incorporate all possible influences from a binary through adopting the Roche potential and Coriolis forces in the basic conservation equations. In this paper, we assume spiral shocks to be point-wise and self-similar, and that the flow is in vertical hydrostatic equilibrium to simplify the study. We also investigate mass outflow due to shock compression and apply it to an accreting white dwarf in a binary. We find that our model will be beneficial for overcoming the ad hoc assumption of an optically thick wind generally used in studies of the progenitors of supernovae Ia.
... lixue@xmu.edu.cn (Fukue 1987;Chakrabarti 1989;Lu et al. 1999;Becker & Kazanas 2001;Fukumura & Tsuruta 2004;Chakrabarti & Das 2004;Sarkar & Das 2016;Sarkar et al. 2018;Dihingia et al. 2018Dihingia et al. , 2019b. This model has been used to explain the observational spectral states and quasiperiodic oscillations of compact objects (Chakrabarti & Titarchuk 1995;Molteni et al. 1996). ...
We examine the properties of spiral shocks from a steady, adiabatic, non-axisymmetric accretion disk around a compact star in binary. We first time incorporate all the possible influences from binary through adopting the Roche potential and Coriolis forces in the basic conservation equations. In this paper, we assume the spiral shocks to be point-wise self-similar, and the flow is in vertical hydrostatic equilibrium to simplify the study. We also investigate the mass outflow due to the shock compression and apply it to the accreting white dwarf in binary. We find that our model will be beneficial to overcome the ad hoc assumption of optically thick wind generally used in the studies of the progenitor of supernovae Ia.
... The value of α falls in the range α=0.23±0.1 estimated by Coroniti (1981) in a magnetic flux cell model (quoted in Sakimoto & Coroniti 1981), and agrees with α∼0.27 from steady-state models by Sarkar et al. (2018). Even though in different scales, for dwarf nova and X-ray transient outbursts one also finds α=0.25±0.15 ...
In the binary black hole model of OJ 287, the secondary black hole orbits a much more massive primary, and impacts on the primary accretion disk at predictable times. We update the parameters of the disk, the viscosity, α, and the mass accretion rate, m. We find α = 0.26±0.1 and m=0.08±0.04 in Eddington units. The former value is consistent with Coroniti, and the latter with Marscher & Jorstad. Predictions are made for the 2019 July 30 superflare in OJ 287. We expect that it will take place simultaneously at the Spitzer infrared channels, as well as in the optical, and that therefore the timing of the flare in optical can be accurately determined from Spitzer observations. We also discuss in detail the light curve of the 2015 flare, and find that the radiating volume has regions where bremsstrahlung dominates, as well as regions that radiate primarily in synchrotron radiation. The former region produces the unpolarized first flare, while the latter region gives rise to a highly polarized second flare.
Context. We investigate the properties of spiral shocks in a steady, adiabatic, non-axisymmetric, self-gravitating, mass-outflowing accretion disk around a compact object.
Aims. We obtained the accretion-ejection solutions in a galactic disk and applied them to spiral galaxies in order to investigate the possible physical connections between some observational quantities of galaxies.
Methods. We considered the self-gravitating disk potential to examine the properties of the galactic gaseous disk. We obtained spiral shock-induced accretion-ejection solutions following the point-wise self-similar approach.
Results. We observed that the self-gravitating disk profoundly affects the dynamics of the spiral structure of the disk and the properties of the spiral shocks. We find that the observational dispersion between the pitch angle and shear rate and between the pitch angle and star formation rate in spiral galaxies contains some important physical information.
Conclusions. There are large differences among the star formation rates of galaxies with similar pitch angles. These differences may be explained by the different star formation efficiencies caused by distinct galactic ambient conditions.
We examine the effect of thermal conduction on the low-angular momentum hot accretion flow (HAF) around non-rotating black holes accreting mass at very low rate. While doing so, we adopt the conductive heat flux in the saturated form, and solve the set of dynamical equations corresponding to a steady, axisymmetric, viscous, advective accretion flow using numerical methods. We study the dynamical and thermodynamical properties of accreting matter in terms of the input parameters, namely energy (ϵ0), angular momentum (ℓ0), viscosity parameter (α), and saturation constant (Φs) regulating the effect of thermal conduction. We find that Φs plays a pivotal role in deciding the transonic properties of the global accretion solutions. In general, when Φs is increased, the critical point (rc) is receded away from the black hole, and flow variables are altered particularly in the outer part of the disc. To quantify the physically acceptable range of Φs, we compare the global transonic solutions with the self-similar solutions, and observe that the maximum saturation constant (|$\Phi ^{\rm max}_{\rm s}$|) estimated from the global solutions exceeds the saturated thermal conduction limit (Φsc) derived from the self-similar formalism. Moreover, we calculate the correlation between α and |$\Phi ^{\rm max}_{\rm s}$| and find ample disagreement between global solutions and self-similar solutions. Further, using the global flow variables, we compute the Bernoulli parameter (Be) which remains positive all throughout the disc, although flow becomes loosely unbound for higher Φs. Finally, we indicate the relevance of this work in the astrophysical context in explaining the possibility of massloss/outflows from the unbound disc.
