arXiv subjects

D. Molteni

Publications and source records attributed to D. Molteni.

21 records · Page 2Linked to original sources

arXiv1997

Smoothed Particle Hydrodynamic Simulations of Viscous Accretion Discs Around Black Holes

Viscous Keplerian discs become sub-Keplerian close to a black hole since they pass through sonic points before entering into it. We study the time evolution of polytropic viscous accretion discs (both in one and two dimensional flows) using Smoothed Particle Hydrodynamics. We discover that for a large region of the parameter space, when the flow viscosity parameter is less than a critical value, standing shock waves are formed. If the viscosity is very high then the shock disappears. In the intermediate viscosity the disc oscillates very significantly in viscous time-scale. Our simulations indicate that these centrifugally supported high density region close to a black hole plays an active role in the flow dynamics, and consequently, the radiation dynamics.

astro-ph↗

arXiv1996

Numerical Simulations Of Advective Flows Around Black Holes

We present fully time-dependent solutions of accretion processes on black holes and compare them with analytical solutions. We use Smoothed Particle Hydrodynamics and Total Variation Diminishing mathods as the numerical tenchniques. Apart from steady state solutions, we also obtain time dependent results where the shock oscillates with the characteristic period of quasi-periodic oscillations (QPOs) observed in galactic and extragalactic black hole candidates. This oscillation produces 10-15% variation in the hard X-rays in galactic candidates and in soft X-rays in Extragalactic candidates.

astro-ph↗

arXiv1994

Steady state shocks in accretion disks around a Kerr black hole

Results of numerical simulations of shock solutions in a geometrical thin accretion disk around a Kerr black hole (BH) are presented. Using the smoothed particle hydrodynamics (SPH) technique, the influence of the central object is included by means of an effective potential, We first present the theory of standing shock formation in accretion disks around a Kerr black hole, and show that the results of our numerical simulation agree very well with the theoretical results. We find that the shocks in an inviscid flow are very stable. We also remove the ambiguity prevalent regarding the location and stability of shocks in adiabatic flows. Finally we sketch some of the astrophysical consequences of our findings in relation to accretion disks in Active Galactic Nuclei (AGN) and Quasars.

astro-ph↗