星周盘二维数值模拟中死区边界的行星形成爆发
Planet formation bursts at the borders of the dead zone in 2D numerical simulations of circumstellar disks
摘要：
由于原行星盘中的吸积是由湍流粘性实现的，因此活动区和非活动区（死区）之间的边界构成了吸积流发生突变的位置。气体的积聚引发了罗斯贝波的不稳定性，而罗斯贝波的不稳定性又反过来饱和成反气旋涡旋。有人认为，固体被困在其中导致了行星形成的爆发在非常短的时间尺度。本文用二维非磁化薄原行星盘中气体和固体的动力学进行了全球模拟。我们使用半径为1，10，30和100厘米的多个粒子种类，通过粒子网格方法求解粒子的引力相互作用。死区被建模为低粘度区域。绝热和局部等温状态方程。我们发现，Rossby波不稳定性是在各种条件下触发，从而使涡旋形成一个强大的过程。在漩涡内部，固体物质会快速积聚，粒子会在短至五个轨道的时间内坍缩成行星质量的物体。由于拖曳力是大小相关的，空气动力学分选包围在旋涡运动中，并且形成的第一束缚结构主要由类似大小的颗粒组成。除了由于冲压压力的侵蚀，我们确定气体潮汐从大规模的旋涡作为一个破坏剂形成的原行星胚胎。我们还估计了模拟结束时组成最大胚胎的粒子的碰撞速度历史，发现其中绝大多数从未经历过与速度超过1 m/s的另一个粒子的碰撞。
英文摘要：
As accretion in protoplanetary disks is enabled by turbulent viscosity, the border between active and inactive (dead) zones constitutes a location where there is an abrupt change in the accretion flow. The gas accumulation that ensues triggers the Rossby wave instability, that in turn saturates into anticyclonic vortices. It was suggested that the trapping of solids within them leads to a burst of planet formation on very short timescales. We perform two-dimensional global simulations of the dynamics of gas and solids in a non-magnetized thin protoplanetary disk with the Pencil Code. We use multiple particle species of radius 1, 10, 30, and 100 cm, solving for the particles' gravitational interaction by a particle-mesh method. The dead zone is modeled as a region of low viscosity. Adiabatic and locally isothermal equations of state are used. We find that the Rossby wave instability is triggered under a variety of conditions, thus making vortex formation a robust process. Inside the vortices, fast accumulation of solids occurs and the particles collapse into objects of planetary mass in timescales as short as five orbits. Because the drag force is size-dependent, aerodynamical sorting ensues within the vortical motion, and the first bound structures formed are composed primarily of similarly-sized particles. In addition to erosion due to ram pressure, we identify gas tides from the massive vortices as a disrupting agent of formed protoplanetary embryos. We also estimate the collisional velocity history of the particles that compose the most massive embryo by the end of the simulation, finding that the vast majority of them never experienced a collision with another particle at speeds faster than 1 m/s.
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