Superbursts: Multi-dimensional Simulations of Deep Carbon Explosions on Neutron Stars

中子星(NS)是除黑洞以外宇宙中密度最大的天体，自从它们第一次被猜想以来，就一直吸引着理论家和观察家。尽管在过去的40年里，在电磁频谱上进行了大量的观测，但在NS的深处发生的大部分事情仍然是令人费解的。由于太空中的X射线望远镜、实验室的核实验和引力波探测器，如激光干涉仪引力波天文台(LIGO)，中子星物理学的知识正在迅速增长。密歇根州立大学的一个研究小组将使用最先进的多维流体力学计算机代码来模拟NS表面碳的热不稳定点火和由此产生的爆炸(“超级爆发”)，从而帮助天文学家更好地了解中子星。这些模型可以揭示中子星外层的条件，并有助于回答美国国家科学院报告中提出的一些关键科学问题：在极高密度和温度下物质的性质是什么？是什么控制着致密恒星残骸的质量、半径和自转？计划中的工作包括招募下一代科学家和告知公众的活动，公众最终支持这一科学努力。该小组将开发教育资源，使使用开源计算机模拟来探索恒星物理变得更容易，并将获奖期间的发现纳入密歇根州立大学艾布拉姆斯天文馆的公开演讲中。中子星是在有限密度和低温下研究量子色动力学的独特的自然实验室。最近的一些观测、理论和实验发展对中子星的内部构成提出了新的问题。对于中子星吸积富氢或富氦物质的低质量X射线双星，从几秒到几十年的时间尺度上对吸积诱导现象的X射线观测提供了关于中子星不同层的重要信息。在吸积过程中，可以观察到吸积物质失控的热核燃烧，即I型X射线爆发。数以千计的X射线爆发，以及更罕见、能量更高的超暴，编码了关于致密物质的物理以及吸积盘和边界层的工作原理的信息。研究人员将使用点火模型来解释中子星地壳中相关的加热和冷却过程。这些模拟将对从某些来源观测到的前兆爆发和超暴期间光度随时间的演变产生可检验的预测。这些模型将向天文学家通报中子星外层的条件，并可能提供爆炸对吸积流的影响以及致密物质中核火焰的性质的信息。这一奖项反映了美国国家科学基金会的法定任务，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Neutron stars (NS) are the densest objects in the universe, other than black holes, and have fascinated theorists and observers since they were first conjectured. Despite a wealth of observations across the electromagnetic spectrum over the last four decades, much of what happens in the deep interior of NS remains inscrutable. Knowledge of neutron star physics is growing rapidly, due to X-ray telescopes in space, laboratory nuclear experiments, and gravitational wave detectors such as the Laser Interferometer Gravitational Wave Observatory (LIGO). A research group at Michigan State University will help astronomers to better understand neutron stars by modeling the thermally unstable ignition of carbon on the NS surface and the resulting explosion (a "superburst") using a state-of-the-art multidimensional hydrodynamics computer code. The models can reveal conditions in the outer layer of neutron stars, and help answer some critical science questions identified in National Academy reports: what is the nature of matter at exceedingly high density and temperature?, and what controls the mass, radius, and spin of compact stellar remnants? The planned work includes activities to recruit the next generation of scientists and to inform the public, who ultimately support the scientific endeavor. The group will develop educational resources to make it easier to use open-source computer simulations to explore stellar physics and incorporate discoveries made during the award into public talks at Michigan State's Abrams Planetarium.Neutron stars are unique natural laboratories to study quantum chromodynamics at finite density and low temperature. A number of recent observational, theoretical, and experimental developments have raised new questions about the internal constitution of neutron stars. For low-mass X-ray binaries, in which the neutron star accretes hydrogen- or helium-rich material, X-ray observations of accretion-induced phenomena over timescales ranging from seconds to decades provide important information about different layers of the neutron star. During accretion, runaway thermonuclear burning of the accreted material is observable as a Type I X-ray burst. The thousands of X-ray bursts and the rarer and more energetic superbursts encode information about the physics of dense matter and the workings of the accretion disk and boundary layer. The researchers will use ignition models that account for relevant heating and cooling processes in the neutron star crust. The simulations will yield testable predictions for both the precursor burst observed from some sources and the evolution of luminosity with time during the superburst. The models will inform astronomers about conditions in the outer layer of neutron stars, and may give information about the explosion's effect on the accretion flow and the nature of nuclear flames in dense matter.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.