Accretion in giant planet circumplanetary discs
Accretion in giant planet circumplanetary discs
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巨型行星环行星盘中的吸积
DOI：
10.1093/mnras/stu245
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发表时间：
2014
影响因子：
4.8
通讯作者：
M. Wardle
中科院分区：
文献类型：
--
作者：
Sarah L. Keith;M. Wardle
在巨行星的最后生长阶段，吸积被认为是由周围的环行星盘控制的。目前的天体物理吸积盘模型依赖于磁流体湍流或重力湍流作为盘内有效粘性的来源。然而，在这些模型中的磁耦合吸积区域是如此有限，磁盘可能无法支持在所有半径的流入，或在所需的速度。在这里，我们研究自洽吸积所需的条件，其中磁盘容易受到吸积驱动的磁场或引力不稳定性。我们模拟的磁盘作为一个Shakura-Sunyaev $\alpha$磁盘和计算电离的水平，磁场和磁盘之间的耦合强度使用欧姆，霍尔和Ambipolar扩散率的MRI和垂直场，和引力不稳定的强度。我们发现，标准的常数-$\alpha$磁盘仅耦合到该领域的热电离在$30\，R_J $强磁扩散性，禁止吸积通过大部分的中平面。鉴于常数-$\alpha$盘不能产生与其粘性一致的吸积，我们放弃了常数-$\alpha$的假设，并提出了一个替代模型，其中$\alpha$根据水平磁湍流或重力湍流径向变化。我们发现，垂直场可以驱动整个磁盘的吸积，而MRI可以驱动吸积到$\sim200\，R_J $，超过Toomre的$Q=1$和gravitoturbulence占主导地位。这些盘相对较热（$T\gtrsim800\，$K），因此质量较大（$M_{\text{disk}}\sim0.5\，M_J $）。
During the final growth phase of giant planets, accretion is thought to be controlled by a surrounding circumplanetary disk. Current astrophysical accretion disk models rely on hydromagnetic turbulence or gravitoturbulence as the source of effective viscosity within the disk. However, the magnetically-coupled accreting region in these models is so limited that the disk may not support inflow at all radii, or at the required rate. Here, we examine the conditions needed for self-consistent accretion, in which the disk is susceptible to accretion driven by magnetic fields or gravitational instability. We model the disk as a Shakura-Sunyaev $\alpha$ disk and calculate the level of ionisation, the strength of coupling between the field and disk using Ohmic, Hall and Ambipolar diffusevities for both an MRI and vertical field, and the strength of gravitational instability. We find that the standard constant-$\alpha$ disk is only coupled to the field by thermal ionisation within $30\,R_J$ with strong magnetic diffusivity prohibiting accretion through the bulk of the midplane. In light of the failure of the constant-$\alpha$ disk to produce accretion consistent with its viscosity we drop the assumption of constant-$\alpha$ and present an alternate model in which $\alpha$ varies radially according to the level magnetic turbulence or gravitoturbulence. We find that a vertical field may drive accretion across the entire disk, whereas MRI can drive accretion out to $\sim200\,R_J$, beyond which Toomre's $Q=1$ and gravitoturbulence dominates. The disks are relatively hot ($T\gtrsim800\,$K), and consequently massive ($M_{\text{disk}}\sim0.5\,M_J$).
DOI：
10.1111/j.1365-2966.2008.14184.x
发表时间：
2008-11
影响因子：
4.8
作者：
Ben A. Ayliffe;M. Bate
通讯作者：
Ben A. Ayliffe;M. Bate