A fresh look at the unstable simulations of Bondi-Hoyle-Lyttleton accretion

T Foglizzo, P Galletti, M Ruffert

Research output: Contribution to journalArticlepeer-review

Abstract

The instability of Bondi-Hoyle-Lyttleton accretion, observed in numerical simulations, is analyzed through known physical mechanisms and possible numerical artefacts. The mechanisms of the longitudinal and transverse instabilities, established within the accretion line model, are clarified. They cannot account for the instability of BHL accretion at moderate Mach number when the pressure forces within the shock cone are taken into account. The advective-acoustic instability is considered in the context of BHL accretion when the shock is detached from the accretor. This mechanism naturally explains the stability of the flow when the shock is weak, and the instability when the accretor is small. In particular, it is a robust proof of the instability of 3D accretion when gamma= 5/3 if the accretor is small enough, even for moderate shock strength ( M similar to 3). The numerical artefacts that may be present in existing numerical simulations are reviewed, with particular attention paid to the advection of entropy/vorticity perturbations and the artificial acoustic feedback from the accretor boundary condition. Several numerical tests are proposed to test these mechanisms.

Original languageEnglish
Pages (from-to)397-411
Number of pages15
JournalAstronomy & Astrophysics
Volume435
Issue number2
DOIs
Publication statusPublished - May 2005

Keywords

  • accretion, accretion disks
  • hydrodynamics
  • instabilities
  • shock waves
  • black hole physics
  • ENTROPIC-ACOUSTIC INSTABILITY
  • LINE-DRIVEN INSTABILITY
  • MOVING BLACK-HOLE
  • WIND-ACCRETION
  • NUMERICAL SIMULATIONS
  • VELOCITY-GRADIENTS
  • COMPACT OBJECTS
  • AXISYMMETRIC ACCRETION
  • INHOMOGENEOUS-MEDIUM
  • STABILITY ANALYSIS

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