Hydrodynamic instability of accretion flows and wind flows with standing shock waves. II - Necessary and sufficient condition for axisymmetric instability

Details Hydrodynamic instability of accretion flows and wind flows with standing shock waves. II - Necessary and sufficient condition for axisymmetric instability Hydrodynamic instability of accretion flows and wind flows with standing shock waves. II - Necessary and sufficient condition for axisymmetric instability

Apr 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pasj...45..167n&link_type=abstract

PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 45, no. 2, p. 167-177.

Astronomy and Astrophysics

Astronomy

12

Accretion Disks, Flow Stability, Magnetohydrodynamic Flow, Shock Waves, Standing Waves, Stellar Winds, Black Holes (Astronomy), Rotating Fluids, Transonic Flow

Scientific paper

We have found a new instability which occurs in accretion flows onto (or wind flows from) a compact object with an axisymmetric standing shock wave. It is an axisymmetric instability which is driven if and only if the fluid decelerates at the preshock side of a shock surface; its physical origin is energy input through a displacement of the shock surface. We furthermore obtained upper and lower bounds on the growth rate, which are of the same order of magnitude. These results indicate that the black hole accretion flow of rotating fluids is subjected to an instability and, thus, cannot remain stationary if a standing shock wave exists in close proximity to the central black hole, since such a flow decelerates at the preshock side due to the centrifugal force. The time scale of this instability was estimated to be several hours for massive black holes in galactic centers, and several milliseconds for black hole candidates. It is, therefore, suggested that instabilities can cause fast changes, or variations, in the observed luminosity of active objects.

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