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Krzysztof Roszkowski

Publications and source records attributed to Krzysztof Roszkowski.

7 recordsLinked to original sources
arXiv2009

Supersonic and subsonic flows in general relativistic radiation hydrodynamics

We analyze stationary accretion of selfgravitating gas onto a compact center within general-relativistic radiation hydrodynamics. Spherical symmetry and thin gas approximation are assumed. Numerical investigation shows that transonic flows exist for small redshifts and they cease to exist for high redshifts and high luminosities. There exist two branches of flows (subsonic or supersonic) that originate at a bifurcation point and that embrace the set of subsonic solutions. The morphology of the set of subsonic solutions is essentially independent of redshifts and flows that belong to their boundary provide estimates of the gas abundance of subsonic solutions. It appears that prescribed boundary data guarantee uniqueness only of the bifurcation point, and that the latter has maximal luminosity.

astro-ph↗
arXiv2008

Luminosity, redshift and gas abundance in general relativistic radiation hydrodynamics

Quasi-stationary flows of gas accreting onto a compact center are analyzed in the framework of general-relativistic radiation hydrodynamics, under assumptions of spherical symmetry and thin gas approximation. Numerical investigation shows that luminosity, redshift and gas abundance are correlated. The gas can constitute up to one third of the total mass of brightest low-redshift sources, but its abundance goes down to 1/30 for sources with luminosities close to the Eddington limit.

gr-qc↗
arXiv2006

Gravastars and bifurcation in quasistationary accretion

We investigate the newtonian stationary accretion of a polytropic perfect fluid onto a central body with a hard surface. The selfgravitation of the fluid and its interaction with luminosity is included in the model. We find that for a given luminosity, asymptotic mass and temperature of the fluid there exist two solutions with different cores.

astro-ph↗
arXiv2006

Luminosity, selfgravitation and nonuniqueness of stationary accretion

We investigate newtonian description of accreting compact bodies with hard surfaces, including luminosity and selfgravitation of polytropic perfect fluids. This nonlinear integro-differential problem reduces, under appropriate boundary conditions, to an algebraic relation between luminosity and the gas abundance in stationary spherically symmetric flows. There exist, for a given luminosity, asymptotic mass and the asymptotic temperature, two sub-critical solutions that bifurcate from a critical point. They differ by the fluid content and the mass of the compact centre.

astro-ph↗
arXiv2006

Nonuniqueness of stationary accretion in the Shakura model

We investigate the accretion onto luminous bodies with hard surfaces within the framework of newtonian theory. The accreting gases are assumed to be polytropes and their selfgravitation is included. A remarkable feature of the model is that under proper boundary conditions some parameters of the sonic point are the same as in the Bondi model and the relation between luminosity and the gas abundance reduces to an algebraic relation. All that holds under assumptions of stationarity and spherical symmetric. Assuming data that are required for the complete specification of the system, one finds that generically for a given luminosity there exist two solutions with different compact cores.

astro-ph↗
arXiv2003

Embedding spherical spacelike slices in a Schwarzschild solution

Given a spherical spacelike three-geometry, there exists a very simple algebraic condition which tells us whether, and in which, Schwarzschild solution this geometry can be smoothly embedded. One can use this result to show that any given Schwarzschild solution covers a significant subset of spherical superspace and these subsets form a sequence of nested domains as the Schwarzschild mass increases. This also demonstrates that spherical data offer an immediate counter example to the thick sandwich `theorem'.

gr-qc↗