Accretion Disks Around Black Holes in Compact Binaries


Principal Investigator

James Murray

Department of Mathematics,

School of Mathematical Sciences

Accretion discs are flattened, rotating gas structures that surround many astrophysical objects. Through
various dissipative processes, the potential energy of the gas is converted to heat, allowing the gas to spiral slowly in to the central object. In this project we are studying both the steady state, and the time-dependent behaviour of accretion discs in black hole binaries. We are using a numerical approach based on simulations with a Smooth Particle Hydrodynamics (SPH) code. Our objectives are: to understand observed spectra of these systems; and later on to extend our study to the disc around the black hole at the centre of our galaxy.



Lilia Ferrario

Dayal Wickramasinghe

Department of Mathematics,

School of Mathematical Sciences


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What are the results to date and the future of this work?

We (Murray & Armitage, MNRAS, 1997, submitted) have investigated the importance of tidal resonance in generating warps or tilts in accretion discs in binary systems. We found dynamical forces to be too weak to generate a tilt in a fluid disc, but strong enough to disturb a disc of non-interacting particles.

We also (Armitage & Murray) completed simulations to explain spiral structure observed in the accretion disc of IP Pegasi. This system is a close binary composed of a white dwarf with a low mass stellar companion. This work is now being extended to systems in which the accretion disc is partially disrupted by magnetic fields.

Murray, Ferrario and Wickramasinghe have completed several simulations of optically thin, bremsstrahlung cooled discs. The simulations show the discs to be thermally unstable. Further simulations are planned with optically thin cooling laws valid for larger temperature ranges.

What computational techniques are used?

The SPH code being used is described in detail in Murray, 1996, Monthly Notices of the Royal Astronomical Society, 279, pp 402-414. A typical calculation must run for several viscous time scales whilst accurately following motion on the much shorter time scale imposed by the gravitational potential of the binary star system. Such calculations typically take approximately one or two weeks on a DEC Alpha AXP 3000/500S work station.

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