## About

75

Publications

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487

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Introduction

Additional affiliations

September 2012 - January 2016

September 2008 - present

September 2005 - September 2012

## Publications

Publications (75)

We investigate the dynamics of clumps that coexisted with/in advection-dominated accretion flows by considering thermal conductivity. Thermal conduction can be one of the effective factors in the energy transportation of ADAFs; hence it may indirectly affect the dynamics of clumps by means of a contact force between them and their host medium. We f...

We investigate the dynamics of clumps that coexisted with/in advection-dominated accretion flows by considering thermal conductivity. Thermal conduction can be one of the effective factors in the energy transportation of ADAFs; hence it may indirectly affect the dynamics of clumps by means of a contact force between them and their host medium. We f...

We study the global solutions of slowly rotating accretion flows around the supermassive black hole in the nucleus of an elliptical galaxy. The velocity of accreted gas surrounding the black hole is initially subsonic and then falls on to the black hole supersonically, so accretion flow must be transonic. We numerically solve equations from the Bon...

We study the global solutions of slowly rotating accretion flows around the supermassive black hole in the nucleus of an elliptical galaxy. The velocity of accreted gas surrounding the black hole is initially subsonic and then falls onto the black hole supersonically, so accretion flow must be transonic. We numerically solve equations from the Bond...

The present work proposes a new formalism for the inner regions of a neutrino-dominated accretion flows (NDAFs) by considering the self-gravity, where the neutrino opacity is high enough to make neutrinos trapped becoming a dominant factor in the transportation of energy and angular momentum over the magneto rotational instability. We investigate t...

The present work proposes a new formalism for the inner regions of a neutrino-dominated accretion flows (NDAFs) by considering the self-gravity, where the neutrino opacity is high enough to make neutrinos trapped becoming a dominant factor in the transportation of energy and angular momentum over the magneto rotational instability. We investigate t...

Filamentary molecular clouds are omnipresent in the cold interstellar medium. Observational evidences show that the non-isothermal equations of state describe the filaments properties better than the isothermal one. In this paper we use the logatropic and the polytropic equations of state to study the gravitational instability of the pressure-confi...

Filamentary molecular clouds are omnipresent in the cold interstellar medium. Observational evidences show that the non-isothermal equations of state describe the filaments properties better than the isothermal one. In this paper we use the logatropic and the polytropic equations of state to study the gravitational instability of the pressure-confi...

The main purpose of this paper is to obtain analytical solutions for radiative transfer equations related to the vertical structure of accretion discs with finite optical depth. In the non-grey atmosphere, we employ the optical-depth dependent Eddington factor to define the relationship between the mean intensity and radiation stress tensor. Analyt...

The main purpose of this paper is to obtain analytical solutions for radiative transfer equations related to the vertical structure of accretion discs with finite optical depth. In the non-gray atmosphere, we employ the optical-depth dependent Eddington factor to define the relationship between the mean intensity and radiation stress tensor. Analyt...

The evolution of disk galaxies in modified gravity is studied by using high-resolution N-body simulations. More specifically, we use the weak field limit of two modified gravity theories, i.e., nonlocal gravity (NLG) and scalar-tensor-vector gravity known as MOG, and ignore the existence of dark matter halo. On the other hand, we construct the same...

The evolution of disk galaxies in modified gravity is studied by using high-resolution N-body simulations. More specifically, we use the weak field limit of two modified gravity theories, i.e., nonlocal gravity (NLG) and scalar-tensor-vector gravity known as MOG, and ignore the existence of dark matter halo. On the other hand, we construct the same...

X-ray flares can be accounted for a hint to the late time activity of Gamma-ray bursts (GRBs) central engines. Such a long term activity has been described through some models, one of which is the viscous evolution of the outer disc fragments that proposed by Perna et al. (2006), and developed quantitatively by Dall Osso et al. (2017). Here, we rec...

We study the local thermal stability of thin accretion disks. We present a full stability analysis in the presence of a magnetic field and more importantly wind. For wind, we use a general model suitable for adequately describing several kinds of winds. First, we explicitly show that the magnetic field, irrespective of the type of wind, has a stabi...

