Vertical Structure of Gas Pressure-dominated Accretion Disks with Local Dissipation of Turbulence and Radiative Transport

By Shigenobu Hirose, Julian Krolik, James M. Stone. 2005

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We calculate the vertical structure of a local patch of an accretion disk in which heating by dissipation of MRI-driven MHD turbulence is balanced by radiative cooling. Heating, radiative transport, and cooling are computed self-consistently with the structure by solving the equations of radiation MHD in the shearing-box approximation. Using a fully three-dimensional and energy-conserving code, we compute the structure of this disk segment over a span of more than five cooling times. After a brief relaxation period, a statistically steady state develops. Measuring height above the midplane in units of the scale height predicted by a Shakura-Sunyaev model, we find that magnetic pressure causes the disk atmosphere to stretch upward, with the photosphere rising to ≃7H, in contrast to the ≃3H predicted by conventional analytic models. This more extended structure, as well as fluctuations in the height of the photosphere, may lead to departures from Planckian form in the emergent spectra. Dissipation is distributed across the region within ≃3H of the midplane but is very weak at greater altitudes. As a result, the temperature deep in the disk interior is less than that expected when all heat is generated in the midplane. With only occasional exceptions, the gas temperature stays very close to the radiation temperature, even above the photosphere. Because fluctuations in the dissipation are particularly strong away from the midplane, the emergent radiation flux can track dissipation fluctuations with a lag that is only 0.1-0.2 times the mean cooling time of the disk. Long-timescale asymmetries in the dissipation distribution can also cause significant asymmetry in the flux emerging from the top and bottom surfaces of the disk. Radiative diffusion dominates Poynting flux in the vertical energy flow throughout the disk.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/6596e5e5d7deae868be761368a36f1a1b076bf1b

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Citations in the corpus

Delayed outflows from black hole accretion tori following neutron star binary coalescence (2013, background): “However, if an even larger fraction of the dissipation occurs in the disk corona in more realistic magnetized disks (e.g. Hirose et al. 2006), then the dominance of ‘viscous’-driven (low Ye) polar outflows may turn out to be a robust feature of the launching mechanism.”
ASSESSING QUANTITATIVE RESULTS IN ACCRETION SIMULATIONS: FROM LOCAL TO GLOBAL (2011, background): “In the shearing box simulations of Hirose et al. (2006), the local rate of this sort of dissipation scales ∝ |J|1.1 for electric current density J.”
LOCAL STUDY OF ACCRETION DISKS WITH A STRONG VERTICAL MAGNETIC FIELD: MAGNETOROTATIONAL INSTABILITY AND DISK OUTFLOW (2012, background): “We can further compare our run B4 with zero net vertical flux stratified MRI simulations (Stone et al. 1996; Miller & Stone 2000; Guan & Gammie 2011; Simon et al. 2012), where the slope of the wing is further steeper.”
Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers (2017, background): “…form of these two effects depends on the way the process is modeled (i.e. α viscosity), the overall contribution to the disk evolution is generic (e.g., magnetohydrodynamic turbulence also heats up the gas, but with a different spatial distribution than shear viscosity; e.g., Hirose et al. 2006).”
GLOBAL STRUCTURE OF THREE DISTINCT ACCRETION FLOWS AND OUTFLOWS AROUND BLACK HOLES FROM TWO-DIMENSIONAL RADIATION-MAGNETOHYDRODYNAMIC SIMULATIONS (2011, methodology): “In fact, Hirose et al. (2006) showed that the magnetic energy and the dissipation rate are nearly constant across the equatorial plane by simulations without employing the equatorial-plane symmetries.”
Global Radiation-Magnetohydrodynamic Simulations of Black-Hole Accretion Flow and Outflow: Unified Model of Three States (2009, methodology): “Such simulations were attempted in the past (e.g., Turner et al. 2003; Hirose et al. 2006), but these are restricted to local simulations performed under the shearing-box approximations and, hence, global coupling of magnetic fields was artificially quenched there.”
Three-dimensional GRMHD Simulations of Neutrino-cooled Accretion Disks from Neutron Star Mergers (2017, background): “…energy generated by viscosity is locally dissipated in proportion to the gas density, numerical simulations of MHD disks show that a disproportionally large fraction of their “heating” occurs nonlocally through reconnection in low-density coronal regions (Hirose et al. 2006; Jiang et al. 2014a).”
ZONAL FLOWS AND LONG-LIVED AXISYMMETRIC PRESSURE BUMPS IN MAGNETOROTATIONAL TURBULENCE (2008, methodology): “Similar buoyancy waves are seen in the simulations by Brandenburg et al. (1995), Miller & Stone (2000) and Hirose et al. (2006).”
A GLOBAL THREE-DIMENSIONAL RADIATION MAGNETO-HYDRODYNAMIC SIMULATION OF SUPER-EDDINGTON ACCRETION DISKS (2014, background): “Properties of the saturation state of MRI in both gas pressure and radiation pressure dominated regimes have been studied extensively with local shearing box simulations (Stone et al. 1996; Turner 2004; Hirose et al. 2006, 2009b,a; Jiang et al. 2013b).”
SUSTAINED MAGNETOROTATIONAL TURBULENCE IN LOCAL SIMULATIONS OF STRATIFIED DISKS WITH ZERO NET MAGNETIC FLUX (2009, background): “Such questions are generally better addressed by studies which include more physically realistic vertical boundary conditions (e.g., Miller & Stone 2000) and more realistic thermodynamics, including the treatment of radiation (e.g., Turner 2004; Hirose et al. 2006; Shi et al. 2009).”