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Title: Thermal stability of a thin disk with magnetically driven winds

The absence of thermal instability in the high/soft state of black hole X-ray binaries, in disagreement with the standard thin disk theory, has been a long-standing riddle for theoretical astronomers. We have tried to resolve this question by studying the thermal stability of a thin disk with magnetically driven winds in the M-dot −Σ plane. It is found that disk winds can greatly decrease the disk temperature and thus help the disk become more stable at a given accretion rate. The critical accretion rate, M-dot {sub crit}, corresponding to the thermal instability threshold, is significantly increased in the presence of disk winds. For α = 0.01 and B {sub φ} = 10B {sub p}, the disk is quite stable even for a very weak initial poloidal magnetic field [β{sub p,0}∼2000,β{sub p}=(P{sub gas}+P{sub rad})/(B{sub p}{sup 2}/8π)]. However, when B {sub φ} = B {sub p} or B {sub φ} = 0.1B {sub p}, a somewhat stronger (but still weak) field (β{sub p,} {sub 0} ∼ 200 or β{sub p,} {sub 0} ∼ 20) is required to make the disk stable. Nevertheless, despite the great increase of M-dot {sub crit}, the luminosity threshold, corresponding to instability, remains almost constant or decreases slowlymore » with increasing M-dot {sub crit} due to decreased gas temperature. The advection and diffusion timescales of the large-scale magnetic field threading the disk are also investigated in this work. We find that the advection timescale can be smaller than the diffusion timescale in a disk with winds, because the disk winds take away most of the gravitational energy released in the disk, resulting in the decrease of the magnetic diffusivity η and the increase of the diffusion timescale.« less
Authors:
 [1] ;  [2]
  1. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai, 200030 (China)
  2. JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309 (United States)
Publication Date:
OSTI Identifier:
22357045
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 786; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ADVECTION; BLACK HOLES; DIFFUSION; INSTABILITY; LUMINOSITY; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; STABILITY; X RADIATION