Jets from Time‐dependent Accretion Flows onto a Black Hole

Nobuta, Koji; Hanawa, Tomoyuki

doi:10.1086/306591

Cited by 27 publications

(40 citation statements)

References 20 publications

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“…They argued that the instability occurs owing to the energy input through the displacement of the shock wave, where the jump of the fluid density and displacement of the shock surface releasethe potential energy that amplifies the perturbations in the postshock flow. These results were later confirmed by Chakrabarti & Molteni (1993) and Nobuta & Hanawa (1994) through numerical simulations, assuming adiabatic flows with Rankine-Hugoniot standing shock waves and isothermal flows with isothermal standing shock waves, respectively.…”

Section: Introductionmentioning

confidence: 57%

“…Furthermore, shock stability analysis for thin disks has been studied using both analytical(e.g., Chakrabarti & Molteni 1993;Nakayama 1992Nakayama , 1994Nobuta & Hanawa 1994;Molteni et al 1996;Gu & Lu 2006;Nagakura & Yamada 2009) and numerical simulation approaches(e.g., Chakrabarti & Molteni 1993;Nobuta & Hanawa 1994;Molteni et al 1996;Gu & Lu 2006;Nagakura & Yamada 2008). However, several of these studies mainly focused on the assumption of a constant disk height(e.g., Chakrabarti & Molteni 1993;Nobuta & Hanawa 1994) or did not fully examine the multiple modes of oscillation(e.g., Chakrabarti & Molteni 1993;Nobuta & Hanawa 1994;Molteni et al 1996;Gu & Lu 2006;Nagakura & Yamada 2008), which are known to exist in the WD accretion shock case studied by, e.g., Chevalier & Imamura (1982) and Imamura et al (1984).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Furthermore, Nobuta & Hanawa (1994) showed that the fundamental and overtone modes with nonzero frequency are stable to both preshock acceleration and preshock deceleration, but the zerothmode with zero frequency is stable to preshock acceleration and unstable to preshock deceleration. In other words, Nobuta & Hanawa (1994) demonstrated that preshock deceleration and preshock acceleration are unstable and stable, respectively, using both linear and nonlinear treatments, consistent with the Nakayama instability. Gu & Foglizzo (2003) (assuming isothermal flows) and Gu & Lu (2006) (assuming adiabatic flows) later demonstrated that under a constant disk height assumption with isothermal standing shock waves the outer shock was generally non-axisymmetrically unstable when the shock Mach number was not close to unity, and argued that the advective-acoustic cycle between the corotation radius and the shock could be responsible for the instability.…”

Section: Introductionmentioning

confidence: 99%

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Standing Shock Instability in Advection-Dominated Accretion Flows

Wood

Wolff

et al. 2016

ApJ

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Depending on the values of the energy and angular momentum per unit mass in the gas supplied at large radii, inviscid advection-dominated accretion flows can display velocity profiles with either preshock deceleration or preshock acceleration. Nakayama has shown that these two types of flow configurations are expected to have different stability properties. By employing the Chevalier & Imamura linearization method and the Nakayama instability boundary conditions, we discover that there are regions of parameterspace where disks/shocks with outflows can be stable or unstable. In regions of instability, we find that preshock deceleration is always unstable to the zeroth mode with zero frequency of oscillation, but is always stable to the fundamental mode and overtones. Furthermore, we also find that preshock acceleration is always unstable to the zeroth modeand that the fundamental mode and overtones become increasingly less stable as the shock location moves away from the horizon when the disk half-height expands above ∼12 gravitational radii at the shock radius. In regions of stability, we demonstrate the zeroth mode to be stable for the velocity profiles that exhibit preshock acceleration and deceleration. Moreover, for models that are linearly unstable, our model suggests the possible existence of quasiperiodic oscillations (QPOs) with ratios 2:3 and 3:5. These ratios are believed to occur in stellar and supermassive black hole candidates, for example, in GRS 1915+105 and Sgr A * , respectively. We expect that similar QPO ratios also exist in regions of stable shocks.

