Global Dynamics of Accretion in High-Mass X-Ray Binary Systems

天空中一些最壮观的X射线源是高质量X射线双星（HMXB）。在这些系统中，一个紧凑的物体，如中子星星或黑洞，快速地绕着一颗热的、年轻的、大质量的星星旋转。致密天体的引力将物质从星星中拉出来，然后这些物质螺旋式地落在致密天体上，产生明亮的X射线辐射。 PI和他的团队将运行计算机模拟，以更好地了解有多少物质福尔斯落在紧凑的伴星上，以及有多少物质逃离了双星的引力场并消失在星际空间中-这个数量是了解HMXB如何演变的关键。这项工作将有助于解释目前的观测HMXB的相关观测性质的传质速率。 这项研究的大部分将由本科生完成，并将用于向不同的年轻学生群体介绍天体物理学研究。除了他们的研究，学生们还将在北卡罗来纳州自然科学博物馆展示他们的作品，并与北卡罗来纳州图书馆数字媒体实验室的工作人员一起创作YouTube短片。 PI将继续建立一系列关于流体动力学和计算物理的简短（10分钟）视频课程，帮助学生开始这种研究，更多的高年级学生将介绍一些课程。研究人员将使用一个新的环双星气体动力学代码来研究HMXB中质量和角动量吸积的全球动态，以将观测结果与这些系统的演变和分类相关的系统参数联系起来。这项工作将重点关注像船帆座X-1这样的观测良好的系统，以及从Be X射线双星到超巨星快速X射线瞬变和吸积黑洞系统的广泛系统。通过将星周气体动力学的数值模型（例如，洛希瓣溢出，来自施主星星的潮汐增强风的加速，风的X射线加热和光致电离）和吸积流（在保持角动量的同时跟随气体到小半径），研究人员已经开发了一个环双星气体动力学代码，可以提高我们对HMXB各种性质的理解。这项工作将使三维引力吸积流的模拟具有足够的细节，以定性地描述任何动力学不稳定性的起源，并定量地描述在各种情况下吸积到致密伴星上或从系统中丢失的质量和角动量的通量。基金会的学术价值和更广泛的影响审查标准。

Some of the most spectacular X-ray sources in the sky are High Mass X-ray Binaries (HMXBs). These are systems where a compact object, such as a neutron star or a black hole, rapidly orbits a hot, young, massive star. The gravitational pull of the compact object pulls material from the star which then spirals onto the compact object producing bright X-ray emission. The PI and his team will run computer simulations to better understand how much material falls onto the compact companion vs. how much escapes the gravitational field of the binary and is lost to interstellar space – this quantity is key for understanding how HMXBs evolve. This work will aid the interpretation of current observations of HMXBs by relating observational properties to the mass transfer rate. Much of this research will be done by undergraduates and will be used to introduce a diverse group of young students to astrophysics research. In addition to their research, the students will present their work at the North Carolina Museum of Natural Sciences and work with staff at the Digital Media Lab in the NC State library to create short YouTube videos. The PI will continue to build a series of short (10 minute) video lessons on fluid dynamics and computational physics that help students get started in this kind of research, with more senior students presenting some of the lessons. The investigator will use a new circumbinary gas dynamics code to investigate the global dynamics of mass and angular momentum accretion in HMXBs to connect observations to system parameters relevant to the evolution and classification of these systems. This work will focus both on well-observed systems like Vela X-1 as well as the broad class of systems ranging from Be X-ray binaries to supergiant fast X-ray transients and accreting black hole systems. By coupling together numerical models of the circumstellar gas dynamics (e.g., Roche lobe overflow, acceleration of the tidally enhanced wind from the donor star, X-ray heating and photoionization of the wind) and of the accretion flow (following the gas to small radii while conserving angular momentum), the investigators have developed a circumbinary gas dynamics code that can improve our understanding of the varied properties of HMXBs. This effort will enable simulations of gravitational accretion flows in three dimensions with sufficient detail to qualitatively describe the origin of any dynamical instability and to quantitatively characterize the resulting flux of mass and angular momentum accreted onto the compact companion or lost from the system in a variety of circumstances.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.