Isothermal Shocks in Fully Relativistic Accretion Disks
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**Session 82 -- Relativistic Astrophysics**
*Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)*

## [82.01] Isothermal Shocks in Fully Relativistic Accretion Disks

*R. Yang, M. Kafatos and P. A. Becker (George Mason University)*
The coupled hydrodynamic equations governing equatorial flows in
thin disk accretion in the Schwarzschild metric are developed and studied
under isothermal conditions. The transonic solutions representing physically
allowed accretion onto black holes and the location of the sonic point are
investigated. For a certain range of angular momentum, there exist two
physical sonic points. A shock can occur between the two sonic points.
The entire solution with a shock still satisfies the condition for black
hole accretion, which requires supersonic flow near the black hole horizon.

The jump condition across the shock will be modified by the relativistic
effects only when the sound speed is comparable to the speed of light.
The necessary condition for the presence of a shock is also changed from
the classical condition $M>1$ where $M$ is the Mach number to the relativistic
condition $M>M_{c}$ where $M_{c}>1$ is a value depending on the ratio of the
sound speed to the speed of light. Stability analysis shows that only one of
the two possible shocks between the two sonic points is stable. Isothermal
shocks are used to explain the QPO behavior in black hole candidates such as
Cygnus X-1, Nova Muscae and GX339-4.

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