Black hole mergers: can gas discs solve the 'final parsec' problem?     

G. Lodato  S. Nayakshin  A. R. King  J. E. Pringle 《Monthly notices of the Royal Astronomical Society》2009,398(3):1392-1402

We compute the effect of an orbiting gas disc in promoting the coalescence of a central supermassive black hole binary. Unlike earlier studies, we consider a finite mass of gas with explicit time dependence: we do not assume that the gas necessarily adopts a steady state or a spatially constant accretion rate, i.e. that the merging black hole was somehow inserted into a pre-existing accretion disc. We consider the tidal torque of the binary on the disc, and the binary's gravitational radiation. We study the effects of star formation in the gas disc in a simple energy feedback framework.
The disc spectrum differs in detail from that found before. In particular, tidal torques from the secondary black hole heat the edges of the gap, creating bright rims around the secondary. These rims do not in practice have uniform brightness either in azimuth or time, but can on average account for as much as 50 per cent of the integrated light from the disc. This may lead to detectable high-photon-energy variability on the relatively long orbital time-scale of the secondary black hole, and thus offer a prospective signature of a coalescing black hole binary.
We also find that the disc can drive the binary to merger on a reasonable time-scale only if its mass is at least comparable with that of the secondary black hole, and if the initial binary separation is relatively small, i.e.   a ₀≲ 0.05  pc. Star formation complicates the merger further by removing mass from the disc. In the feedback model we consider, this sets an effective limit to the disc mass. As a result, binary merging is unlikely unless the black hole mass ratio is ≲0.001. Gas discs thus appear not to be an effective solution to the 'last parsec' problem for a significant class of mergers.  相似文献   

Evolution of astrophysical jets generated by a vortex mechanism     

M. G. Abrahamyan 《Astrophysics》2009,52(1):119-131

The nonlinear dynamics of a rotating jet is examined following its ejection from a compact gravitating object by a vortex mechanism. A scenario is described in which a dense stream expands and is subsequently transformed into a nonstationary vortex consisting of a cylindrical core and a “sheath.” At this stage of development, a converging radial flow of matter in the differentially rotating nonuniform sheath collimates the jet and speeds up the rotation of the core, as well as the flow of matter along the jet, in accordance with a power law or “explosive” instability, until the velocity discontinuity at the surface of the core approaches the sound speed. Flows of this type have low energy dissipation and can serve as unique channels for the acceleration and collimation of jet eruptions from young stars, active galactic nuclei, and quasars. Translated from Astrofizika, Vol. 52, No. 1, pp. 135–145 (February 2009).  相似文献   

The Classification and Model of Coalbed Methane Reservoirs   总被引：8，自引：0，他引：8  

SU Xianbo  LIN Xiaoying  SONG Yan  ZHAO Mengjun Henan University of the Sciences  Jiaozuo  Henan Research Institute of Petroleum Exploration  Development  PetroChin  Beijing 《《地质学报》英文版》2004,78(3):662-666

Coalbed methane has been explored in many basins worldwide for 30 years, and has been developed commercially in some of the basins. Many researchers have described the characteristics of coalbed methane geology and technology systematically. According to these investigations, a coalbed methane reservoir can be defined: "a coal seam that contains some coalbed methane and is isolated from other fluid units is called a coalbed methane reservoir". On the basis of anatomization, analysis, and comparison of the typical coalbed methane reservoirs, coalbed methane reservoirs can be divided into two classes: the hydrodynamic sealing coalbed methane reservoirs and the self-sealing coalbed methane reservoirs. The former can be further divided into two sub-classes: the hydrodynamic capping coalbed methane reservoirs, which can be divided into five types and the hydrodynamic driving coalbed methane reservoirs, which can be divided into three types. The latter can be divided into three types. Currently, hydrodynamic s  相似文献   

Modelling solar atmospheric gravity oscillation modes     

B. Pintr 《Astronomische Nachrichten》2008,329(5):503-507

Solar oscillations are investigated in a one‐dimensional hydrodynamic plane‐parallel model with an atmosphere. Besides the acoustic pressure (p) modes, the fundamental (f) and Lamb mode, another set of eigenmodes, a group of atmospheric gravity (g) modes, is found in the low‐frequency region of the spectrum. Their frequencies and spatial behaviour are studied. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

