Time-dependent spherically symmetric accretion onto compact x-ray sources

Journal Article · Fri Dec 15 04:00:00 EST 1978 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156682· OSTI ID:6448172

Cowie, L L; Ostriker, J P; Stark, A A

We show that preheating of spherically symmetric accreting gas flows by the emergent radiation from the accreting stars will result in time-dependent behavior for a much wider range of source parameters than was previously expected. Modeling such systems analytically and using a time-dependent hydrodynamic code, we find two distinct types of instability. For low efficiency (equivalentL/sub x//Mc/sup 2/) but high luminosity, heating inside the sonic point causes recurrent flares at relatively short intervals, the average luminosity remaining at the value that would have been expected for a stationary flow. For efficiencies greater than approx.10/sup -2.0/, heating outside the sonic point produces longer time scale variations and tends to substantially reduce the mean luminous output. The results are compared with observations of bursters and of transients, and with theories of galactic nuclei based on accretion of gas onto massive black holes. Spherically symmetric models for bursters fail, but a variant in which the bursts are produced by infalling fragments of a Rayleigh-Taylor unstable shell around a rather massive black hole is possible. The soft spectrum transient sources may be related to condensed objects orbiting late-type evolved stars losing mass via low-velocity winds; if so, an IR excess and opitcal emission lines should be seen. X-ray flares in the hard-spectrum extragalactic sources, if they exist, will accelerate gas to velocities of 3,000--10,000 km s/sup -1/.

• Research Organization: Princeton University Observatory
• OSTI ID: 6448172
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 226:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics & Cosmology-- Quasi-Stellar
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BLACK HOLES
COOLING
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DIFFERENTIAL EQUATIONS
EQUATIONS
EQUATIONS OF MOTION
FLUID FLOW
FLUID MECHANICS
GALAXIES
HYDRODYNAMICS
INSTABILITY
LUMINOSITY
MATHEMATICAL MODELS
MECHANICS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIVE COOLING
RAYLEIGH-TAYLOR INSTABILITY
STAR ACCRETION
STAR EVOLUTION
STAR MODELS
STELLAR FLARES
TIME DEPENDENCE