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Section: Introductionmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Standing Shock Instability in Advection-Dominated Accretion Flows

Wood

Wolff

et al. 2016

ApJ

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“…In the literature, many authors from various groups published results of analytical viscous solutions as well as viscous hydro-dynamic simulations where it has been shown the shock is stable if the viscosity parameter is lower than a critical viscosity parameter (Chakrabarti 1990b(Chakrabarti , 1996dChakrabarti & Molteni 1995;Lanzafame, Molteni & Chakrabarti 1998;Lanzafame et al 2008;Lee, Ryu & Chattopadhyay 2011;Das et al 2014;Lee et al 2016). Also, there have been many stability studies of shock (Nakayama 1992(Nakayama , 1994Nobuta & Hanawa 1994;Gu & Foglizzo 2003;Gu & Lu 2006), but it was shown that even under non-axisymmetric perturbations, the shock tends to persist, albeit, as a deformed shock (Molteni, Tóth, & Kuznetsov 1999).…”

Section: Introductionmentioning

confidence: 99%

General relativistic numerical simulation of sub-Keplerian transonic accretion flows on to black holes: Schwarzschild space–time

Kim

Garain

Balsara

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We study time evolution of sub-Keplerian transonic accretion flows onto black holes using a general relativistic numerical simulation code. We perform simulations in Schwarzschild spacetime. We first compare one-dimensional simulation results with theoretical results and validate the performance of our code. Next, we present results of axisymmetric, two-dimensional simulation of advective flows. We find that even in this case, for which no complete theoretical analysis is present in the literature, steady state shock formation is possible.

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Jet Formation and Collimation

Sauty¹,

Tsinganos

Trussoni

Relativistic Flows in Astrophysics

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We briefly review our current understanding for the formation, acceleration and collimation of winds to jets associated with compact astrophysical objects such as AGN and µQuasars.All such outflows may be considered to a first approximation as ideal MHD plasmas escaping from a rotating and magnetized accretion disk with a magnetosphere around a central black hole. A crucial ingredient for a correct modelling of the steady state problem is to place the appropriate boundary conditions, by taking into account how information can propagate through the outflow and ensuring, e.g., that shocks produced via the interaction of the flow with the external medium do not affect the overall structure. As an example underlining the role of setting the correct boundary conditions, we make the analogy of the critical surfaces in the steady and axisymmetric MHD problem with the event horizon and ergosphere of a rotating black hole in relativity.We discuss the acceleration of the outflow, by gas, radiation, or wave pressure gradients and also by magnetic mechanisms, showing the important role played by the disk corona in the vicinity of the black hole. Pressure and magnetic confinement both may also play a role in confining the outflow, although magnetic hoop stress confinement is likely to be a rather dominant process in tightly collimated outflows. The possible asymptotical morphology that jets achieve and the instabilities which are likely to explain the observed structures but do not prevent jets to possess toroidal magnetic fields are also reviewed.Finally, it is proposed that in a space where the two main variables are the energy of the magnetic rotator and the angle between the line of sight and the ejection axis, some observed characteristics of AGN jets can be understood. A criterion for the transition of the morphologies of the outflows from highly collimated jets to uncollimated winds is given. It is based on the analysis of a particular class of exact solutions and may somehow generalize other earlier suggestions, such as the spinning of the black hole, the fueling of the central object, or the effects of the environment.Thus, while the horizontal AGN classification from Type 0 to Types 1 and 2 may well be an orientation effect -i.e. a dependence on the viewing angle between the source axis and the observer as in the standard model -the vertical AGN classification with uncollimated outflows (radio-quiet sources) and collimated outflows (radio-loud sources) depends both, on the efficiency of the magnetic rotator and the environment in which the outflows propagate.

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Jets from Time‐dependent Accretion Flows onto a Black Hole

Cited by 27 publications

References 20 publications

Standing Shock Instability in Advection-Dominated Accretion Flows

Standing Shock Instability in Advection-Dominated Accretion Flows

General relativistic numerical simulation of sub-Keplerian transonic accretion flows on to black holes: Schwarzschild space–time

Jet Formation and Collimation

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