On the dynamics of a twisted disc immersed in a radiation field     

P. B. Ivanov  J. C. B. Papaloizou 《Monthly notices of the Royal Astronomical Society》2008,384(1):123-149

  相似文献   

Radiation hydrodynamics in Kerr space–time: equations without coordinate singularity at the event horizon     

Rohta Takahashi 《Monthly notices of the Royal Astronomical Society》2008,383(3):1155-1165

  相似文献   

Numerical simulations of type III planetary migration – II. Inward migration of massive planets     

A. Pepli&#;ski  P. Artymowicz  G. Mellema 《Monthly notices of the Royal Astronomical Society》2008,386(1):179-198

We present a numerical study of rapid, so-called type III migration for Jupiter-sized planets embedded in a protoplanetary disc. We limit ourselves to the case of inward migration, and study in detail its evolution and physics, concentrating on the structure of the corotation and circumplanetary regions, and processes for stopping migration. We also consider the dependence of the migration behaviour on several key parameters. We perform this study using the results of global, two-dimensional hydrodynamical simulations with adaptive mesh refinement. The initial conditions are chosen to satisfy the condition for rapid inward migration. We find that type III migration can be divided into two regimes, fast and slow. The structure of the co-orbital region, mass accumulation rate and migration behaviour differ between these two regimes. All our simulations show a transition from the fast to the slow regime, ending type III migration well before reaching the star. The stopping radius is found to be larger for more massive planets and less massive discs. A sharp density drop is also found to be an efficient stopping mechanism. In the fast migration regime the migration rate and induced eccentricity are lower for less massive discs, but almost do not depend on planet mass. Eccentricity is damped on the migration time-scale.  相似文献   

Simulations of spiral galaxies with an active potential: molecular cloud formation and gas dynamics     

C. L. Dobbs  I. A. Bonnell 《Monthly notices of the Royal Astronomical Society》2008,385(4):1893-1902

We describe simulations of the response of a gaseous disc to an active spiral potential. The potential is derived from an N -body calculation and leads to a multi-armed time-evolving pattern. The gas forms long spiral arms typical of grand-design galaxies, although the spiral pattern is asymmetric. The primary difference from a grand-design spiral galaxy, which has a consistent two-/four-armed pattern, is that instead of passing through the spiral arms, gas generally falls into a developing potential minimum and is released only when the local minimum dissolves. In this case, the densest gas is coincident with the spiral potential, rather than offset as in the grand-design spirals. We would therefore expect no offset between the spiral shock and star formation, and no obvious corotation radius. Spurs which occur in grand-design spirals when large clumps are sheared off leaving the spiral arms, are rare in the active, time-evolving spiral reported here. Instead, large branches are formed from spiral arms when the underlying spiral potential is dissolving due to the N -body dynamics. We find that the molecular cloud mass spectrum for the active potential is similar to that for clouds in grand-design calculations, depending primarily on the ambient pressure rather than the nature of the potential. The largest molecular clouds occur when spiral arms collide, rather than by agglomeration within a spiral arm.  相似文献   

Radiative bubbles blown by slow stellar winds     

Christopher D. Matzner  Ruben Krasnopolsky 《Monthly notices of the Royal Astronomical Society》2008,386(2):903-908

  相似文献   

Hydrodynamical simulations of Galactic fountains – I. Evolution of single fountains     

C. Melioli  F. Brighenti  A. D'Ercole  E. M. de Gouveia Dal Pino 《Monthly notices of the Royal Astronomical Society》2008,388(2):573-586

The ejection of the gas out of the disc in late-type galaxies is related to star formation and is due mainly to Type II supernovae. In this paper, we studied in detail the development of the Galactic fountains in order to understand their dynamical evolution and their influence on the redistribution of the freshly delivered metals over the disc. To this aim, we performed a number of 3D hydrodynamical radiative cooling simulations of the gas in the Milky Way where the whole Galaxy structure, the Galactic differential rotation and the supernova explosions generated by a single OB association are considered. A typical fountain powered by 100 Type II supernovae may eject material up to ∼2 kpc which than collapses back mostly in the form of dense, cold clouds and filaments. The majority of the gas lifted up by the fountains falls back on the disc remaining within a radial distance  Δ R = 0.5 kpc  from the place where the fountain originated. This localized circulation of disc gas does not influence the radial chemical gradients on large scale, as required by the chemical models of the Milky Way which reproduce the metallicity distribution without invoking large fluxes of metals. Simulations of multiple fountains fuelled by Type II supernovae of different OB associations will be presented in a companion paper.  相似文献