Physics of Tidal Disruptions

大约15年来，天体物理学家已经知道星系通常在其中心拥有超大质量黑洞（BH）。 虽然通常只能通过它们的引力来探测，但还有另一种方法可以揭示否则无法观测到的黑洞：恒星潮汐破裂，这是一颗星星碰巧非常接近这样一个黑洞时的毁灭。 为解决这一问题而开发的令人兴奋和创新的技术将得到扩展和改进，并将在许多需要数值计算的领域产生重大影响。在过去的大约十年中，已经从每一个产生的发光耀斑中发现了数十个这样的潮汐中断事件。 这种特征性的耀斑在几周到几个月的时间内逐渐衰减。 不幸的是，旧的理论在解释新的数据时遇到了困难，它的假设必须受到质疑。 最近的工作已经打开了思考这些事件的新方法，但进展受到传统数值模拟方法的极端计算需求的阻碍。 目前的团队已经建立了一个新的模拟基础设施，克服了这些障碍，并允许高质量的计算，包括完整的广义相对论和三维磁流体力学。 这一工具提供了三个新的研究途径：（1）了解黑洞吸积流和星星被撕裂后未结合碎片的喷射的性质;（2）探索黑洞旋转如何塑造吸积流并可能支持相对论喷流;以及（3）提供定量预测的光变曲线和光谱产生。社会效益来自培训一个年轻的科学家在广泛适用的大规模数值模拟技术，扩大现代教学方法在本科物理教育，并开发创新的计算方法，为未来的公开发布。

For about fifteen years, astrophysicists have known that galaxies generally house supermassive black holes (BHs) at their centers. Although usually detected only through their gravity, there is another method to reveal otherwise unobservable BHs: stellar tidal disruptions, which are the destruction of a star that happens to pass extremely close to such a BH. The exciting and innovative techniques already developed to tackle this situation will be extended and improved and will have significant impact across many fields that require numerical calculations.Over roughly the last decade, dozens of these Tidal Disruption Events have now been discovered from the luminous flare each one produces. This characteristic flare gradually decays over a span of weeks to months. Unfortunately, the old theory has trouble explaining the new data, and its assumptions must be questioned. Recent work has opened new ways of thinking about these events, but progress has been hampered by the extreme computational demands of conventional numerical simulation methods. The present team has built a new simulation infrastructure that overcomes these obstacles, and permits high-quality calculations incorporating full general relativity and three-dimensional magnetohydrodynamics. This tool enables three new avenues of research: (1) understanding the nature of both the accretion flow onto the black hole and the ejection of unbound debris after the star is torn apart; (2) exploring how black hole spin may shape the accretion flow and possibly support relativistic jets; and (3) providing quantitative predictions of the light curves and spectra produced.Societal benefits come from training a young scientist in the broadly applicable techniques of large-scale numerical simulation, expanding modern instructional methods in undergraduate physics education, and developing the innovative computing methodology for future public release.