Neutron Star Astrophysics

中子星是在超新星中诞生的引人注目的天体，当一颗大质量恒星在其生命末期坍塌时。这颗大质量恒星的核心在自身引力的作用下会收缩，直到半径只有10公里，但其质量仍与太阳相当。中子星内部的中子和质子之间的距离比原子核中的更近，因此中子星是研究强核力的重要实验室。中子星也很重要，因为它们附近的极端条件：强重力、强磁场和快速自转。*这里提出的研究是对中子星内部和周围的物理过程的调查。目标是找出中子星内部的致密物质是什么样子，了解为什么许多中子星是磁性活跃的(就像我们的太阳的极端版本)，并将中子星作为实验室来研究极端条件。为此，我们建立了我们认为发生在中子星内部的过程的理论模型，然后与天文观测进行比较，通常是使用轨道X射线望远镜。*特别令人感兴趣的是双星系统中的中子星。如果中子星的轨道距离它的伴星足够近，伴星表面上升的巨大潮汐会导致气体流向中子星。氢和氦在中子星表面积聚了几个小时，然后经历了一次热核失控，迅速燃烧起来，产生了持续几秒钟的明亮X射线。在这几秒钟内，我们可以直接看到中子星并对其进行研究。这个方案中的一个项目是了解恒星在经历其中一次闪光时从恒星表面驱动的等离子风。通过观察X射线，我们可以尝试测量中子星的半径，并从那里计算出它的核心密度。*一些中子星具有很强的磁场，并显示出与太阳类似的耀斑和喷发。这相当令人惊讶，因为中子星应该有一个相对平静的表面，而不是太阳的外层是对流的，所以等离子体不断地向上鼓泡到表面，干扰磁场。不知何故，中子星也是磁性活跃的。我们希望通过研究加热事件后中子星冷却的速度来找出其中的原因。

Neutron stars are remarkable objects born in supernovae when a massive star collapses at the end of its life. The core of the massive star shrinks under its own gravity until it is only 10km in radius, but still contains as much mass as the Sun. The neutrons and protons inside the neutron star are closer together than in the nucleus of an atom, and so neutron stars are important laboratories for studying the strong nuclear force. Neutron stars are also important because of the extreme conditions in their vicinity: strong gravity, strong magnetic fields, and rapid spin. ******The research proposed here is an investigation of physical processes in and around neutron stars. The goal is to find out what the dense matter inside neutron stars is like, understand why many neutron stars are magnetically active (like an extreme version of our Sun), and to use neutron stars as laboratories to investigate extreme conditions. We do this by making theoretical models of processes that we think are happening inside neutron stars and then comparing to astronomical observations, often with orbiting X-ray telescopes. ******Of particular interest are neutron stars in binary systems. If the neutron star orbits close enough to its companion star, the huge tides raised on the surface of the companion cause gas to flow onto the neutron star. The hydrogen and helium builds up on the surface of the neutron star for a few hours and then undergoes a thermonuclear runaway, rapidly burning up and causing a bright flash of X-rays lasting a few seconds. For those few seconds, we can see the neutron star directly and study it. One of the projects in this proposal is to understand the plasma wind that is driven from the surface of the star as it undergoes one of these flashes. By observing in X-rays, we can try to measure the radius of the neutron star and from there work out the density of its core. ******Some neutron stars have strong magnetic fields and show flares and eruptions similar to our Sun. This is quite surprising because a neutron star should have a relatively calm surface, unlike the Sun whose outer layers are convective so that plasma is continuously bubbling up to the surface and disturbing the magnetic field. Somehow neutron stars are also magnetically active. We hope to find out why by studying how quickly the neutron star cools down after a heating event.**