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CRII: ACI: Unveiling the Origin of the Highest Energy Particles in the Universe with Large-Scale First-Principle Fully-Kinetic Simulations

CRII：ACI：通过大规模第一原理全动力学模拟揭示宇宙中最高能量粒子的起源

基本信息

批准号：
1657507
负责人：
Lorenzo Sironi
金额：
$ 17.07万
依托单位：
Columbia University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-07-01 至 2020-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1657507&HistoricalAwards=false
关键词：
CRII ACI Unveiling Origin Highest

项目摘要

The long-term objective of this project is to unveil the origin of the highest energy particles in the Universe - the so-called ultra-high-energy cosmic rays (UHECRs) --- charged ions whose energies can exceed the energy of a tennis ball. Since the highest energy ions are extremely rare, their origin still remains elusive. One of the leading candidates for UHECR production are blazars, a class of galaxies with relativistic jets emerging from supermassive black holes. However, the processes that can accelerate UHECRs in blazar jets are not fully understood. Most models attempt to infer the properties of the accelerated particles by fitting the observed emission from blazars. Due to the large number of free parameters, the models are not uniquely constrained by the observations and, therefore, have little predictive power. In fact, there is no reliable theory built from first principles for the mechanism that transfers the jet energy to the highest energy particles, and so there is no definite answer to whether UHECRs originate from blazar jets. This proposal aims to address this fundamental problem - thus, serving NSF's mission to promote the progress of science - by studying the physics of particle acceleration in blazar jets from first principles. The proposed program will also create research opportunities for undergraduate students of Astronomy, Computer Science and Physics departments. In the process, the students will be exposed to an active research environment and trained in the scientific method. An interactive website will be developed with the goal of providing the public an easy access to this exciting field of multidisciplinary research (at the interface between computing, physics and astronomy). The website will also provide a portal for high school teachers interested in updating their lectures with current scientific findings. The proposed project will investigate the origin of UHECRs by studying self-consistently the physics of particle acceleration in the relativistic jets of blazars. The research will explore particle acceleration in magnetic reconnection - a process by which magnetic field lines of opposite polarity annihilate, releasing their energy to the particles. The physics of particle acceleration is highly non-linear - the reconnection process affects the overall jet dynamics, which in turn changes the efficiency of energy dissipation via reconnection - and therefore hard to model with analytical tools. The project takes advantage of the enormous growth of computing power in the last few years and the development of powerful Particle-In-Cell (PIC) codes that can model collisionless plasmas from first principles. The investigation of particle acceleration will be performed via a suite of 2D and 3D PIC simulations in unprecedentedly large domains, so that the results can be properly extrapolated from the microscopic scales of PIC simulations to the macroscopic scales of astrophysical accelerators. As the plasma composition in blazar jets is not well constrained, project will investigate the efficiency of proton acceleration in both electron-proton and electron-positron-proton plasmas. A novel cooling module for the particles will be implemented in the PIC code, to account self-consistently for the effect of radiative losses on the electron and proton dynamics (i.e., synchrotron radiation and photohadronic interactions with radiation fields in the jet). This will be of significant importance to assess whether blazar jets can accelerate ions up to ultra-high energies.

该项目的长期目标是揭示宇宙中最高能量粒子的起源-所谓的超高能宇宙射线（UHECR）-带电离子，其能量可以超过网球的能量。由于最高能量的离子非常罕见，它们的起源仍然难以捉摸。其中一个主要的候选者是耀变体，这是一类从超大质量黑洞中产生相对论喷流的星系。然而，可以加速耀变体喷流中UHECR的过程还没有完全了解。大多数模型试图通过拟合观测到的耀变体的辐射来推断加速粒子的性质。由于大量的自由参数，模型不是唯一的约束的观察，因此，有很少的预测能力。事实上，对于将喷流能量转移到最高能量粒子的机制，并没有可靠的理论，因此对于UHECR是否起源于耀变体喷流也没有明确的答案。这项提案旨在解决这一基本问题-因此，服务于NSF的使命，以促进科学的进步-通过研究从第一原理的粒子加速在blazar喷流的物理。该计划还将为天文学，计算机科学和物理学系的本科生创造研究机会。在这个过程中，学生将接触到一个积极的研究环境，并在科学方法的培训。将开发一个交互式网站，目标是为公众提供一个方便的多学科研究的这一令人兴奋的领域（在计算，物理和天文学之间的接口）。该网站还将为有兴趣用最新科学发现更新其讲座的高中教师提供一个门户。拟议的项目将通过自洽地研究耀变体相对论喷流中粒子加速的物理学来调查UHECR的起源。这项研究将探索磁重联中的粒子加速--这是一个相反极性的磁力线湮灭的过程，将它们的能量释放给粒子。粒子加速的物理学是高度非线性的-重连过程影响整体射流动力学，这反过来又改变了通过重连耗散能量的效率-因此很难用分析工具建模。该项目利用了过去几年计算能力的巨大增长和强大的粒子单元（PIC）代码的发展，可以从第一原理模拟无碰撞等离子体。粒子加速的研究将通过一套2D和3D PIC模拟在前所未有的大域中进行，因此结果可以从PIC模拟的微观尺度适当地外推到天体物理加速器的宏观尺度。由于blazar喷流中的等离子体成分没有得到很好的限制，项目将研究电子-质子和电子-正电子-质子等离子体中质子加速的效率。PIC代码中将实现用于粒子的新型冷却模块，以自洽地考虑辐射损失对电子和质子动力学的影响（即，同步辐射和光强子与喷流中辐射场的相互作用）。这对于评估耀变体喷流是否能够将离子加速到超高能量具有重要意义。