原始原恒星系统的形成和演化
Formation and evolution of primordial protostellar systems
摘要：
我们调查形成的第一颗恒星在宇宙黑暗时代结束时，一套三维的，移动网格模拟，直接解决崩溃的气体超出形成的第一颗原恒星在中心的暗物质minihalo。模拟涵盖了超过25个数量级的密度，并有一个最大的空间分辨率为0.05 R_sun，这远远低于个别原恒星的半径，并捕捉它们与周围气体的相互作用。在类比以前的研究中，采用下沉粒子，我们发现，开普勒光盘周围的初级原恒星碎片成一些次级原恒星，这是促进H2碰撞解离冷却和碰撞诱导发射。原恒星系统的进一步演化的特征是强大的引力矩，在圆盘中形成的次级原恒星和周围气体之间传递角动量。这导致大约一半的次级原恒星在自由落体时间内迁移到云的中心，在那里它们与初级原恒星合并，并将其质量提高到第二大原恒星质量的五倍左右。同样，一小部分原恒星通过N体相互作用从其他原恒星获得角动量，并迁移到更高的轨道。平均而言，只有三分之一的原恒星存活到模拟结束。然而，在任何给定时间存在的原恒星的数量单调增加，这表明系统将继续增长超过这里模拟的有限时间段。
英文摘要：
We investigate the formation of the first stars at the end of the cosmic dark ages with a suite of three-dimensional, moving mesh simulations that directly resolve the collapse of the gas beyond the formation of the first protostar at the centre of a dark matter minihalo. The simulations cover more than 25 orders of magnitude in density and have a maximum spatial resolution of 0.05 R_sun, which extends well below the radius of individual protostars and captures their interaction with the surrounding gas. In analogy to previous studies that employed sink particles, we find that the Keplerian disc around the primary protostar fragments into a number of secondary protostars, which is facilitated by H2 collisional dissociation cooling and collision-induced emission. The further evolution of the protostellar system is characterized by strong gravitational torques that transfer angular momentum between the secondary protostars formed in the disc and the surrounding gas. This leads to the migration of about half of the secondary protostars to the centre of the cloud in a free-fall time, where they merge with the primary protostar and enhance its growth to about five times the mass of the second most massive protostar. By the same token, a fraction of the protostars obtain angular momentum from other protostars via N-body interactions and migrate to higher orbits. On average, only every third protostar survives until the end of the simulation. However, the number of protostars present at any given time increases monotonically, suggesting that the system will continue to grow beyond the limited period of time simulated here.
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