Article

Gas Accretion onto a Protoplanet and Formation of a Gas Giant Planet

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 02/2010; DOI:10.1111/j.1365-2966.2010.16527.x
Source: arXiv

ABSTRACT We investigate gas accretion onto a protoplanet, by considering the thermal effect of gas in three-dimensional hydrodynamical simulations, in which the wide region from a protoplanetary gas disk to a Jovian radius planet is resolved using the nested-grid method. We estimate the mass accretion rate and growth timescale of gas giant planets. The mass accretion rate increases with protoplanet mass for M_p < M_cri, while it becomes saturated or decreases for M_p > M_cri, where M_cri = 0.036 M_Jup (a_p/1AU)^0.75, and M_Jup and a_p are the Jovian mass and the orbital radius, respectively. The growth timescale of a gas giant planet or the timescale of the gas accretion onto the protoplanet is about 10^5 yr, that is two orders of magnitude shorter than the growth timescale of the solid core. The thermal effects barely affect the mass accretion rate because the gravitational energy dominates the thermal energy around the protoplanet. The mass accretion rate obtained in our local simulations agrees quantitatively well with those obtained in global simulations with coarser spatial resolution. The mass accretion rate is mainly determined by the protoplanet mass and the property of the protoplanetary disk. We find that the mass accretion rate is correctly calculated when the Hill or Bondi radius is sufficiently resolved. Using the oligarchic growth of protoplanets, we discuss the formation timescale of gas giant planets. Comment: Accepted for publication in MNRAS. High resolution figures are available at http://www2-tap.scphys.kyoto-u.ac.jp/~machidam/astro-ph/Planet/

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    ABSTRACT: Core accretion and disk instability require giant protoplanets to form in the presence of disk gas. Protoplanet migration models generally assume disk masses low enough that the disk's self-gravity can be neglected. However, disk instability requires a disk massive enough to be marginally gravitationally unstable (MGU). Even for core accretion, a FU Orionis outburst may require a brief MGU disk phase. We present a new set of three dimensional, gravitational radiation hydrodynamics models of MGU disks with multiple protoplanets, which interact gravitationally with the disk and with each other, including disk gas mass accretion. Initial protoplanet masses are 0.01 to 10 $M_\oplus$ for core accretion models, and 0.1 to 3 $M_{Jup}$ for Nice scenario models, starting on circular orbits with radii of 6, 8, 10, or 12 AU, inside a 0.091 $M_\odot$ disk extending from 4 to 20 AU around a $1 M_\odot$ protostar. Evolutions are followed for up to $\sim$ 4000 yr and involve phases of relative stability ($e \sim$ 0.1) interspersed with chaotic phases ($e \sim$ 0.4) of orbital interchanges. The 0.01 to 10 $M_\oplus$ cores can orbit stably for $\sim$ 1000 yr: monotonic inward or outward orbital migration of the type seen in low mass disks does not occur. A system with giant planet masses similar to our Solar System (1.0, 0.33, 0.1, 0.1 $M_{Jup}$) was stable for over 1000 yr, and a Jupiter-Saturn-like system was stable for over 3800 yr, implying that our giant planets might well survive a MGU disk phase.
    The Astrophysical Journal 01/2013; 764(2). · 6.73 Impact Factor

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Shu-ichiro Inutsuka