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Star Formation Initiated by Decay of Turbulence

湍流衰变引发恒星形成

基本信息

批准号：
13640237
负责人：
HANAWA Tomoyuki
金额：
$ 2.3万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640237/
关键词：
Star Formation Turbulence Magnetohydrodynamics Self-Gravity Numerical Simulation 磁気流体波分子雲

项目摘要

Magnetohydrodynamical (MHD) waves of large amplitudes propagate in molecular clouds where star formation is now ongoing. These MHD waves are thought to prevent the molecura clouds collapsing to form stars. In other words, star formation will become active if the MHD waves decay. This idea have promoted numerical simulations which aim to derive the decay rate of the MHD waves. However, the numerical simulations so far have suffered from *erious numerical decays of the MHD waves. Also the dynamic range in the wavelength was also limited by computer resources available. We evaluated the decay due to the numerical viscosity using the analytical solution of the circularly polarized Alfven wave. We have shown that the numerical decay is small enough only when more than 32 mesh points are used to resolve a wavelength. This means that the dynamic range can be only by a factor 8 in the wavelength even when 256 mesh points are used in each spatial direction. We have also shown that the physical decay of the Alfven wave depends not only on the wavelength but on the polarization. A circularly polarized wave traveling in a filamentary cloud decays exponentially with a wavelength independent e-folding timescale. A linearly polarized one decays inversely proportional to the square of the time and the decay rate is larger for a shorter wavelength. These results were shown at two international conferences and will be shown in a refereed journal in near future.

大幅度的磁流体(MHD)波在正在形成恒星的分子云中传播。这些MHD波被认为可以防止分子云坍塌形成恒星。换句话说，如果MHD波衰变，恒星形成将变得活跃。这一想法促进了旨在推导MHD波衰减率的数值模拟。然而，到目前为止，数值模拟一直受到*强烈的MHD波的数值衰减的影响。此外，波长的动态范围也受到可用计算机资源的限制。我们利用圆极化Alfven波的解析解估计了由于数值粘性引起的衰变。我们已经证明，只有当使用超过32个网格点来解析一个波长时，数值衰减才足够小。这意味着，即使在每个空间方向上使用256个网格点，动态范围也只能是波长的8倍。我们还证明了阿尔芬波的物理衰减不仅与波长有关，而且与偏振有关。在丝状云团中传播的圆偏振波以与波长无关的e折叠时间尺度指数衰减。线偏振光的衰减率与时间的平方成反比，波长越短，衰减率越大。这些结果已在两次国际会议上展示，并将在不久的将来发表在一份经评审的期刊上。