The Final Hour of a Massive Star: Silicon Shell Burning and the Subsequent Supernova

大质量恒星（大于太阳质量的9倍）生命的最后阶段是硅（SiSB）的核聚变（“燃烧”），在惰性铁核周围的外壳中产生铁，增加铁核的质量。这个阶段可以持续长达一个小时，直到铁核的增长触发它坍缩成一个紧凑而致密的中子星（NS），被吸积物质包围。被称为中微子的亚原子粒子由新NS发射出来，加热这些物质，并以激波的形式将它们赶出周围的恒星，产生超新星爆炸，将新形成的元素传递到星系的星际介质中。田纳西大学诺克斯维尔分校的一个研究小组将使用最先进的计算模拟代码，对大质量恒星的SiSB阶段进行多维计算机模拟，通过崩溃/超新星阶段，以更好地理解原子元素产生和分散的关键过程。PI将举办关于超新星科学和核合成或元素创造的公开讲座，并在恒星天体物理学和大规模计算方面培养一名研究生。研究组将模拟大质量恒星内部对流硅壳燃烧的最后一个小时的发展过程，并继续模拟到超新星爆炸阶段。该团队将运行具有现实微物理学的多维代码，包括核合成、中微子传输和湍流对流。由于代码在三维空间中运行，他们将能够引入不对称性，这是非常重要的，特别是对于超新星中微子加热机制。预坍缩燃烧模型将探索充分捕捉这一动态恒星阶段所需的维数、空间分辨率、核网络完整性和持续时间的限制。爆炸模拟将计算超新星产生的元素以及中微子和引力波信号。提议的工作将使用一种名为Chimera的模拟代码，PI将其描述为三个独立的成熟代码的组合，涵盖了问题的三个方面。

The final stage of life for a massive star (larger than about nine times the mass of the Sun) is the nuclear fusion ("burning") of silicon (SiSB) to create iron in a shell around an inert iron core, increasing the mass of the iron core.  This stage can last up to an hour until growth of the iron core triggers its collapse to a compact and dense neutron star (NS) surrounded by accreting material. Subatomic particles called neutrinos emitted by the new NS heat the material and drive it out in a shock front through the surrounding star, generating a supernova explosion that delivers newly made elements into the interstellar medium of the galaxy. A research team at the University of Tennessee, Knoxville, will follow multidimensional computer simulations of the SiSB phase through the collapse/supernova phase in massive stars using state-of-the-art computational simulation codes to better understand this critical process for creating and dispersing atomic elements. The PI will present public lectures on supernova science and nucleosynthesis, or element creation, and train a graduate student in both stellar astrophysics and large-scale computation.The research team will simulate the developments in the last hour of convective silicon shell burning in a massive star and continue the simulations into the supernova explosion phase. The team will run a multi-dimensional code with realistic microphysics, including nucleosynthesis, neutrino transport, and turbulent convection. Since the code runs in three dimensions, they will be able to introduce asymmetries, which are known to be important, particularly for the supernova neutrino heating mechanism. The pre-collapse burning models will explore the limits of dimensionality, spatial resolution, nuclear network completeness, and duration required to adequately capture this dynamic stellar phase. The explosion simulations will calculate the element production from the supernova along with neutrino and gravitational wave signals. The proposed work will use a simulation code called Chimera, which the PI describes as a combination of three separate mature codes covering three aspects of the problem.