From Planetesimal to Planet in Turbulent Disks. II. Formation of Gas Giant Planets

Hiroshi Kobayashi1 and Hidekazu Tanaka2
The Astrophysical Journal 862, 127 Link to Article [https://doi.org/10.3847/1538-4357/aacdf5]
1Department of Physics, Nagoya University, Nagoya, Aichi 464-8602, Japan
2Astronomical Institute, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan

In the core accretion scenario, gas giant planets are formed form solid cores with several Earth masses via gas accretion. We investigate the formation of such cores via collisional growth from kilometer-sized planetesimals in turbulent disks. The stirring by forming cores induces collisional fragmentation, and surrounding planetesimals are ground down until radial drift. The core growth is therefore stalled by the depletion of surrounding planetesimals due to collisional fragmentation and radial drift. The collisional strength of planetesimals determines the planetesimal-depletion timescale, which is prolonged for large planetesimals. The size of planetesimals around growing cores is determined by the planetesimal size distribution at the onset of runaway growth. Strong turbulence delays the onset of runaway growth, resulting in large planetesimals. Therefore, the core mass evolution depends on the turbulent parameter α; the formation of cores massive enough without significant depletion of surrounding planetesimals needs a strong turbulence of α gsim 10−3. However, strong turbulence with α gsim 10−3 leads to a significant delay of the onset of runaway growth and prevents the formation of massive cores within the disk lifetime. The formation of cores massive enough within several million years therefore requires that solid surface densities are several times higher, which is achieved in the inner disk lesssim10 au due to pile-up of drifting dust aggregates. In addition, the collisional strength ${Q}_{{\rm{D}}}^{* }$ even for kilometer-sized or smaller bodies affects the growth of cores; ${Q}_{{\rm{D}}}^{* }\gtrsim {10}^{7}\,\mathrm{erg}\,{{\rm{g}}}^{-1}$ for bodies lesssim1 km is likely for this gas giant formation.

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