Co-Evolution of Cosmic Rays and Thermal Plasma in Galaxy Clusters

这个项目将探索星系团中宇宙射线的物理和观测结果。星系团形成于宇宙历史的早期，并通过从其外围吸引物质和偶尔与其他星系团合并而不断增长。随着物质的增加，它会产生热量，就像流星穿过地球大气层时被加热一样。与此同时，星系团中心的超大质量黑洞周围的环境以壮观的爆发方式喷出物质和能量。所有这些热量、物质和能量被注入的介质是等离子体——一种完全电离的气体，它非常热，不会发出可见光，而是发出x射线。在这个等离子体中，大约一百亿分之一的带电粒子是宇宙射线——能量如此之大，以至于它的传播速度接近光速。这个项目的目标是解开这种质量和能量输入的复杂舞蹈，了解它是如何产生等离子体和宇宙射线混合物的，并预测它将如何出现在现有的和未来计划的射电、x射线和伽马射线望远镜的镜头下。该项目还将为来自传统上代表性不足的群体的研究生和本科生提供研究培训。对星系团的x射线观测显示，大约40%的重子物质以普遍存在的10 - 100 keV等离子体的形式存在，被称为星系团内介质（ICM）。ICM携带一个具有纠缠拓扑结构的磁场，并承载着能量显著的相对论性宇宙射线，这些宇宙射线在无线电频率上被观察到，并且预计会在强子起源的伽马射线中被探测到，令人困惑的是从未被发现过。理解ICM中的能量分配和输运，从星系团外围的全球尺度引力落入和中心的超大质量黑洞活动，到在没有频繁库仑碰撞的情况下出现的微尺度波和不稳定性，是一个多尺度非平衡等离子体物理问题。直到最近，由于先进的计算资源和算法的突破，使得ICM等离子体的数值模拟几乎可以从第一性原理开始，这一进展才成为可能。由威斯康星大学麦迪逊分校的教职员工领导的研究生和本科生团队将与洛斯阿拉莫斯国家实验室的科学家合作，利用这些机会首次对热等离子体、相对论宇宙射线和湍流的共同演化进行全面建模。预计计算的辐射输出将导致详细的预测，这些预测将通过无线电、x射线和伽马射线观测进行验证。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will explore the physics and observational consequences of cosmic rays in galaxy clusters. Clusters of galaxies formed early in the history of the Universe, and are still growing by pulling in matter from their outskirts and occasionally merging with other clusters. As matter is added, it creates heat, much as meteors are heated as they fall through the atmosphere of the Earth. At the same time, the environments surrounding supermassive black holes at the centers of galaxy clusters spew forth matter and energy in spectacular bursts. The medium into which all this, heat, matter, and energy are poured is a plasma – a fully ionized gas so hot that instead of emitting visible light, it glows in x-rays. About one in ten billion of the charged particles within this plasma is a cosmic ray - so energetic that it travels at nearly the speed of light. The goal of this project is to unravel this complex dance of mass and energy input, understand how it creates a plasma and cosmic ray mixture, and predict how it will appear under the lens of radio, x-ray, and gamma-ray telescopes existing now and planned for the future. The project will also provide research training for graduate and undergraduate students from traditionally under-represented groups.X-ray observations of galaxy clusters reveal that about 40% of their baryonic matter is in the form of a pervasive, 10 – 100 keV plasma known as the Intracluster Medium (ICM). The ICM carries a magnetic field with tangled topology and hosts an energetically significant population of relativistic cosmic rays, which are observed at radio frequencies and were expected to be detected in gamma-rays of hadronic origin, which puzzlingly have never been seen. Understanding energy partitioning and transport in the ICM, from global scale gravitational infall at the cluster outskirts and supermassive black hole activity at the center, to the microscale waves and instabilities that thrive in the absence of frequent Coulomb collisions, is a multi-scale non-equilibrium plasma physics problem. Progress has only recently become possible due to advanced computing resources and algorithmic breakthroughs that enable numerical simulation of ICM plasma almost from first principles. A team of graduate and undergraduate students led by faculty members at the University of Wisconsin - Madison collaborating with scientists at the Los Alamos National Laboratory will use these opportunities to comprehensively model, for the first time, the joint evolution of thermal plasma, relativistic cosmic rays, and turbulence. Radiative outputs of the calculations are expected to lead to detailed predictions that will be tested by radio, x-ray, and gamma-ray observations.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.