Magnetorotational Instability in Protoplanetary Disks. II. Ionization State and Unstable Regions

By Takayoshi Sano, S. Miyama, T. Umebayashi, T. Nakano. 2000

335 citations recorded by the source corpus.

We investigate where magnetorotational instability operates in protoplanetary disks, which can cause angular momentum transport in the disks. We investigate the spatial distribution of various charged particles and the unstable regions for a variety of models for protoplanetary disks, taking into account the recombination of ions and electrons at grain surfaces, which is an important process in most parts of the disks. We find that for all the models there is an inner region that is magnetorotationally stable due to ohmic dissipation. This must make the accretion onto the central star nonsteady. For the model of the minimum-mass solar nebula, the critical radius, inside of which the disk is stable, is about 20 AU, and the mass accretion rate just outside the critical radius is 10-7-10-6 M☉ yr-1. The stable region is smaller in a disk of lower column density. Dust grains in protoplanetary disks may grow by mutual sticking and may sediment toward the midplane of the disks. We find that the stable region shrinks as the grain size increases or the sedimentation proceeds. Therefore, in the late evolutionary stages, protoplanetary disks can be magnetorotationally unstable even in the inner regions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e9a8072893278e6bacf8b1fce9eb8995f910e8b2

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Citations in the corpus

Toward a Deterministic Model of Planetary Formation. IV. Effects of Type I Migration (2008, background): “Protoplanets are formed in disk regions where the midplane is inactive to magnetorotational instabilities (e.g., Sano et al. 2000).”
Turbulent Mixing and the Dead Zone in Protostellar Disks (2006, methodology): “Well-mixed 0.1 m grains with the interstellar dust-to-gas mass ratio in the minimum-mass solar nebula produce a dead zone extending to about 20AU (Sano et al. 2000; Matsumura & Pudritz 2006).”
Demographics of Transition Objects (2007, background): “By reducing the small grain population in the surface layers of the disk, grain growth is expected to lead to larger ionization fractions and therefore larger surface disk columns that are susceptible to the magnetorotational instability (e.g., Sano et al. 2000).”
The ionization fraction in α models of protoplanetary discs (2001, positive): “Cosmic rays, a classical ionization source in cool gas, have also been considered as a source of ionization (Gammie 1996; Sano et al. 2000), but the low-energy particles (important for ionization) were almost certainly excluded by winds from the early solar nebula, as they are today in a far less…”
Planet-Disk Interaction and Orbital Evolution (2012, background): “Details of this layered structure depend on a large number of parameters including the sizes and abundances of dust grains (Sano et al., 2000; Ilgner & Nelson, 2006), and the intensity of external ionisation sources (Turner & Drake, 2009), in addition to the field strength and topology.”
Theory of Star Formation (2007, background): “…dust particles; if small grains are present and well-mixed, the active region is quite limited, while it can become very large if all the dust is incorporated in large particles or settles to the midplane (Sano et al., 2000; Fromang, Terquem, & Balbus, 2002; Desch, 2004; Salmeron & Wardle, 2005).”
RAPID COAGULATION OF POROUS DUST AGGREGATES OUTSIDE THE SNOW LINE: A PATHWAY TO SUCCESSFUL ICY PLANETESIMAL FORMATION (2012, background): “First, small dust particles stabilize MRI-driven turbulence because they efficiently capture ionized gas particles and thereby reduce the electric conductivity of the gas (e.g., Sano et al. 2000).”
WEAK TURBULENCE IN THE HD 163296 PROTOPLANETARY DISK REVEALED BY ALMA CO OBSERVATIONS (2015, background): “…where the ionization is insufficient to effectively couple the gas to the magnetic field, although these zones are expected to extend out to R∼ 10–30 AU (e.g., Sano et al. 2000; Dzyurkevich et al. 2013), while our measurements are most sensitive to the behavior in the outer (R> 30 AU) disk.”
Dust settling in local simulations of turbulent protoplanetary disks (2006, background): “The extent of this dead zone is very uncertain, since it depends on the ionising source and on the chemistry (Sano et al. 2000; Fromang et al. 2002; Ilgner & Nelson 2006), but its existence is likely.”
Mechanism of Magnetic Flux Loss in Molecular Clouds (2002, methodology): “Sano et al. (2000) give the empirical formulae of the momentum transfer rate coefficients for the collision of electrons with H2 molecules and with He atoms, which were obtained by T. Umebayashi (1993, private communication) by fitting to laboratory data.”
The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability. I. Local Axisymmetric Simulations (2002, methodology): “As discussed at the start of this section, this picture could be modified by the effect of dust grains (Wardle & Ng 1999; Sano et al. 2000).”
Local Magnetohydrodynamic Models of Layered Accretion Disks (2002, positive): “(The presence of small dust grains can significantly change this picture, however, and lead to much lower ionization fractions, Wardle & Ng 1999; Sano et al. 2000.”
ELECTRIC CHARGING OF DUST AGGREGATES AND ITS EFFECT ON DUST COAGULATION IN PROTOPLANETARY DISKS (2009, methodology): “This conclusion is in contrast to that of previous studies (e.g., Sano et al. 2000; Wardle 2007) which claimed that the ionization degree increases as the aggregates grow.”
NONSTEADY ACCRETION IN PROTOSTARS (2008, background): “Both calculations assume that absorption of ions and electrons by grains is unimportant, which is only true if small dust is highly depleted in the active layer (e.g., Sano et al. 2000, also Ilgner & Nelson 2006a,b,c).”
Dynamics of Protoplanetary Disks (2010, background): “…present in more refined calculations, which model reactions between large numbers of chemical species (Bai & Goodman 2009; Ilgner & Nelson 2006; Sano et al. 2000; Semenov, Wiebe & Henning 2004), though at a weaker level, because the more complex models include additional avenues for…”
Episodic accretion in magnetically layered protoplanetary discs (2001, background): “…St Andrews KY16 9SS at larger radii of r ∼ 1 AU, where the temperature is typically a few hundred K, magnetic field instabilities are suppressed by the low ionization fraction (Matsumoto & Tajima 1995; Gammie 1996; Gammie & Menou 1998; Livio 1999; Wardle 1999; Sano & Miyama 1999; Sano et al. 2000).”
A simple model for the evolution of the dust population in protoplanetary disks (2012, background): “The grain surfaces also provide the ground for chemical surface reactions (e.g., Aikawa & Nomura 2006) and electron capture, so that dust strongly influences the ionization state and possibly the turbulent state of the disk (Sano et al. 2000; Bai & Goodman 2009; Turner et al. 2010).”