arXiv subjects

Yota Ishigaki

Publications and source records attributed to Yota Ishigaki.

3 recordsLinked to original sources

arXiv2023

$N$-body simulation of planetary formation through pebble accretion in a radially structured protoplanetary disk

In the conventional theory of planet formation, it is assumed that protoplanetary disks are axisymmetric and have a smooth radial profile. However, recent radio observations of protoplanetary disks have revealed that many of them have complex radial structures. In this study, we perform a series of $N$-body simulations to investigate how planets are formed in protoplanetary disks with radial structures. For this purpose, we consider the effect of continuous pebble accretion onto the discontinuity boundary within the terrestrial planet-forming region ($\sim0.6$ AU). We found that protoplanets grow efficiently at the discontinuity boundary, reaching the Earth mass within $\sim10^4$ years. We confirmed that giant collisions of protoplanets occur universally in our model. Moreover, we found that multiple planet-sized bodies form at regular intervals in the vicinity of the discontinuity boundary. These results indicate the possibility of the formation of solar system-like planetary systems in radially structured protoplanetary disks.

astro-ph.EP↗

arXiv2021

Particle-particle Particle-tree Code for Planetary System Formation with Individual Cut-off Method: GPLUM

In a standard theory of the formation of the planets in our Solar System, terrestrial planets and cores of gas giants are formed through accretion of kilometer-sized objects (planetesimals) in a protoplanetary disk. Gravitational $N$-body simulations of a disk system made up of numerous planetesimals are the most direct way to study the accretion process. However, the use of $N$-body simulations has been limited to idealized models (e.g. perfect accretion) and/or narrow spatial ranges in the radial direction, due to the limited number of simulation runs and particles available. We have developed new $N$-body simulation code equipped with a particle-particle particle-tree (${\rm P^3T}$) scheme for studying the planetary system formation process: GPLUM. For each particle, GPLUM uses the fourth-order Hermite scheme to calculate gravitational interactions with particles within cut-off radii and the Barnes-Hut tree scheme for particles outside the cut-off radii. In existing implementations, ${\rm P^3T}$ schemes use the same cut-off radius for all particles, making a simulation become slower when the mass range of the planetesimal population becomes wider. We have solved this problem by allowing each particle to have an appropriate cut-off radius depending on its mass, its distance from the central star, and the local velocity dispersion of planetesimals. In addition to achieving a significant speed-up, we have also improved the scalability of the code to reach a good strong-scaling performance up to 1024 cores in the case of $N=10^6$. GPLUM is freely available from https://github.com/YotaIshigaki/GPLUM with MIT license.

astro-ph.EP↗

arXiv2020

Orbital evolution of Saturn's satellites due to the interaction between the moons and massive Saturn's rings

Saturn's mid-sized moons (satellites) have a puzzling orbital configuration with trapping in mean-motion resonances with every other pairs (Mimas-Tethys 4:2 and Enceladus-Dione 2:1). To reproduce their current orbital configuration on the basis of Crida & Charnoz's model of satellite formation from a hypothetical ancient massive rings, adjacent pairs must pass 1st-order mean-motion resonances without being trapped. The trapping could be avoided by fast orbital migration and/or excitation of the satellite's eccentricity caused by gravitational interactions between the satellites and the rings (the disk), which are still unknown. In our research, we investigate the satellite orbital evolution due to interactions with the disk through full N-body simulations. We performed global high-resolution N-body simulations of a self-gravitating particle disk interacting with a single satellite. We used $N \sim 10^5$ particles for the disk. Gravitational forces of all the particles and their inelastic collisions are taken into account. As a result, dense short-wavelength wake structure is created by the disk self-gravity and global spiral arms with $m \sim$ a few is induced by the satellite. The self-gravity wakes regulate the orbital evolution of the satellite, which has been considered as a disk spreading mechanism but not as a driver for the orbital evolution. The self-gravity wake torque to the satellite is so effective that the satellite migration is much faster than that was predicted with the spiral arms torque. It provides a possible model to avoid the resonance capture of adjacent satellite pairs and establish the current orbital configuration of Saturn's mid-sized satellites.

astro-ph.EP↗