Astrophysical Black Holes in the Physical Universe
Shuang-Nan Zhang
备注：
15 figures, 23 pages. A book chapter in Astronomy Revolution: 400 Years of Exploring the Cosmos (York, D. G., Gingerich, O., Zhang S. N. eds), Taylor & Francis Group LLC/CRC Press, 2011
In this chapter I focus on asking and answering the following questions: (1) What is a black hole? Answer: There are three types of black holes, namely mathematical black holes, physical black holes and astrophysical black holes. An astrophysical black hole, with mass distributed within its event horizon but not concentrated at the singularity point, is not a mathematical black hole. (2) Can astrophysical black holes be formed in the physical universe? Answer: Yes, at least this can be done with gravitational collapse. (3) How can we prove that what we call astrophysical black holes are really black holes? Answer: Finding direct evidence of event horizon is not the way to go. Instead I propose five criteria which meet the highest standard for recognizing new discoveries in experimental physics and observational astronomy. (4) Do we have sufficient evidence to claim the existence of astrophysical black holes in the physical universe? Answer: Yes, astrophysical black holes have been found at least in some galactic binary systems, at the center of almost every galaxy, and as the central engines of at least some long gamma-ray bursts. (5) Will all matter in the universe eventually fall into black holes? Answer: Probably "no", because "naked" compact objects, if they do exist with radii smaller than the radii of event horizons for their masses but are not enclosed by event horizons, can rescue the universe from an eternal death by re-cycling out the matter previously accreted into astrophysical black holes. Finally I also discuss briefly if we need a quantum theory of gravity in order to further understand astrophysical black holes, and what further astronomical observations and telescopes are needed to make further progress on our understanding of astrophysical black holes.
Beginning a journey across the universe: the discovery of extragalactic neutrino factories
中微子是宇宙中最难以捉摸的粒子，几乎可以不受阻碍地穿越宇宙。尽管收集了大量的数据，但一个长期存在且未解决的问题仍然是高能中微子与产生它们的天体物理来源之间的联系。在中微子的候选来源中，有耀变体，这是一类由超大质量黑洞提供动力的河外来源，这些黑洞提供指向地球的高度相对论喷流。先前的研究似乎存在争议，一些努力声称高能中微子事件和单个耀变体之间存在暂时的联系，而其他人则对这种关系提出质疑。在这项工作中，我们表明耀变体与高能天体物理中微子的关联是毫无疑问的，其置信度达到了前所未有的水平，即概率为6 x 10^{-7}。我们的统计分析提供了观测证据，耀变体是天体物理中微子工厂，因此，河外宇宙射线加速器。
On the Solution to the "Frozen Star" Paradox, Nature of Astrophysical Black Holes, non-Existence of Gravitational Singularity in the Physical Universe and Applicability of the Birkhoff's Theorem
Astrophysical Black holes: An Explanation for the Galaxy Quenching
Ahmedabad University（艾哈迈达巴德大学）；UM-DAE Centre for Excellence in Basic Sciences (CEBS)（基础科学卓越中心（CEBS））；Max Planck Institute for Radio Astronomy（马克斯·普朗克射电天文研究所）；University of Alabama（阿拉巴马大学）
Electric charge estimation of a new-born black hole
虽然理论上黑洞可以具有非常大的电荷（$Q/(\sqrt{G} M) \simeq 1$），但实际天体物理学黑洞的电荷通常被认为是可以忽略的。这个假设是基于这样一个事实：天体物理学上的黑洞总是被一些等离子体包围着，而等离子体是一种非常好的导体。然而，它忽略了黑洞通常有一些角动量，这可以解释为它的某种旋转。如果在孔周围的等离子体中存在某种磁场，则会导致产生电场，从而导致电荷分离。本文估计了恒星质量天体物理黑洞的电荷上限。我们考虑了一个新的黑洞的形成过程，并证明了一个新的黑洞的电荷可以是显著的（$\sim 10^{13}$ {库仑}）。虽然天体物理黑洞的电荷很大，但荷质比$Q/(\sqrt{G} M) \sim 10^{-7}$很小，不足以对恒星的引力场或坍缩动力学产生显著影响。
Lensing by black holes within astrophysical environments
National Technical University of Athens（雅典国立技术大学）；National Observatory of Athens（雅典国家天文台）；Universitat d’Alacant（阿利坎特大学）；University of Tübingen（蒂宾根大学）；Instituto Superior Técnico – IST, Universidade de Lisboa – UL（里斯本大学高等理工学院）
Observational evidence for the formation of trapping horizons in astrophysical black holes
在广义相对论中，黑洞的特征是它们的捕获视界，一种只能向内穿过的单向膜。在天体物理学上，黑洞中的俘获视界的存在可以用反证法（reductio ad absurdum argument）在观测上进行检验，用具有物理表面的无视界结构代替黑洞，并寻找与电磁波和引力波观测不一致的地方。在这种方法中，无水平线物体的半径总是大于但任意接近相同质量的黑洞的视界所在的位置。这些替代方案的半径上限已提供使用电磁观测（在光学/红外波段）的天文源在星系中心，但缺乏下限，留下不受约束的巨大区域的参数空间。我们在这里表明，下限的半径不发展捕获地平线的地平线上的物体，可以放置使用观测吸积系统。这个结果与模型无关，只依赖于由无视界物体周围的时空几何所决定的局部因果关系概念。这些观测范围大大减少了以前允许的参数空间，提高了利用电磁观测建立陷阱视界存在的前景。
A Four-dimensional Model-agnostic Probe into the Astrophysical Origins of Binary Black Hole Subpopulations
Northwestern University（西北大学）；NSF-Simons AI Institute for the Sky (SkAI)（美国国家科学基金会-西蒙斯人工智能天空研究所）；Department of Physics and Astronomy, Northwestern University（西北大学物理与天文学系）
Can AI Understand Our Universe? Test of Fine-Tuning GPT by Astrophysical Data
International Center for Relativistic Astrophysics (ICRA)（国际相对论天体物理中心）；International Center for Relativistic Astrophysics Network (ICRANet)（国际相对论天体物理网络中心）；University of Science and Technology of China（中国科学技术大学）；University of Padova（帕多瓦大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；ICRANet-Armenia（国际相对论天体物理网络中心亚美尼亚分部）；Isfahan University of Technology（伊斯法罕理工大学）
