Computation of Mass Outflow Rate from Relativistic Quasi-Spherical Accretion onto Black Holes

We compute mass outflow rate $R_{\dot m}$ from relativistic matter accreting quasi-spherically onto Schwarzschild black holes. Taking the pair-plasma pressure mediated shock surface as the {\it effective} boundary layer (of the black hole) from where bulk of the outflow is assumed to be generated, computation of this rate is done using combinations of exact transonic inflow and outflow solutions. We find that $R_{\dot m}$ depends on the initial parameters of the flow, the polytropic index of matter, the degree of compression of matter near the shock surface and on the location of the shock surface itself. We thus not only study the variation of the mass outflow rate as a function of various physical parameters governing the problem but also provide a sufficiently plausible estimation of this rate.Comment: 6 twocoloumn pages with 5 figures. mn.sty used. Accepted for publication in MNRA

Modal Selection for Inclined Darcy-Benard Convection in a Rectangular Cavity

Nonlinear free convection in an inclined rectangular porous cavity heated from below has been studied using a two-dimensional spectral decomposition. The code uses pseudo-arclength continuation to follow solution curves around fold bifurcations. The evolution with inclination of the pattern of convection is complicated and it relies strongly on both the Darcy-Rayleigh number and the aspect ratio of the cavity. When the inclination is large it is generally true that only one cell appears, and that it has a circulation that is consistent with the direction of the buoyancy forces along the heated and cooled boundaries. However, as the inclination decreases back towards the horizontal, this unicellular pattern evolves, sometimes initially via fold bifurcations, into patterns with different numbers of cells. Such evolutions always conserve the parity of the number of cells (such as one cell becoming three and then five, or two cells becoming four), but bifurcations also arise between patterns with different parities. These phenomena are illustrated using a suitable selection of solution curves that show the dependence of the Nusselt number on the inclination

Nonradial and nonpolytropic astrophysical outflows VIII. A GRMHD generalization for relativistic jets

Steady axisymmetric outflows originating at the hot coronal magnetosphere of a Schwarzschild black hole and surrounding accretion disk are studied in the framework of general relativistic magnetohydrodynamics (GRMHD). The assumption of meridional self-similarity is adopted for the construction of semi-analytical solutions of the GRMHD equations describing outflows close to the polar axis. In addition, it is assumed that relativistic effects related to the rotation of the black hole and the plasma are negligible compared to the gravitational and other energetic terms. The constructed model allows us to extend previous MHD studies for coronal winds from young stars to spine jets from Active Galactic Nuclei surrounded by disk-driven outflows. The outflows are thermally driven and magnetically or thermally collimated. The collimation depends critically on an energetic integral measuring the efficiency of the magnetic rotator, similarly to the non relativistic case. It is also shown that relativistic effects affect quantitatively the depth of the gravitational well and the coronal temperature distribution in the launching region of the outflow. Similarly to previous analytical and numerical studies, relativistic effects tend to increase the efficiency of the thermal driving but reduce the effect of magnetic self-collimation.Comment: 20 page, Accepted in A&A 10/10/200

Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black Holes

We compute the nucleosynthesis of materials inside advective disks around black holes. We show that composition of incoming matter can change significantly depending on the accretion rate and accretion disks. These works are improvements on the earlier works in thick accretion disks of Chakrabarti, Jin & Arnett (1987) in presence of advection in the flow.Comment: Latex pages including figures. Kluwer Style files included. Appearing in `Observational Evidence for Black Holes in the Universe', ed. Sandip K. Chakrabarti, Kluwer Academic Publishers (DORDRECHT: Holland

Two temperature viscous accretion flows around rotating black holes: Description of under-fed systems to ultra-luminous X-ray sources

We discuss two temperature accretion disk flows around rotating black holes. As we know that to explain observed hard X-rays the choice of Keplerian angular momentum profile is not unique, we consider the sub-Keplerian regime of the disk. Without any strict knowledge of the magnetic field structure, we assume the cooling mechanism is dominated by bremsstrahlung process. We show that in a range of Shakura-Sunyaev viscosity parameter 0.2\gsim\alpha\gsim0.0005, flow behavior varies widely, particularly by means of the size of disk, efficiency of cooling and corresponding temperatures of ions and electrons. We also show that the disk around a rotating black hole is hotter compared to that around a Schwarzschild black hole, rendering a larger difference between ion and electron temperatures in the former case. With all the theoretical solutions in hand, finally we reproduce the observed luminosities ($L$) of two extreme cases -- the under-fed AGNs and quasars (e.g. Sgr $A^*$) with L\gsim 10^{33} erg/sec to ultra-luminous X-ray sources with $L\sim 10^{41}$ erg/sec, at different combinations of mass accretion rate, ratio of specific heats, Shakura-Sunyaev viscosity parameter and Kerr parameter, and conclude that Sgr $A^*$ may be an intermediate spinning black hole.Comment: 21 pages including 5 figures; few typos corrected; to appear in New Astronom

Hadronic signals of deconfinement at RHIC

This article reviews (soft) hadronic signals of deconfinement and chiral symmetry restoration in hot QCD matter in the light of the results from the first three years of the experimental program at the Relativistic Heavy Ion Collider.Comment: Contribution to RBRC Scientific Articles Proceedings Series "New Discoveries at RHIC

Anisotropic AGN Outflows and Enrichment of the Intergalactic Medium

We investigate the cosmological-scale influence of outflows driven by AGNs on metal enrichment of the intergalactic medium. AGNs are located in dense cosmological structures which tend to be anisotropic. We designed a semi-analytical model for anisotropic AGN outflows which expand away along the direction of least resistance. This model was implemented into a cosmological numerical simulation algorithm for simulating the growth of large-scale structure in the universe. Using this modified algorithm, we perform a series of 9 simulations inside cosmological volumes of size $(128 h^{-1}{\rm Mpc})^3$, in a concordance $\Lambda$CDM universe, varying the opening angle of the outflows, the lifetimes of the AGNs, their kinetic fractions, and their level of clustering. For each simulation, we compute the volume fraction of the IGM enriched in metals by the outflows. The resulting enriched volume fractions are relatively small at $z \gtrsim 2.5$, and then grow rapidly afterward up to $z = 0$. We find that AGN outflows enrich from 65% to 100% of the entire universe at the present epoch, for different values of the model parameters. The enriched volume fraction depends weakly on the opening angle of the outflows. However, increasingly anisotropic outflows preferentially enrich underdense regions, a trend found more prominent at higher redshifts and decreasing at lower redshifts. The enriched volume fraction increases with increasing kinetic fraction and decreasing AGN lifetime and level of clustering.Comment: 19 pages, 16 figures, submitted. The version uploaded here does not contain Figs 5, 6 & 7, because of their large sizes. Those can be found along with the full paper at: http://www.astro.phy.ulaval.ca/staff/paramita/AllPages/Talks-Posters/Papers_Thesis/ms_AGNoutflow.pd