Numerical simulation of vertical oscillations in an axisymmetric thick accretion flow around a black hole

Abstract

We study time evolution of rotating, axisymmetric, two dimensional inviscid accretion flows around black holes using a grid based finite difference method. We do not use reflection symmetry on the equatorial plane in order to inspect if the disk along with the centrifugal barrier oscillated vertically. In the inviscid limit, we find that the CENtrifugal pressure supported BOundary Layer (CENBOL) is oscillating vertically, more so, when the specific angular momentum is higher. As a result, the rate of outflow produced from the CENBOL, also oscillates. Indeed, the outflow rates in the upper half and the lower half are found to be anti-correlated. We repeat the exercise for a series of specific angular momentum λ of the flow in order to demonstrate effects of the centrifugal force on this interesting behaviour. We find that, as predicted in theoretical models of disks in vertical equilibrium, the CENBOL is produced only when the centrifugal force is significant and more specifically, when λ > 1.5. Outflow rate itself is found to increase with λ as well and so is the oscillation amplitude. The cause of oscillation appears to be due to the interaction among the back flow from the centrifugal barrier, the outflowing winds and the inflow. For low angular momentum, the back flow as well as the oscillation are missing. To our knowledge, this is the first time that such an oscillating solution is found with an well-tested grid based finite difference code and such a solution could be yet another reason of why Quasi-Periodic Oscillations should be observed in black hole candidates which are accreting low angular momentum transonic flows.

Shocks in the relativistic transonic accretion with low angular momentum

“…Such models were also studied by hydrodynamical numerical simulations in the pseudo-Newtonian description of gravity e.g. by Giri et al (2010); Giri & Chakrabarti (2013); Deb et al (2016).…”

Dynamics of Magnetic Flux Tubes in an Advective Flow around a Black Hole

“…The specific energy of the injected matter remains constant since we have not considered any radiative cooling process. For the detail description of the numerical setup for the disc simulation refer to Deb, Giri, Chakrabarti (2016). For schemes, basic properties of the code, and different test results, please refer to Harten (1983), RCM97 andRyu et al (1995).…”

“…10 and thus acceleration of jets/outflows by the field lines injected with similar initial strength was reduced. dependent accretion after removing the reflection symmetry (Deb et al 2016) condition as used in earlier purely hydrodynamic simulations (GC10). We also answered whether these magnetic flux tubes aid in the acceleration and collimation of the jets or not.…”

An Exponential Shape Function for Wormholes in Modified Gravity*

“…We will consider 𝑓 (𝑅, 𝑇 ) = 𝑅+2𝜆𝑇 , which was assumed as the functional form for the function 𝑓 (𝑅, 𝑇 ) in several approaches such as Refs. [33][34][35][36][37][38] among many others. The considered form is the simplest one, which reduces to general relativity for the choice of 𝜆 = 0.…”