标题： 关于极限紧致对象的工作坊：黑洞和 Buchdahl 星球 显示英文标题

标题： Workshop on the limiting compactness objects: Black holes and Buchdahl stars

摘要： 此次工作坊于2023年10月30日至11月3日在IUCAA举办，是一次紧凑的讨论与交流会议，详细探讨了各种方面及其引发的问题。 此次工作坊是由瑞典哥德堡工业大学的安德松教授的访问促成的。他和他的合作者已经探索爱因斯坦-瓦尔索夫系统超过十五年，作为致密天体可能的物质来源。 这个系统的特点是自由粒子运动且仅通过引力相互作用。 对于极限致密性来说，这可能是最合适的模型。 工作坊的主要目的是理解这种新的致密星， 即没有视界的Buchdahl星（BS）。它几乎和黑洞（BH）一样致密，但没有视界，因此可以与外界互动。 自从膜范式设想黑洞视界附近的类时基准面以来，BS为这种真实天体物理对象的存在提供了极好的可能性。 它可以很好地模仿黑洞来解释各种物理和天体物理现象。 因此，它为研究和探讨所有关于黑洞的问题开辟了一个全新的视野，尤其是针对这个新生物——BS。 工作坊旨在确定一些有趣的问题以及对这些问题感兴趣的研究人员。 在这方面，工作坊取得了巨大的成功，因为已经确定了一些有趣的问题，几个小组被组建起来解决不同的问题，并且工作已经开始。 从这样的活动中，不可能再要求更多了。 其中包括一些报告的简要总结，随后是工作坊期间讨论后确定的一些项目的简要讨论。 显示英文摘要

摘要： The workshop was organized at IUCAA on Oct 30 - Nov 3, 2023 as a compact discussion and discourse meeting with a threadbare exposition and discussion of the various aspects and the questions arising. It was occasioned by the visit of Professor Hakan Andreasson of the Gothenburg Technical University, Sweden. He has been exploring with his collaborators the Einstein - Vlasov system for over a decade and a half as a possible matter source for compact objects. This system characterizes itself by free particles in motion and interacting only through gravity. For a limiting compactness, this may be the most appropriate state. The main thrust of the workshop was to understand this new object, Buchdahl Star (BS), of limiting compactness without a horizon. It is almost as compact as a black hole (BH) and yet has no horizon and hence is open for interaction with the outside world. Ever since the proposal of the membrane paradigm envisaging a timelike fiducial surface near BH horizon, BS offers an excellent possibility of the existence of such a real astrophysical object. It could very well compete with BH as a mimicker for various physical and astrophysical phenomena. Thus, it opens up a new vista of study and investigation of all the questions that one asks for BH, for this new creature, BS. The workshop was intended to identify certain interesting questions as well as the people interested in studying them. On this count, the workshop has been a huge success as several interesting questions have been identified, a few groups have been formed to take up different problems, and the work has already started. Nothing more could one have asked from such an exercise. A brief summary of some of the talks is included, followed by a brief discussion of the projects identified as a result of the discussions during the workshop.