Observational Study of the Role of Magnetic Fields in Star Formation

为了理解恒星的形成和磁场在星际云的形成和演化中的作用，理论上的努力是广泛的，而且正在加速。然而，尽管近年来取得了重大进展，关于恒星形成的基本物理问题仍然没有得到解答。如果致密的分子云的寿命比自由落体崩塌时间长得多，那么它们就必须受到支撑，以抵御引力崩塌。一种观点认为，磁场提供了这种支持。这一假设可以通过测量稠密云中的质量与磁通量之比来验证。另一个极端是磁场很弱，分子云是间歇性现象，云的长时间支持问题无关紧要。该项目将直接或间接测量具有统计意义的大样本分子云的磁场强度，以帮助回答上述问题。由于所需的测量是来自分子云的弱极化连续谱和谱线发射，星际磁场的测量仍然是最困难的天文观测之一，关于磁场的信息仍然非常稀少。星际磁场的测量继续取得进展，这对我们理解恒星形成的基本物理过程至关重要。

AST-0205810PI CrutcherThe theoretical effort to understand star formation and the role of magnetic fields in the formation and evolution of interstellar clouds is extensive and accelerating. However, in spite of significant progress in recent years, there remain fundamental unanswered questions about the basic physics of star formation. If dense molecular clouds have lifetimes significantly longer than their free-fall collapse times, they must be supported against gravitational collapse. One view is that magnetic fields provide this support. This hypothesis can be tested by measurement of the mass to magnetic flux ratio in dense clouds. The other extreme is that magnetic fields are weak and that molecular clouds are intermittent phenomena, and that the problem of cloud support for long time periods is irrelevant. This project will measure, directly or indirectly, magnetic field strengths in a large, statistically meaningful sample of molecular clouds in order to help answer the above questions. Because the requisite measurements are of weakly polarized continuum and spectral-line emission from molecular clouds, measurements of interstellar magnetic fields remain among the most difficult of astronomical observations, and information about magnetic fields remains very sparse. It is crucial to our understanding of the fundamental physical process of star formation that measurements of interstellar magnetic fields continue to progress.***