CAREER: The Composition of Dense Matter and Observations of Neutron Stars

质量大于8倍太阳质量的恒星会在一种叫做核心坍缩超新星的爆炸中结束生命。如果原始恒星的质量在太阳的8到20倍之间，超新星就会留下一颗中子星。中子星是密度极高的天体，质量与太阳相当，直径约为15英里。正常物质由电子和原子核组成的原子组成，原子核由中子和质子组成，而中子和质子又由上下夸克组成。然而，中子星中心的引力足以将中子和质子紧紧地压缩在一起，以至于中子和质子可能被迫转化为含有奇异夸克的奇异粒子。中子星中是否存在奇异夸克的问题，以及关于密度极高物质的性质的更普遍的问题，是核物理学界和天体物理学界面临的一些主要问题。这个项目旨在回答这些问题，并确定中子星中心的物质性质，在那里重力将物质压缩到水密度的一千万亿倍。本项目为学生和博士后提供培训机会。社区外展包括通过工作室物理课程的持续发展，参与研究和基于网络的中子星可视化来教育学生。核实验和对中子星的观测已经成功地对原子核中心密度附近和以上密度的物质状态方程产生了新的约束。然而，我们目前对高密度的理解是有限的：我们还不知道基态的组成。该项目将核理论与核数据和中子星观测相结合，以确定中子星核心的组成。强相互作用物质的现代模型将与新的富中子核的核结构计算相结合，以构建最先进的中子星外壳和核心模型。这些模型及其伴随的不确定性将用核数据进行校准，并与中子星的冷却、质量和半径观测结果进行比较。例如，中子星的冷却数据已经给出了由较大的质子与中子比引起的快速冷却的迹象。该项目将研究质子-中子比的后验概率分布，以及其他一些将深入了解中子星组成的观测数据。本研究由美国国家科学基金会物理部理论核物理项目和天文科学部共同资助。

Stars with masses greater than eight times the mass of the sun end their lives in an explosion called a core-collapse supernova. If the original star is between eight and twenty times the mass of the sun, the supernova leaves behind a neutron star. Neutron stars are ultra-dense objects with the mass of the sun and a diameter of about 15 miles. Normal matter is made of atoms consisting of electrons and nuclei, nuclei are made of neutrons and protons, and neutrons and protons, in turn, are made of up and down quarks. The gravitational force in the center of a neutron star, however, is sufficient to compress neutrons and protons together so tightly that neutrons and protons may be forced to convert into exotic particles containing strange quarks. The question of whether or not strange quarks are present in neutron stars, and the more general question of the nature of extremely dense matter, are some of the principal questions facing the nuclear physics and astrophysics communities. This project aims to answer these questions and to determine the nature of matter in the center of neutron stars where gravity compresses matter to a thousand trillion times the density of water. This project involves training opportunities for students and postdoctoral fellow. Community outreach includes the education of students through the continued development of a Studio Physics course, involvement in research, and a web-based visualization of neutron stars.Nuclear experiments and observations of neutron stars have successfully generated novel constraints on the equation of state of matter at densities near and above the central densities in atomic nuclei. However, our current understanding of high-densities is limited: we do not yet know the composition of the ground state. This project uses a combination of nuclear theory matched to nuclear data and neutron star observations to determine the composition of neutron star cores. Modern models of strongly-interacting matter will be combined with new nuclear structure calculations of neutron-rich nuclei in order to construct state of the art models of the neutron star crust and core. These models, and their concomitant uncertainties, will be calibrated with nuclear data and compared with neutron star cooling, mass, and radius observations. For example, neutron star cooling data has already given indications of fast cooling arising from a large proton-to-neutron ratio. This project will study the posterior probability distribution for the proton-to-neutron ratio and several other observables that will give insights into neutron star composition. This proposal is co-funded by the Theoretical Nuclear Physics Program in the Physics Division and the Division of Astronomical Sciences at NSF.