Centrifugal barrier and super-Keplerian rotation in protostellar disc formation
Centrifugal barrier and super-Keplerian rotation in protostellar disc formation
复制标题
原星盘形成中的离心势垒和超开普勒旋转
DOI：
10.1093/mnras/stac1842
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发表时间：
2022
影响因子：
4.8
通讯作者：
Tu, Yisheng
中科院分区：
文献类型：
--
作者：
Jones, Dylan C.;Lam, Ka Ho;Li, Zhi-Yun;Tu, Yisheng
随着ALMA的出现，现在有可能从观测上限制深埋在原恒星周围的圆盘的形成方式。特别值得一提的是，最近对附近原恒星L1527的ALMA C3H2线观测被解释为所谓的“离心障”的证据，即原恒星包层在超开普勒式自转区域的离心力的作用下逐渐减速至停止。为了测试离心势垒的概念，它最初是基于旋转的测试粒子围绕固定点质量的角动量守恒-坍塌，我们对原恒星盘的形成进行了简单的轴对称流体动力学模拟，包括最小一组成分：自重、旋转和使盘能够共生的规定粘度。我们发现，当粘性相对较大时，确实可以存在超开普勒区，但与离心势垒的经典图景不同，流入的包络材料不是仅仅受到离心力的减速。该区域比其周围的包层物质具有更具体的角动量，这表明盘中向外角动量传输的起源(受流入包层的盘膨胀的约束)，而不是经典图像中所设想的包层物质的自旋，因为它更接近中心以保持角动量。对于较小的粘性，超开普勒式转动较弱或不存在。我们的结论是，尽管在某些参数区域内存在超开普勒式旋转，但我们的模拟并不支持离心势垒的经典图景。
With the advent of ALMA, it is now possible to observationally constrain how discs form around deeply embedded protostars. In particular, the recent ALMA C3H2line observations of the nearby protostar L1527 have been interpreted as evidence for the so-called ‘centrifugal barrier,’ where the protostellar envelope infall is gradually decelerated to a stop by the centrifugal force in a region of super-Keplerian rotation. To test the concept of centrifugal barrier, which was originally based on angular momentum conserving-collapse of a rotating test particle around a fixed point mass, we carry out simple axisymmetric hydrodynamic simulations of protostellar disc formation including a minimum set of ingredients: self-gravity, rotation, and a prescribed viscosity that enables the disc to accrete. We find that a super-Keplerian region can indeed exist when the viscosity is relatively large but, unlike the classic picture of centrifugal barrier, the infalling envelope material is not decelerated solely by the centrifugal force. The region has more specific angular momentum than its surrounding envelope material, which points to an origin in outward angular momentum transport in the disc (subject to the constraint of disc expansion by the infalling envelope), rather than the spin-up of the envelope material envisioned in the classic picture as it falls closer to the centre in order to conserve angular momentum. For smaller viscosities, the super-Keplerian rotation is weaker or non-existing. We conclude that, despite the existence of super-Keplerian rotation in some parameter regime, the classic picture of centrifugal barrier is not supported by our simulations.