The classical Bondi model is adopted to study accretion onto the finite luminous region around the central massive black hole (MBH) in an elliptical galaxy. Unlike Bondi (1952), we define the boundary conditions at a certain finite radius (rf) instead of at the infinity and examine the variation of solutions for a simple case. In the following, we...

The classical Bondi model is adopted to study accretion onto the finite luminous region around the central massive black hole (MBH) in an elliptical galaxy. Unlike Bondi (1952), we define the boundary conditions at a certain finite radius ($r_f$) instead of at the infinity and examine the variation of solutions for a simple case. In the following,...

By taking into account photon absorption, we investigate the vertical structure of accretion flows with comparable radiation and gas pressures. We consider two separate energy equations for matter and radiation in the diffusion limit. In order to solve the set of radiation hydrodynamic equations in steady state and axisymmetric configuration, we em...

By taking into account photon absorption, we investigate the vertical structure of accretion flows with comparable radiation and gas pressures. We consider two separate energy equations for matter and radiation in the diffusion limit. In order to solve the set of radiation hydrodynamic equations in steady state and axisymmetric configuration, we em...

We implement a new semi-analytical approach to investigate radially self-similar solutions for the steady-state advection-dominated accretion flows (ADAFs). We employ the usual α-prescription for the viscosity, and all components of the energy-momentum tensor are considered. In this case, in the spherical coordinate, the problem reduces to a set of...

The relativistic version of the gravitational instability criterion is studied in the first order of the post-Newtonian limit. In other words, we investigate the post-Newtonian Jeans analysis for a self-gravitating system whose characteristic velocity and corresponding gravitational field limit to the post-Newtonian regime. We find the first relati...

The relativistic generalization of the Jeans analysis is studied in the first post-Newtonian approximation. In fact, we investigate the local gravitational instability for a self-gravitating fluid in which characteristic velocity of the system and corresponding gravitational field can be relativistic and valid beyond Newtonian limit. To do so, the...

We implement a new semi-analytical approach to investigate radially self-similar solutions for the steady-state advection-dominated accretion flows (ADAFs). We employ the usual $\alpha$-prescription for the viscosity and all the components of the energy-momentum tensor are considered. In this case, in the spherical coordinate, the problem reduces t...

The existence of outflow in the advection dominated accretion flows has been confirmed by both numerical simulations and observations. The outow models for ADAF have been investigated by several groups with a simple self similar solution. But this solution is inaccurate at the inner regions and can not explain the emitted spectrum of the flow; so,...

We solved one-dimensional hydrodynamic (HD) equations of the slim disks in the presence of the wind and in cylindrical. coordinates using self-similar solution. We considered power-law function of for mass loss rate due to wind. Then, we considered mass loss, angular-momentum loss and energy loss in equations. Then, we treated the influence of wind...

Recent observations of the filamentary molecular clouds show that their properties deviate from the isothermal equation of state. Theoretical investigations proposed that the logatropic and the polytropic equations of state with negative indexes can provide a better description for these filamentary structures. Here, we aim to compare the effects o...

We solved the set of two-dimensional magnetohydrodynamic (MHD) equations for optically thin black hole accretion flows incorporating toroidal component of magnetic field. Following global and local MHD simulations of black hole accretion disks, the magnetic field inside the disk is decomposed into a large scale field and a fluctuating field. The ef...

We investigate the properties of a hot accretion flow bathed in a poloidal magnetic field. We consider an axisymmetric viscous resistive flow in the steady state configuration. We assume the dominant mechanism of energy dissipation is due to turbulence viscosity and magnetic diffusivity. A certain fraction of that energy can be advected towards the...

What is conducted in the present work is the study of self-gravity effects on vertical structure of magnetized neutrino-dominated accretion disc (termed NDAF and considered as a central engine for Gamma-ray bursts (GRBs)). Some of the disc physical time scales such as viscous, cooling and diffusion time scales, that are supposed to play a pivotal r...

The recent observations of rippled structures on the surface of the Orion molecular cloud (Bern\'{e} et al. 2010), have been attributed to the Kelvin-Helmholtz (KH) instability. The wavelike structures which have mainly seen near star-forming regions taking place at the interface between the hot diffuse gas, which is ionized by massive stars, and t...

