Local Magnetohydrodynamic Models of Layered Accretion Disks

By T. Fleming, James M. Stone. 2002

262 citations recorded by the source corpus.

Using numerical MHD simulations, we have studied the evolution of the magnetorotational instability (MRI) in stratified accretion disks in which the ionization fraction (and therefore resistivity) varies substantially with height. This model is appropriate to dense, cold disks around protostars or dwarf nova systems, which are ionized by external irradiation of cosmic rays or high-energy photons. We find that the growth and saturation of the MRI occurs only in the upper layers of the disk where the magnetic Reynolds number exceeds a critical value; in the midplane the disk remains quiescent. The vertical Poynting flux into the "dead" central zone is small; however, velocity fluctuations in the dead zone driven by the turbulence in the active layers generate a significant Reynolds stress in the midplane. When normalized by the thermal pressure, the Reynolds stress in the midplane never drops below about 10% of the value of the Maxwell stress in the active layers, even though the Maxwell stress in the dead zone may be orders of magnitude smaller than this. Significant mass mixing occurs between the dead zone and active layers. Fluctuations in the magnetic energy in the active layers can drive vertical oscillations of the disk in models in which the ratio of the column density in the dead zone to that in the active layers is less than 10. These results have important implications for the global evolution of a layered disk; in particular, there may be residual mass inflow in the dead layer. We discuss the effects that dust in the disk may have on our results.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/bd1b0b3c4025fcad8314e4f754923b67ea6bed3a

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Citations in the corpus

Turbulent Mixing and the Dead Zone in Protostellar Disks (2006, methodology): “Similar calculations by Fleming & Stone (2003) showed still weaker midplane magnetic stresses, because the vertical boundaries were periodic or impermeable and the net radial magnetic flux remained zero.”
EMPIRICAL CONSTRAINTS ON TURBULENCE IN PROTOPLANETARY ACCRETION DISKS (2010, methodology): “This is mitigated by the use of more realistic simulation conditions including vertical stratification (e.g., Stone et al. 1996; Fleming & Stone 2003; Davis et al. 2010; Flaig et al. 2010), but the resulting dependence of α and therefore turbulent velocity fluctuations on the magnitude of the…”
On the relevance of subcritical hydrodynamic turbulence to accretion disk transport (2005, background): “The turbulent transport induced by this instability is by now characterized in a number of instances, and has been called upon even when only some fraction of the disk is ionized, as in the midplane region of YSOs inner disks – the dead-zone (Gammie 1996; Fleming & Stone 2003).”
PARTICLE CLUMPING AND PLANETESIMAL FORMATION DEPEND STRONGLY ON METALLICITY (2009, background): “Our hydrodynamical simulations offer a first approximation to dead zones with low ionization (Sano et al. 2000) where turbulent surface layers drive only weak motions in the mid-plane (Fleming & Stone 2003; Oishi et al. 2007).”
Ice Condensation as a Planet Formation Mechanism (2013, background): “However, the prescence of a dead zone can give a lowerαvalue (Fleming & Stone, 2003; Oishi & Mac Low, 2009), and there are also observations suggestingα = 10−4 in protoplanetary discs (Mulders & Dominik, 2012).”
WIND-DRIVEN ACCRETION IN PROTOPLANETARY DISKS. I. SUPPRESSION OF THE MAGNETOROTATIONAL INSTABILITY AND LAUNCHING OF THE MAGNETOCENTRIFUGAL WIND (2013, background): “In the conventional picture of layered accretion, the Ohmic dead zone region is found to be not completely static, but has random motion due to the sound waves launched from the active layers (Fleming & Stone 2003; Oishi & Mac Low 2009; Turner et al. 2010; Okuzumi & Hirose 2011).”
Dynamics of Protoplanetary Disks (2010, background): “In the vertically stratified local simulations of Fleming & Stone (2003), the mid-plane Reynolds stress in the dead zone was found to be surprisingly large – less than an order of magnitude below the Maxwell stress in an MRI-active disk.”
PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS (2009, background): “…with those found in numerical magnetohydrodynamics simulations, where the magnetorotational instability (Balbus & Hawley 1991) is the mechanism responsible for generating the anomalous turbulent viscosities (e.g., Hawley et al. 1995; Stone et al. 1996; Fleming & Stone 2003; Fromang et al. 2007).”
Forming Planetesimals in Solar and Extrasolar Nebulae (2009, background): “Our α scalings may not apply to the weak motions possibly excited by MRI-active surface layers (Gammie 1996, Fleming & Stone 2003, Oishi et al. 2007; see also Bai & Goodman 2009 for detailed estimates of the active layer thickness).”
Thanatology in protoplanetary discs - The combined influence of Ohmic, Hall, and ambipolar diffusion on dead zones (2014, methodology): “…configuration: The zero vertical-net-flux configuration has been largely explored in the past, both with unstratified (Hawley et al. 1996; Fromang & Papaloizou 2007) and stratified simulations (Brandenburg et al. 1995; Stone et al. 1996; Fleming & Stone 2003; Simon et al. 2012, 2013b).”
Planet formation bursts at the borders of the dead zone in 2D numerical simulations of circumstellar disks (2009, background): “This happens because the turbulence on the active layers induce small levels of Reynolds stress in the dead zone (Fleming & Stone 2003).”
The evolution of the water distribution in a viscous protoplanetary disk (2005, background): “This could lead to spatially heterogeneous turbulence, where the very inner and outer parts of the disk were active while the region from∼1-10 AU would be nearly dead (Gammie 1996, see however Fleming and Stone, 2003).”
Towards initial mass functions for asteroids and Kuiper Belt Objects (2010, background): “While the ultimate cause and intensity of nebula turbulence remain subjects of debate on theoretical grounds (Fleming and Stone 2003; Johnson and Gammie 2005; Turner et al 2007), observational arguments suggest it was indeed present at interesting levels throughout the primary accretion stage (Dulle”