PROBING NEUTRON STARS PHYSICS USING NASA'S NICER MISSION

摘要：“中子星(NSS)是致密天体。微小的NSS直径不超过20-30公里，但质量是太阳的1-3倍，代表了极端的重力、压力和密度，使它们成为唯一在外部燃烧物质的恒星。幸运的是，一些NS有亲密的伴星；来自这些恒星的气体，被致密的天体强引力吸引，向它漏斗和螺旋形移动，形成一个吸积盘。这些系统被称为NS低质量X射线双星(LMXB)；我们从它们观察到的最强大的现象与这些吸积盘直接相关，因为当物质接近致密天体时，会释放出大量的引力能量。这会导致内部吸积盘达到高达1亿度的温度，从而发射出光谱中X射线波段的大部分能量。正是这种凝聚的等离子体流到了NS上，这提供了极少数的机会来直接探测微小(几公里)区域的性质，在那里我们可以在其他无法进入的区域中看到广义相对论效应的作用。在这个项目中，我们将利用来自中子星内部成分探测器(NICER)的高时间和高能量分辨率的X射线数据来了解只有在NS附近才能看到的毫秒X射线变化的物理学。“

Summary: "Neutron stars (NSs) are compact objects. The tiny NSs being no more than 20-30 km in diameter but containing masses of 1 to 3 times the Sun, represent extremes of gravity, pressure and density, making them the only stars where matter burns on the outside. Fortunately, some NS have close companion stars; gas from these stars, attracted by the compact object strong gravity, funnels and spirals towards it, forming an accretion disk. These systems are called NS low-mass X-ray binaries (LMXBs); the most powerful phenomena we observe from them are directly related to these accretion disks, as a large amount of gravitational energy is released when the matter approaches the compact object. This causes the inner accretion disk to reach temperatures as high as 100 million degrees and therefore to emit the bulk of the energy in the X-ray band of the spectrum. It is the flow of this accreting plasma onto the NS which provides one of the very few opportunities to directly probe the properties of the tiny (few km) regions where we can "see" General Relativity effects in action in otherwise inaccessible regimes. During this project, we will make use of high-time and high-energy resolution X-ray data from the Neutron star Interior Composition Explorer (NICER) to understand the physics of millisecond X-ray variations seen only around NS. "