We present the effects of ordered large scale magnetic field on the structure of supercritical accretion flow in the presence of outflow. In the cylindrical coordinates ($r, \varphi,z$), We write the 1.5 dimensional, the steady state ($\frac{\partial}{\partial t}=0$) and axisymmetric ($\frac{\partial}{\partial \varphi}=0$) inflow-outflow equations...

This paper explores the effects of large-scale magnetic fields in hot accretion flows for asymmetric configurations with respect to the equatorial plane. The solutions that we have found show that the large-scale asymmetric magnetic field can significantly affect the dynamics of the flow and also cause notable outflows in the outer parts. Previousl...

The Jeans analysis is studied in the first post-Newtonian limit. In other words, the relativistic effects on the local gravitational instability are considered for systems where characteristic velocity of the system and corresponding gravitational field are higher than what permitted in Newtonian limit. The dispersion relation for propagation of sm...

We examine the effects of a global magnetic field and outflow on radiatively inefficient accretion flow (RIAF) in the presence of magnetic resistivity. We find self-similar solutions for the height integrated equations that govern the behavior of the flow. We use the mixing length mechanism for studying the convection parameter. We adopt the radius...

The gravitational instability of a filamentary molecular cloud in non-ideal magnetohydrodynamics is investigated. The filament is assumed to be in hydrostatic equilibrium. We add the effect of ambipolar diffusion to the filament which is threaded by an initial uniform axial magnetic field along its axis. We write down the fluid equations in cylindr...

We obtain two-dimensional exact analytic solutions for the structure of the hot accretion flows without wind. We assume that the only non-zero component of the stress tensor is $T_{r\varphi}$. Furthermore we assume that the value of viscosity coefficient $\alpha$ varies with $\theta$. We find radially self-similar solutions and compare them with th...

We study the global gravitational stability of a gaseous self-gravitating Maclaurin disk in the absence of a halo. Further, we replace Newtonian gravity with the specific Modified gravity theory known as MOG in the relevant literature. MOG is an alternative theory for addressing the dark matter problem without invoking exotic dark matter particles,...

We solve the radiation-hydrodynamic (RHD) equations of supercritical accretion flows in the presence of radiation force and outflow by using self similar solutions. Compare with the pioneer works, in this paper we consider power-law function for mass inflow rate as $ \dot{M} \propto r^{s} $. We found that $ s = 1 $ when the radiative cooling term i...

We study Active Galactic Nucleus (AGN) activity in the fossil galaxy cluster,
RX J1416.4+2315. Radio observations were carried out using Giant Metrewave
Radio Telescope (GMRT) at two frequencies, 1420 MHz and 610 MHz. A weak radio
lobe that extends from the central nucleus is detected in 610 MHz map. Assuming
the radio lobe originated from the cent...

We present the effect of a hydrodynamical wind on the structure and the
surface temperature of a vertically self-gravitating magnetized ADAFs using
self-similar solutions. Also a model for an axisymmetric, steady-state,
vertically self-gravitating hot accretion flow threaded by a toroidal magnetic
field has been formulated. The model is based on $\...

We construct self-similar inflow–outflow solutions for a hot viscous–resistive accretion flow with large-scale magnetic fields
that have odd symmetry with respect to the equatorial plane in Bθ and even symmetry in Br and Bϕ. Following previous authors, we also assume that the polar velocity vθ is non-zero. We focus on four parameters: βr0, βϕ0 (the...

We solve the set of hydrodynamic (HD) equations for optically thin Advection
Dominated Accretion Flows (ADAFs) by assuming radially self-similar in
spherical coordinate system $ (r, \theta, \phi) $. The disk is considered to be
steady state and axi-symmetric. We define the boundary conditions at the pole
and the equator of the disk and to avoid sin...

In the framework of metric $f(R)$ gravity, we find the dispersion relation
for the propagation of tightly wound spiral density waves in the surface of
rotating, self-gravitating disks. Also, new Toomre-like stability criteria for
differentially rotating disks has been derived for both fluid and stellar
disks.

We find the dispersion relation for tightly wound spiral density waves in the
surface of rotating, self-gravitating disks in the framework of Modified
Gravity (MOG). Also, the Toomre-like stability criterion for differentially
rotating disks has been derived for both fluid and stellar disks. More
specifically, the stability criterion can be express...

