Astrophysical transients and compact objects

这项研究计划旨在了解与恒星质量致密物体相关的宇宙爆炸的物理学。最初的焦点是中子星合并和核心塌缩超新星。这些爆炸是在地球上的实验室无法实现的极端条件下进行的，因此与物理学的前沿问题有关，例如超核密度下物质的性质、重元素的起源、引力的性质和中微子的性质。该计划的长期目标是通过科学计算提高我们对这类宇宙爆炸的理论理解，从而有助于更可靠的观测预测和检验物理理论。考虑到所涉及的过程的复杂性，需要使用数值方法。经过高性能计算和高级分析技术培训的高素质人员将是该计划的许多有益成果之一。*中子星合并很可能在2017-2021年期间由Advanced LIGO/Virgo在引力波中探测到。电磁发射的并行检测将显著减少引力波信号中的不确定性，并提供丰富的附加信息。该计划的第一个短期目标是改善对这些事件产生的最容易检测到的电磁信号的预测：由r过程元素的放射性衰变提供动力的类似超新星的瞬变(所谓的千诺瓦)。为此，将对合并残余物进行多维、多物理、随时间变化的模拟。这些模拟将系统地解决当前建模中的不确定性，从而改善全球观测界的观测和核合成预测。尽管在观测上这些超新星与大质量恒星的死亡之间存在着确凿的联系，但核心坍塌超新星的爆炸机制仍然是一个悬而未决的理论问题。这些爆炸用重元素丰富了宇宙，是中子星和恒星质量黑洞的诞生地。现有证据表明，爆炸机制本质上是不对称的。该计划的第二个短期目标是研究破坏球对称的流体动力不稳定性的影响：站立吸积激波不稳定性(SASI)和中微子驱动的对流。将进行不同复杂程度的多维模拟，以阐明在新制度下这些不稳定性的物理原因以及由此产生的观测后果。这一结果将对预期来自下一颗银河系核心坍塌超新星的中微子和引力波信号产生影响，并将揭示相关的天体物理问题，如脉冲星诞生时的自转和踢球的分布。

This research program aims to understand the physics of cosmic explosions related to stellar-mass compact objects. The initial focus is on neutron star mergers and core-collapse supernovae. These explosions operate under extreme conditions not achievable in laboratories on Earth, and thereby connect to frontier questions in physics such as the properties of matter at supra-nuclear densities, the origin of heavy elements, the nature of gravity, and the properties of neutrinos. The long-term goal of the program is to improve our theoretical understanding of this class of cosmic explosions through scientific computing, thereby contributing to more reliable observational predictions and to test physical theories. Numerical methods are required given the complexity of the processes involved. Highly-qualified personnel trained in high-performance computing and advanced analysis techniques will be one of the many beneficial results of this program.******Neutron star mergers are likely to be detected in gravitational waves in the period 2017-2021 by Advanced LIGO/Virgo. Concurrent detection of electromagnetic emission will significantly decrease uncertainties in the gravitational wave signal and provide a wealth of additional information. The first short-term goal of the program is to improve predictions for the most easily detectable electromagnetic signal generated by these events: a supernova-like transient powered by the radioactive decay of r-process elements (a so-called kilonova). To this end, multi-dimensional, multi-physics, time-dependent simulations of the merger remnant will be conducted. These simulations will systematically address current uncertainties in modeling, thus improving observational and nucleosynthetic predictions for the global observational community.******The explosion mechanism of core-collapse supernovae remains an unsolved theoretical problem, despite a firm observational association between these supernovae and the death of massive stars. These explosions enrich the Universe with heavy elements, and are the birth sites of neutron stars and stellar-mass black holes. Existing evidence suggests that the explosion mechanism is intrinsically asymmetric. The second short-term goal of the program is to investigate the effect of hydrodynamic instabilities that break spherical symmetry: the Standing Accretion Shock Instability (SASI) and neutrino-driven convection. Multi-dimensional simulations at different levels of sophistication will be carried out to clarify the physics of these instabilities in new regimes and the resulting observational consequences. The results will have implications for the expected neutrino- and gravitational wave signal from the next Galactic core-collapse supernova, and will shed light on related astrophysical issues such as the distribution of pulsar spins and kicks at birth.