Dense Matter in Compact Stars

致密恒星中的致密物质

• 批准号: ST/M005046/1
• 负责人: Andreas Schmitt
• 金额: $ 49.84万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2015
• 资助国家: 英国
• 起止时间: 2015 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FM005046%2F1
• 关键词: Dense; Matter; Compact; Stars

Compact stars are, after black holes, the densest objects in the universe. They are as heavy as the sun, but their radius is only about 10 km. Their extreme density makes compact stars a perfect "laboratory" for fundamental physics. The reason is that when matter is squeezed more and more, at some point the relevant degrees of freedom are no longer atoms, but rather neutrons and protons or - possibly relevant for the center of a compact star - quarks. In other words, we can learn something about our fundamental theories of nature by relating astrophysical observations to predictions from the microscopic theory. And, we can turn the argument around and learn something about the star ("What is a compact star made of?") by computing observable quantities from fundamental theories. This interplay between astrophysics and particle physics is at the core of the proposed research. One main line of my research will be the study of "stellar superfluids" and their hydrodynamic properties. The underlying mechanism for superfluidity (and superconductivity) is very general: just like helium-3 atoms or electrons, the fermions in a compact star may form Cooper pairs. Therefore, it is very likely that in the interior of a compact star, nuclear matter and quark matter become superfluid (they can also be superconducting, for instance in a phase where protons form a Cooper pair condensate). In contrast to the superfluids in an ordinary laboratory, the stellar superfluids are of relativistic nature, at least deep inside the star. It is thus one main objective of my research to connect a microscopic, field-theoretical description of relativistic superfluids with astrophysical observables that are sensitive to whether matter is superfluid or not. Such an observable is for instance the rotation frequency: some stars rotate about 1000 times per second; this is remarkable because we know that there are certain instabilities which tend to slow down the star's rotation (by emitting gravitational waves at the same time). In order to understand the necessary damping of these instabilities, a thorough understanding of the hydrodynamic properties of dense matter is mandatory. In particular, viscous effects in a superfluid are very different from viscous effects in a normal fluid. Compact stars are not only very dense and rotate very fast, but can also have enormously large magnetic fields. In this case, they are called magnetars. Again, this is very interesting from the fundamental point of view: magnetic fields, if sufficiently large, may influence or even dramatically change the properties of fundamental matter. For instance, one may ask whether a star that would be entirely made of ordinary nuclear matter in the absence of a magnetic field contains a core of quark matter in the presence of a magnetic field. It is an ongoing effort in current research to understand such changes in the phase structure theoretically. One long-term theoretical goal is to "map out" the phases of Quantum Chromodynamics not only in the plane of temperature and baryon density, but in a three-dimensional phase diagram that also contains the magnetic field. Compact stars sit somewhere in this three-dimensional space.

致密星是宇宙中仅次于黑洞的致密天体。它们和太阳一样重，但它们的半径只有10公里。它们的极端密度使致密恒星成为基础物理学的完美“实验室”。原因是当物质被挤压得越来越厉害时，在某个点上，相关的自由度不再是原子，而是中子和质子，或者--可能与致密星星的中心有关--夸克。换句话说，我们可以通过将天体物理学观测与微观理论的预测联系起来，来了解我们关于自然的基本理论。而且，我们可以把争论转过来，了解一些关于星星的东西（“紧凑的星星是由什么组成的？“）通过计算基础理论中的可观测量。天体物理学和粒子物理学之间的这种相互作用是拟议研究的核心。我的研究的一条主线将是“恒星超流体”及其流体动力学性质的研究。超流性（和超导性）的基本机制非常普遍：就像氦-3原子或电子一样，致密星星中的费米子可以形成库珀对。因此，在致密星星的内部，核物质和夸克物质很可能成为超流体（它们也可以是超导的，例如在质子形成库珀对凝聚体的阶段）。与普通实验室中的超流体不同，恒星超流体具有相对论性质，至少在星星内部是如此。因此，我的研究的一个主要目标是将相对论性超流体的微观场论描述与对物质是否是超流体敏感的天体物理观测值联系起来。这样的一个可观测量是例如旋转频率：有些恒星每秒旋转大约1000次;这是值得注意的，因为我们知道存在某些不稳定性，这些不稳定性往往会减缓星星的旋转（通过同时发射引力波）。为了理解这些不稳定性的必要阻尼，必须彻底理解致密物质的流体动力学性质。特别是，超流体中的粘性效应与正常流体中的粘性效应非常不同。紧凑型恒星不仅密度很大，旋转速度很快，而且还可能具有巨大的磁场。在这种情况下，它们被称为磁星。同样，从基本的观点来看，这是非常有趣的：磁场，如果足够大，可能会影响甚至戏剧性地改变基本物质的性质。例如，人们可能会问，一颗在没有磁场的情况下完全由普通核物质组成的星星，在有磁场的情况下是否包含一个夸克物质的核心。从理论上理解这种相结构的变化是当前研究的一个持续努力。一个长期的理论目标是不仅在温度和重子密度的平面上，而且在包含磁场的三维相图中“绘制”出量子色动力学的相。致密恒星位于这个三维空间的某个地方。

项目成果

Mixing of charged and neutral Bose condensates at nonzero temperature and magnetic field

带电和中性玻色凝聚在非零温度和磁场下的混合

• 发表时间: 2017
• 作者: Haber A

Baryon onset in a magnetic field

• DOI: 10.1063/1.4938699
• 发表时间: 2014-12
• 作者: A. Haber;F. Preis;A. Schmitt

New color-magnetic defects in dense quark matter

• DOI: 10.1088/1361-6471/aabc1a
• 发表时间: 2017-12
• 期刊: arXiv: High Energy Physics - Phenomenology
• 作者: A. Haber;A. Schmitt

Dissipation Triggers Dynamical Two-Stream Instability

• DOI: 10.3390/particles2040028
• 发表时间: 2019-08
• 期刊: Particles
• 影响因子: 1.4
• 作者: N. Andersson;A. Schmitt

Strange quark mass turns magnetic domain walls into multi-winding flux tubes

奇异夸克质量将磁畴壁变成多绕组通量管

• DOI: 10.1088/1361-6471/abcb9d
• 发表时间: 2021
• 期刊: Nuclear and Particle Physics
• 作者: Evans G