MOdified Gravity (MOG) is a covariant modification of Einstein's general
relativity. This theory is one of the current alternatives to dark matter
models. We describe dynamics of collisionless self-gravitating systems in the
context of MOG. By studying the weak field approximation of this theory, we
derive the equations governing the dynamics of th...

Dynamics of clumps within a magnetized advection dominated accretion flow is
investigated by solving the collisionless Boltzmann equation and considering
the drag force due to the relative velocity between the clumps and the gas.
Toroidal component of the magnetic field is assumed to be dominant. Dynamical
properties of the hot gaseous component su...

We investigate the Hall effect in a standard magnetized accretion disk which is accompanied by dissipation due to viscosity and magnetic resistivity. By considering an initial magnetic field, using the PLUTO code, we perform a numerical magnetohydrodynamic simulation in order to study the effect of Hall diffusion on the physical structure of the di...

By taking into account the effect of a toroidal magnetic field and its corresponding heating, we determine the thickness of
advection-dominated accretion flows. We consider an axisymmetric, rotating, steady viscous–resistive, magnetized accretion
flow under an advection-dominated stage. The dominant mechanisms of energy dissipation are assumed to b...

The main aim of this paper is studying the effect of toroidal magnetic field
on the structure of Advection-Dominated Accretion Flows (ADAF) in the presence
of the turbulence viscosity and diffusivity due to viscosity and magnetic field
respectively. We use self-similar assumption in radial direction to solve the
magnetohydrodynamic (MHD) equations...

We examine the effect of thermal conduction on the observational properties
of a super critical hot magnetized flow. We obtained self-similar solution of a
magnetized disc when the thermal conduction plays an important role. Follow of
our first paper (Ghasemnezhad et al. 2012 (hereafter GKA12)) we have extended
our solution on the observational app...

Given the fact that accretion discs are associated with their parent
molecular cloud, we studied its effects as a constraint on the outer boundary
of the viscous polytropic self-gravitating accretion flows subject to
the mass and angular momentum loss.

Self-similar and semi-analytical solutions are found for the height-averaged
equations govern the dynamical behavior of a polytropic, self-gravitating disk
under the effects of winds, around the nascent object. In order to describe
time evolution of the system, we adopt a radius dependent mass loss rate, then
highlight its importance on both the tr...

We have explored the structure of hot flow bathed in a general large-scale
magnetic field. The importance of outflow and thermal conduction on the
self-similar structure of a hot accretion flows has been investigated. We
consider the additional magnetic parameters $ \beta_{r,\varphi,z}\big[=
c^2_{r,\varphi,z}/(2 c^2_{s}) \big] $, where $ c^2_{r,\va...

The existence of outflow and magnetic field in the inner region of hot
accretion flows have been confirmed by observations and numerical
magnetohydrodynamic simulations (MHD). We present self-similar solutions for
radiation inefficiently accretion flows (RIAF) around black holes in the
presence of outflow and global magnetic field. The influence of...

We have studied the structure of hot accretion flow bathed in a general large-scale magnetic field. We have considered magnetic parameters \(\beta_{r,\varphi,z}[=c^{2}_{r,\varphi,z}/(2c^{2}_{s})] \), where \(c^{2}_{r, \varphi, z} \) are the Alfvén sound speeds in three direction of cylindrical coordinate (r,φ,z). The dominant mechanism of energy di...

We have explored the structure of hot magnetized accretion flow with thermal
conduction. The importance of thermal conduction in hot accretion flows has
been confirmed by observations of the hot gas surrounding Sgr $A^*$ and a few
other nearby galactic nuclei. For a steady state structure of such accretion
flows a set of self similar solutions are...

Force due to the self-gravity of the disc in the vertical direction is
considered to study its possible effects on the structure of a magnetized
advection-dominated accretion disc. We present steady-sate self similar
solutions for the dynamical structure of such a type of the accretion flows.
Our solutions imply reduced thickness of the disc becaus...

The combined impact of rotation and magnetic fields on oscillations of stellar fluids is still not well known theoretically. It mixes Alfvén and inertial waves. Neutron stars are a place where both effects may be at work. We aim to solve this problem in the context of the r-mode instability in neutron stars, as it appears when these modes are coupl...

