Circumplanetary Disk Formation (original) (raw)
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Circum-planetary discs as bottlenecks for gas accretion onto giant planets
Astronomy & Astrophysics, 2012
Context. With hundreds of exoplanets detected, it is necessary to revisit giant planets accretion models to explain their mass distribution. In particular, formation of sub-jovian planets remains unclear, given the short timescale for the runaway accretion of massive atmospheres. However, gas needs to pass through a circum-planetary disc. If the latter has a low viscosity (as expected if planets form in "dead zones"), it might act as a bottleneck for gas accretion. Aims. We investigate what the minimum accretion rate is for a planet under the limit assumption that the circumplanetary disc is totally inviscid, and the transport of angular momentum occurs solely because of the gravitational perturbations from the star. Methods. To estimate the accretion rate, we present a steady-state model of an inviscid circum-planetary disc, with vertical gas inflow and external torque from the star. Hydrodynamical simulations of a circum-planetary disc were conducted in 2D, in a planetocentric frame, with the star as an external perturber in order to measure the torque exerted by the star on the disc. Results. The disc shows a two-armed spiral wave caused by stellar tides, propagating all the way in from the outer edge of the disc towards the planet. The stellar torque is small and corresponds to a doubling time for a Jupiter mass planet of the order of 5 Myrs. Given the limit assumptions, this is clearly a lower bound of the real accretion rate.
CAPTURE AND EVOLUTION OF PLANETESIMALS IN CIRCUMJOVIAN DISKS
We study the evolution of planetesimals in evolved gaseous disks that orbit a solar-mass star and harbor a Jupitermass planet at a 5 p ≈ AU. The gas dynamics are modeled with a three-dimensional hydrodynamics code that employs nested grids and achieves a resolution of one Jupiter radius in the circumplanetary disk. The code models solids as individual particles. Planetesimals are subjected to gravitational forces by the star and the planet, a drag force by the gas, disruption via ram pressure, and mass loss through ablation. The mass evolution of solids is calculated self-consistently with their temperature, velocity, and position. We consider icy and icy/rocky bodies of radius 0.1-100 km, initially deployed on orbits around the star within a few Hill radii (R H) of the planetʼs orbit. Planetesimals are scattered inward, outward, and toward disk regions of radius r a p ≫. Scattering can relocate significant amounts of solids, provided that regions r a 3 p | − | ∼ R H are replenished with planetesimals. Scattered bodies can be temporarily captured on planetocentric orbits. Ablation consumes nearly all solids at gas temperatures 220 ≳ K. Super-Keplerian rotation around and beyond the outer edge of the gas gap can segregate 0.1 km ≲ bodies, producing solid gap edges at size-dependent radial locations. Capture, break-up, and ablation of solids result in a dust-laden circumplanetary disk with low surface densities of kilometer sized planetesimals, implying relatively long timescales for satellite formation. After a giant planet acquires most of its mass, accretion of solids is unlikely to significantly alter its heavy element content. The luminosity generated by accretion of solids and the contraction luminosity can be of similar orders of magnitude.
Angular Momentum Accretion onto a Gas Giant Planet
The Astrophysical Journal, 2008
We investigate the accretion of angular momentum onto a protoplanet system using three-dimensional hydrodynamical simulations. We consider a local region around a protoplanet in a protoplanetary disk with sufficient spatial resolution. We describe the structure of the gas flow onto and around the protoplanet in detail. We find that the gas flows onto the protoplanet system in the vertical direction crossing the shock front near the Hill radius of the protoplanet, which is qualitatively different from the picture established by two-dimensional simulations. The specific angular momentum of the gas accreted by the protoplanet system increases with the protoplanet mass. At Jovian orbit, when the protoplanet mass M p is M p 1M J , where M J is Jovian mass, the specific angular momentum increases as j ∝ M p . On the other hand, it increases as j ∝ M 2/3 p when the protoplanet mass is M p 1M J . The stronger dependence of the specific angular momentum on the protoplanet mass for M p 1M J is due to thermal pressure of the gas. The estimated total angular momentum of a system of a gas giant planet and a circumplanetary disk is two-orders of magnitude larger than those of the present gas giant planets in the solar system. A large fraction of the total angular momentum contributes to the formation of the circumplanetary disk. We also discuss the satellite formation from the circumplanetary disk.
