分子云中恒星形成细丝的形成与演化

English | 2024 | ASIN: B0DBBD2C2R | 168 pages| Epub PDF (True) | 38 MB

This book clears up some confusion in the field of star formation and proposes a solution to a problem that remains unsolved for more than a decade. Observations of molecular clouds show that dense filaments are the sites of present-day star formation, and it is thus necessary to understand the filament formation process because the filament is an initial condition in a star formation process. Theoretical studies suggest that shock waves in molecular clouds trigger filament formation. Several different mechanisms have been proposed, and the formation mechanism of the observed star-forming filaments is expected to be clarified. In this book, the author performs a series of isothermal magnetohydrodynamics (MHD) simulations of filament formation and identifies the formation mechanisms. It is found that the dominant filament formation mode changes with the velocity of the shock waves that trigger the filament formation. The filament width plays an important role in determining the fragmentation scale by self-gravity, and observations show that the width 0.1 pc is universal. On the other hand, in theory the width of the supercritical filaments was considered to be narrowed by self-gravity. Recent studies suggest that massive filaments are bound by the slow shocks that are caused by accretion flows onto the filaments. Since the wavefront of such a slow shock is known to be unstable as a slow shock instability (SSI), the accretion ram pressure is expected to be converted into thermal/turbulent pressure across the shock front, which potentially maintains the width. In the scale of dense filaments, ambipolar diffusion (AD) suppresses the SSI at small scales. The influence of AD on SSI is investigated using two-dimensional MHD simulations, and the nonlinear evolution of the SSI with AD is found to drive turbulences. The book demonstrate the effect of SSI including AD onto the filament evolution.

中文|2024|ASIN:B0DBBD2C2R|168页|Epub PDF（True）|38 MB这本书澄清了恒星形成领域的一些困惑，并提出了一个十多年来仍未解决的问题的解决方案。对分子云的观测表明，密集的细丝是当今恒星形成的场所，因此有必要了解细丝形成过程，因为细丝是恒星形成过程中的初始条件。理论研究表明，分子云中的冲击波会触发细丝的形成。已经提出了几种不同的机制，预计观测到的恒星形成细丝的形成机制将得到澄清。在这本书中，作者对细丝形成进行了一系列等温磁流体动力学（MHD）模拟，并确定了形成机制。研究发现，主导的细丝形成模式随着触发细丝形成的冲击波的速度而变化。细丝宽度在确定自重破碎规模方面起着重要作用，观测表明，0.1pc的宽度是普遍适用的。另一方面，理论上认为超临界长丝的宽度会因自重而变窄。最近的研究表明，巨大的细丝受到细丝上吸积流引起的缓慢冲击的束缚。由于已知这种慢激波的波阵面是不稳定的，即慢激波不稳定性（SSI），因此预计吸积闸板压力将转化为激波前沿的热/湍流压力，这可能会保持宽度。在致密细丝的尺度上，双极扩散（AD）在小尺度上抑制SSI。使用二维MHD模拟研究了AD对SSI的影响，发现SSI随AD的非线性演化会驱动湍流。该书展示了包括AD在内的SSI对长丝演变的影响。

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