Yazar "Doenmez, Orhan" seçeneğine göre listele

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    Numerical simulation of small perturbation on an accretion disk due to the collision of a star with the disk near the black hole
    (SPRINGER, 2006) Doenmez, Orhan
    In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by Donmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a "star", modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body. When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the X-rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies.
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    The effects of different perturbations on the dynamics of the accretion disk around the black hole
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2007) Doenmez, Orhan
    We investigate the special cases of the formation of shocks in the accretion disks around the nonrotating (Schwarzschild) black holes in cases where one or few stars perturb the disk. We model the structure of disk with a 2D fully general relativistic hydrodynamic code and investigate a variety of cases in which the stars interacting with the disk are captured at various locations. We have found the following results: (1) if the stars perturb the disk at nonsymmetric locations, a moving one-armed spiral shock wave is produced and it destroys the disk eventually; (2) if the disk is perturbed by a single star located close to the black hole, a standing shock wave is produced while the disk becomes an accretion tori; (3) if the disk is perturbed by stars at symmetric locations, moving two-armed spiral shock waves are produced while the disk reaches a steady state; (4) continuous injection of matter into the stable disk produces a standing shock wave behind the black hole. Our outcomes reinforce the view that different perturbations on the stable accretion disk carry out different types of shock waves which produce Quasi-Periodic Oscillation (QPO) phenomena in galactic black hole candidates and it is observed as a X-ray.
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    The numerical simulation of perturbed accretion disk around the massive black hole
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2006) Doenmez, Orhan
    The dynamical evolution of star-disk interaction containing a massive black hole is examined in a region in which physical perturbation dominates other processes and strong gravitational region dominates the potential. The numerical simulation of accretion disk around the black hole is modeled when star is captured by it. When the accretion disk, in steady state or not, is perturbed by the star, the disk around the black hole is destroyed by the star-disk interaction. Destroyed accretion disk creates a spiral shock wave and it causes loss of angular momentum. Finally, because of losing angular momentum, gas starts falling into the black hole. At the same time, X-ray is emitted by accretion disk during the unstable cases. The massive black hole may be created as a consequence of interaction.