Evolution of Giant Planets in Eccentric Disks
Astrophysical Journal, 2006
We investigate the interaction between a giant planet and a viscous circumstellar disk by means of high-resolution, two-dimensional hydrodynamical simulations. We consider planet masses that range from 1 to 3 Jupiter masses (M J ) and initial orbital eccentricities that range from 0 to 0.4. We find that a planet can cause eccentricity growth in a disk region adjacent to the planet's orbit, even if the planet's orbit is circular. Disk-planet interactions lead to growth in a planet's orbital eccentricity. The orbital eccentricities of a 2 M J and a 3 M J planet increase from 0 to 0.11 within about 3000 orbits. Over a similar time period, the orbital eccentricity of a 1 M J planet grows from 0 to 0.02. For a case of a 1 M J planet with an initial eccentricity of 0.01, the orbital eccentricity grows to 0.09 over 4000 orbits. Radial migration is directed inwards, but slows considerably as a planet's orbit becomes eccentric. If a planet's orbital eccentricity becomes sufficiently large, e 0.2, migration can reverse and so be directed outwards. The accretion rate towards a planet depends on both the disk and the planet orbital eccentricity and is pulsed over the orbital period. Planet mass growth rates increase with planet orbital eccentricity. For e ∼ 0.2 the mass growth rate of a planet increases by ∼ 30% above the value for e = 0. For e 0.1, most of the accretion within the planet's Roche lobe occurs when the planet is near the apocenter. Similar accretion modulation occurs for flow at the inner disk boundary which represents accretion toward the star.
Planet formation models: the interplay with the planetesimal disc
Astronomy & Astrophysics, 2012
Context. According to the sequential accretion model (or core-nucleated accretion model), giant planet formation is based first on the formation of a solid core which, when massive enough, can gravitationally bind gas from the nebula to form the envelope. The most critical part of the model is the formation time of the core: to trigger the accretion of gas, the core has to grow up to several Earth masses before the gas component of the protoplanetary disc dissipates. Aims. We calculate planetary formation models including a detailed description of the dynamics of the planetesimal disc, taking into account both gas drag and excitation of forming planets. Methods. We computed the formation of planets, considering the oligarchic regime for the growth of the solid core. Embryos growing in the disc stir their neighbour planetesimals, exciting their relative velocities, which makes accretion more difficult. Here we introduce a more realistic treatment for the evolution of planetesimals' relative velocities, which directly impact on the formation timescale. For this, we computed the excitation state of planetesimals, as a result of stirring by forming planets, and gas-solid interactions. Results. We find that the formation of giant planets is favoured by the accretion of small planetesimals, as their random velocities are more easily damped by the gas drag of the nebula. Moreover, the capture radius of a protoplanet with a (tiny) envelope is also larger for small planetesimals. However, planets migrate as a result of disc-planet angular momentum exchange, with important consequences for their survival: due to the slow growth of a protoplanet in the oligarchic regime, rapid inward type I migration has important implications on intermediate-mass planets that have not yet started their runaway accretion phase of gas. Most of these planets are lost in the central star. Surviving planets have masses either below 10 M ⊕ or above several Jupiter masses. Conclusions. To form giant planets before the dissipation of the disc, small planetesimals (∼0.1 km) have to be the major contributors of the solid accretion process. However, the combination of oligarchic growth and fast inward migration leads to the absence of intermediate-mass planets. Other processes must therefore be at work to explain the population of extrasolar planets that are presently known.
