Computation of mass loss from viscous accretion disc in presence of cooling (original) (raw)
Related papers
Estimation of the mass outflow rates from viscous accretion discs
Monthly Notices of the Royal Astronomical Society, 2013
We study the viscous accretion disc around black holes, and all possible accretion solutions, including shocked as well as shock-free accretion branches. Shock-driven bipolar outflows from a viscous accretion disc around a black hole have been investigated. One can identify two critical viscosity parameters, α cl and α cu , within which the stationary shocks may occur, for each set of boundary conditions. Adiabatic shock has been found for up to viscosity parameter α = 0.3, while in the presence of dissipation and mass loss we have found stationary shock up to α = 0.15. The mass outflow rate may increase or decrease with the change in disc parameters, and is usually around a few to 10 per cent of the mass inflow rate. We show that for the same outer boundary condition, the shock front decreases to a smaller distance with the increase in α. We also show that the increase in dissipation reduces the thermal driving in the post-shock disc, and hence the mass outflow rate decreases up to a few per cent.
Mass-loss from advective accretion disc around rotating black holes
Monthly Notices of the Royal Astronomical Society, 2015
We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter, PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (E) and specific angular momentum (λ) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole (a k) plays an important role in deciding the outflow rate Rṁ (ratio of mass flux of outflow and inflow), in particular, Rṁ is directly correlated with a k for the same set of inflow parameters. It is found that a large range of the inflow parameters allows global accretion-ejection solutions and the effective area of the parameter space (E, λ) with and without outflow decreases with black hole spin (a k). We compute the maximum outflow rate (R maẋ m) as function of black hole spin (a k) and observe that R maẋ m weakly depends on a k that lies in the range ∼ 10% − 18% of the inflow rate for the adiabatic index (γ) with 1.5 γ 4/3. We present the observational implication of our approach while studying the steady/persistent Jet activities based on the accretion states of black holes. We discuss that our formalism seems to have the potential to explain the observed Jet kinetic power for several Galactic Black Hole sources (GBHs) and Active Galactic Nuclei (AGNs).
Effect of the flow composition on outflow rates from accretion discs around black holes
We studied the outflow behaviour from accretion discs around black holes taking into account the vertical equilibrium accretion flow model. The outflow rate is found to depend crucially on flow composition. Our approach is to study the outflow behaviour as function of inflow around black holes with an equation of state which allows flow to be thermally relativistic close to black holes and non-relativistic far away from black holes. We studied shock ejection model. A pure electron–positron pair flow never undergoes shock transition while presence of some baryons (common in outflows and jets) makes it possible to have standing shock waves in the flow. It can be concluded that the presence of protons is necessary for the flow to show the outflow behaviour. The outflow rate is maximum when the flow contains the proton number density which is 27 per cent of the electron number density. We conclude that a pure electron–positron jet is unlikely to form.
Mass loss from a viscous accretion disc in presence of cooling
2006
We compute the mass loss from a viscous advective disc, which undergoes centrifugal pressure mediated shock. We show that for same outer boundary condition of the disc, the mass outflow rate decreases with increasing viscosity, since viscosity weakens the centrifugal barrier that generates the shock. We also show that in presence of cooling the mass outflow rate decreases marginally, which shows that these outflows are basically centrifugally driven. We also show that the optical depth of the disc for external photons entering the post shock disc is decreased because of mass loss, and hence should soften the spectrum.
Monthly Notices of the Royal Astronomical Society
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 the variety of boundary conditions and dissipation parameters, namely accretion rate (ṁ) and viscosity (α B). The fact that depending on the initial parameters, steady state accretion flows can possess centrifugally supported shock waves. These global shock solutions exist even when the level of dissipation is relatively high. We study the properties of shock waves and observe that the dynamics of the post-shock corona (hereafter, PSC) is regulated by the flow parameters. Interestingly, we find that shock solution disappears completely when the dissipation parameters exceed their critical values. We calculate the critical values of viscosity parameter (α cri B) adopting the canonical values of adiabatic indices as γ = 4/3 (ultrarelativistic) and 1.5 (seminon-relativistic) and find that in the gas pressure dominated domain, α cri B ∼ 0.4 for γ = 4/3 and α cri B ∼ 0.27 for γ = 1.5, respectively. We further show that global shock solutions are relatively more luminous compared to the shock free solutions. Also, we have calculated the synchrotron spectra for shocked solutions. When the shock is considered to be dissipative in nature, it would have an important implication as the available energy at PSC can be utilized to power the outflowing matter escaped from PSC. Towards this, we calculate the maximum shock luminosity and discuss the observational implication of our present formalism.