In this paper, the effect of troidal magnetic field is studied in standard self-gravitating thin disks with β priscription. By applying the magnetic field, we expect to see different behaviors compared to a non-magnetic field case. The study reveals self-similar solutions for radial in fall velocity, rotation velocity, surface density and mass accr...

The ability to predict the future behavior of solar activity has become of
extreme importance due to its effect on the near Earth environment. Predictions
of both the amplitude and timing of the next solar cycle will assist in
estimating the various consequences of Space Weather. The level of solar
activity is usually expressed by international sun...

Observations of the hot gas, which is surrounding Sgr A* and a few other nearby galactic nuclei, imply that mean free paths of electron and proton are comparable to gas capture radius. So, hot accretion flows likely proceed under week collision conditions. As a result thermal conduction by ions has a considerable contribution in transfer of the rea...

We examine the effects of a hydrodynamical wind on advection dominated accretion flows with thermal conduction in the presence of a toroidal magnetic field under a self-similar treatment. The disk gas is assumed to be isothermal. For a steady state structure of such accretion flows a set of self similar solutions are presented. The mass-accretion r...

Observations of the hot gas that surrounds Sgr A* and a few other nearby galactic nuclei imply that the mean free paths of
electrons and protons are comparable to the gas capture radius. Hot accretion flows therefore likely proceed under weak collision
conditions. As a result, thermal conduction by ions has a considerable contribution to the transf...

Observations of the hot gas, which is surrounding Sgr A* and a few other nearby galactic nuclei, imply that mean free paths of electron and proton are comparable to gas capture radius. So, hot accretion flows likely proceed under week collision conditions. As a result thermal conduction by ions has a considerable contribution in transfer of the rea...

Duschl et al. (2000) have shown that the standard model for geometrically thin accretion disks ($\alpha$-disks) leads to inconsistency if self-gravity play a role. This problem arise from parametrization of viscosity in terms of local sound velocity and vertical disks scale hight. The $\beta$-viscosity prescription was introduced by Duschl et al. (...

The observation of the hot gas surrounding Sgr $A^*$ and a few other nearby
galactic nuclei imply that electron and proton mean free paths are comparable
to the gas capture radius. So, the hot accretion flows is likely to proceed
under week-collision conditions. Hence, thermal conduction has been suggested
as a possible mechanism by which the suffi...

We investigate the effect of self-gravity on the equilibrium structure of a thick non-rotating disk around a central object by the self-similar method. We introduce three dimensionless variables C sg , C t and C k that indicate the relative importance of self-gravity, thermal energy and kinetic energy, respectively. We study the effect of each of t...

We carry out self-similar solutions of viscous–resistive accretion flows around a magnetized compact object. We consider an
axisymmetric, rotating, isothermal steady accretion flow, which contains a poloidal magnetic field of the central star. The
dominant mechanism of energy dissipation is assumed to be the turbulence viscosity and magnetic diffus...

We carry out the self-similar solutions of viscous-resistive accretion flows around a magnetized compact object. We consider an axisymmetric, rotating, isotheral steady accretion flow which contains a poloidal magnetic field of the central star. The dominant

We carry out the effect of $\beta$-prescription for viscosity which
introduced by Duschel et al. 2000 & Hure, Richard & Zhan 2001, in a standard
self-gravitating thin disks. We were predicted in a self-gravitating thin disk
the $\beta$-model will have different dynamical behavior compare the well known
$\alpha$-prescriptions. We used self-similar m...

We examine the effect of self-gravity in a rotating thick-disc equilibrium in the presence of a dipolar magnetic field. First, we find a self-similar solution for non-self-gravitating discs. The solution that we have found shows that the pressure and density equilibrium profiles are strongly modified by a self-consistent toroidal magnetic field. We...

Both theoretical studies and observational features of Type-I X-ray bursts reveal that weakly-magnetic (B˜ 108-109 G) but high rate accreting (>10-9 M&sun; yr-1) neutron star in low mass X-ray binaries (LMXBs) burns the accreting hydrogen and helium to mid-weight elements like C O Ne etc. and accumulates a massive degenerate liquid ocean with densi...

## Projects

Project (1)

In this project we investigate effect of non-ideal MHD (currently ambipolar diffusion) on stability of filamentary molecular clouds with different equation of states.