Thermohydrodynamics of Circumstellar Disks with High-Mass Planets
Astrophysical Journal, 2003
With a series of numerical simulations, we analyze the thermohydrodynamic evolution of circumstellar disks containing Jupiter-sized protoplanets. In the framework of a two-dimensional approximation, we consider an energy equation that includes viscous heating and radiative effects in a simplified yet consistent form. Multiple nested grids are used in order to study both global and local features around the planet. By means of different viscosity prescriptions, we investigate various temperature regimes. A planetary mass range from 0.1 to 1 MJ is examined. Computations show that gap formation is a general property that affects density, pressure, temperature, optical thickness, and radiated flux distributions. However, it remains a prominent feature only when the kinematic viscosity is on the order of 1015cm2s-1 or lower, although it becomes rather shallow for 0.1 MJ perturbers. Around accreting planets, a circumplanetary disk forms that has a surface density profile decaying exponentially with distance and whose mass is 5-6 orders of magnitude smaller than Jupiter's mass. Circumplanetary disk temperature profiles decline roughly as the inverse of the distance from the planet, matching the values measured in the gap toward the border of the Roche lobe. Temperatures range from some 10 to ~1000 K. Moreover, circumplanetary disks are generally opaque, with optical thicknesses larger than 1 and aspect ratios around a few tenths. Nonaccreting protoplanets provide quite different scenarios, with a clockwise, i.e., reversed flow, rotation around low-mass bodies. Planetary accretion and migration rates depend on the viscosity regime, with discrepancies within an order of magnitude. Co-orbital torques increase as viscosity increases. For high viscosities, type I migration may extend to larger planetary masses. Estimates of growth and migration timescales inferred from these models are on the same orders of magnitude as those previously obtained with locally isothermal simulations, in both two and three dimensions.
Monthly Notices of the Royal Astronomical Society, 2013
We report the results of our three-dimensional radiation hydrodynamics simulation of collapsing unmagnetized molecular cloud cores. We investigate the formation and evolution of the circumstellar disk and the clumps formed by disk fragmentation. Our simulation shows that disk fragmentation occurs in the early phase of circumstellar disk evolution and many clumps form. The clump can be represented by a polytrope sphere of index n ∼ 3 and n 4 at central temperature T c 100 K and T c 100 K, respectively. We demonstrate, numerically and theoretically, that the maximum mass of the clump, beyond which it inevitably collapses, is ∼ 0.03 M ⊙ . The entropy of the clump increases during its evolution, implying that evolution is chiefly determined by mass accretion from the disk rather than by radiative cooling. Although most of the clumps rapidly migrate inward and finally fall onto the protostar, a few clumps remain in the disk. The central density and temperature of the surviving clump rapidly increase and the clump undergoes a second collapse within 1000 -2000 years after its formation. In our simulation, three second cores of masses 0.2 M ⊙ , 0.15 M ⊙ , and 0.06 M ⊙ formed. These are protostars or brown dwarfs rather than protoplanets. For the clumps to survive as planetary-mass objects, the rapid mass accretion should be prevented by some mechanisms.
The Astrophysical Journal, 2009
We study rapidly accreting, gravitationally unstable disks with a series of global, three dimensional, numerical experiments using the code ORION. In this paper we conduct a numerical parameter study focused on protostellar disks, and show that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the disk's accretion rate to its sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infall rate, and governed by gravitational torques generated by low-m spiral modes. We also confirm the existence of a maximum stable disk mass: disks that exceed ∼ 50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.
Exploring the architectures of planetary systems that form in thermally evolving viscous disc models
2016
The diversity in observed planets and planetary systems has raised the question of whether they can be explained by a single model of planet formation or whether multiple models are required. The work presented in this thesis aims to examine the oligarchic growth scenario, to determine whether the core accretion model, where planets form bottom-up, can recreate the observed diversity. I begin by exploring how changing model parameters such as disc mass and metallicity influence the types of planetary systems that emerge. I show that rapid inward migration leads to very few planets with masses mp > 10M⊕ surviving, with surviving planetary systems typically containing numerous low-mass planets. I examine what conditions are required for giant planets to form and survive migration, finding that for a planet similar to Jupiter to form and survive, it must form at an orbital radius rp > 10 au. In the second project in this thesis, I update the physical models before examining wheth...
2010
The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing clouds, the first (adiabatic) core with a size of ~10AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure, and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually, and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk. This indicates that the circumstellar disk is formed before the protostar formation with a size of ~10AU, which means that no protoplanetary disk smaller than <10AU exists. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the circumstellar disk has a mass of ~0.01-0.1 solar mass, while the protostar has a mass of ~...