On the possibilities of mass loss from an advective accretion disc around stationary black holes
We study the coupled disc-jet system around the black hole where the outflow solutions are obtained in terms of the inflow parameters. We observe that an advective accretion disc can eject outflows/jets for wide range of viscosity parameter. However, such possibility is reduced if the cooling is active as the energy dissipative process inside the disc. For mass outflow, we obtain the parameter space spanned by the inflow angular momentum and the viscosity in terms of cooling and quantify the limits of viscosity parameter.
Monthly Notices of the Royal Astronomical Society, 2013
Using long-duration general relativistic magnetohydrodynamic simulations of radiatively inefficient accretion discs, the energy, momentum and mass outflow rates from such systems are estimated. Outflows occur via two fairly distinct modes: a relativistic jet and a subrelativistic wind. The jet power depends strongly on the black hole spin and on the magnetic flux at the horizon. Unless these are very small, the energy output in the jet dominates over that in the wind. For a rapidly spinning black hole accreting in the magnetically arrested limit, it is confirmed that jet power exceeds the total rate of accretion of rest mass energy. However, because of strong collimation, the jet probably does not have a significant feedback effect on its immediate surroundings. The power in the wind is more modest and shows a weaker dependence on black hole spin and magnetic flux. Nevertheless, because the wind subtends a large solid angle, it is expected to provide efficient feedback on a wide range of scales inside the host galaxy. Empirical formulae are obtained for the energy and momentum outflow rates in the jet and the wind.
The Astrophysical Journal, 2008
In this Letter, we present a new self-consistent theory for the production of the relativistic outflows observed from radio-loud black hole candidates and active galaxies as a result of particle acceleration in hot, viscous accretion disks containing standing, centrifugally-supported isothermal shocks. This is the first work to obtain the structure of such disks for a relatively large value of the Shakura-Sunyaev viscosity parameter (α = 0.1), and to consider the implications of the shock for the acceleration of relativistic particles in viscous disks. In our approach, the hydrodynamics and the particle acceleration are coupled and the solutions are obtained self-consistently based on a rigorous mathematical method. We find that particle acceleration in the vicinity of the shock can provide enough energy to power the observed relativistic jet in M87.
Periodic mass loss from viscous accretion flows around black holes
We investigate the behaviour of low angular momentum viscous accretion flows around black holes using smooth particle hydrodynamics method. Earlier, it has been observed that in a significant part of the energy and angular momentum parameter space, rotating transonic accretion flow undergoes shock transition before entering in to the black hole and a part of the post-shock matter is ejected as bipolar outflows, which are supposed to be the precursor of relativistic jets. In this work, we simulate accretion flows having injection parameters from the inviscid shock parameter space, and study the response of viscosity on them. With the increase of viscosity, shock becomes time dependent and starts to oscillate when the viscosity parameter crosses its critical value. As a result, the in falling matter inside the post-shock region exhibits quasi-periodic variations and causes periodic ejection of matter from the inner disc as outflows. In addition, the same hot and dense post-shock matter emits high energy radiation and the emanating photon flux also modulates quasi-periodically. Assuming a 10 M black hole, the corresponding power density spectrum peaks at the fundamental frequency of few Hz followed by multiple harmonics. This feature is very common in several outbursting black hole candidates. We discuss the implications of such periodic variations.
Mass Outflows from Dissipative Shocks in Hot Accretion Flows
The Astrophysical Journal, 2007
We consider stationary, axisymmetric hydrodynamic accretion flows in Kerr geometry. As a plausible means of efficiently separating a small population of nonthermal particles from the bulk accretion flows, we investigate the formation of standing dissipative shocks, i.e. shocks at which fraction of the energy, angular momentum and mass fluxes do not participate in the shock transition of the flow that accretes onto the compact object but are lost into collimated (jets) or uncollimated (winds) outflows. The mass loss fraction (at a shock front) is found to vary over a wide range (0% − 95%) depending on flow's angular momentum and energy. On the other hand, the associated energy loss fraction appears to be relatively low (1%) for a flow onto a non-rotating black hole case, whereas the fraction could be an order of magnitude higher (10%) for a flow onto a rapidly-rotating black hole. By estimating the escape velocity of the outflowing particles with a mass-accretion rate relevant for typical active galactic nuclei, we find that nearly 10% of the accreting mass could escape to form an outflow in a disk around a non-rotating black hole, while as much as 50% of the matter may contribute to outflows in a disk around a rapidly-rotating black hole. In the context of disk-jet paradigm, our model suggests that shock-driven outflows from accretion can occur in regions not too far from a central engine. Our results imply that a shock front under some conditions could serve as a plausible site where (nonthermal) seed particles of the outflows (jets/winds) are efficiently decoupled from bulk accretion.