本文介绍第54届国际物理奥林匹克竞赛理论考试的第三题.该题的名称是黑寡妇脉冲星，表面上与2024年亚洲物理奥林匹克竞赛理论第三题类似，而本质是关于双星体系的吸积与单个气体星体的平衡的典型力学题.题目分成两个部分，第一部分关注双星体系质量的转移（吸积）；第二部分是单个气体星体，在气体压力和重力作用下的平衡问题.题目利用的是力学中的典型模型，整体中规中矩，这也是本届理论题目的共性.

This paper discusses the theoretical problem 3 of the 54th International Physics Olympiad (IPhO). The title of the problem is called Black Widow Pulsar. At glance it appears similar to the APho (Asia Physics Olympiad) 2024 theoretical problem 3, however the essence is a typical mechanics problem about the accretion of binary star system and the equilibrium of a single gas star. The question is composed of two parts, first is concerned with the transfer of mass (accretion) in a binary star system; the second is the equilibrium of a single gaseous star, under the influence of gas pressure and gravity. It utilizes classical models in mechanics and decent in difficulty and quite suitable for high school Olympiad students. This is common feature for this 54th IPhO. A detailed description and answer to this problem is given here.