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arXiv 2512.06930gr-qc
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重新审视暗物质晕中的黑洞:关于爱因斯坦方程一致解的探讨

Revisiting black holes in dark-matter halos: on consistent solutions to the Einstein equations

RUDN University(俄罗斯人民友谊大学)

S. V. Bolokhov

AI总结:

本文探讨了暗物质晕中黑洞的爱因斯坦方程解问题,指出牛顿近似在致密天体附近的有效性受限,并提出了一致的构造框架。

摘要:

近年来有几篇论文声称构建了描述被暗物质晕包围的黑洞的爱因斯坦方程解,这些解使用了如Navarro-Frenk-White、Burkert、Einasto、伪等温以及溶质分布等经验驱动的密度分布。我们证明了用于获得许多这些度量的通用方法通常并不能得到正确描述所声称物质源的爱因斯坦方程的解。这个问题源于在相对论框架内直接应用牛顿关系将切向速度与包含质量联系起来,随后进行任意假设$g(r)=f(r)$对于度量函数。这种做法导致了一种各向异性流体,其压力为$P_r=-ρ$和$P_t=-rρ'/2-ρ$,其密度与所声称的晕分布不同,且在视界附近常常变得非物理,违反了弱能量条件。因此,所获得的时空并不描述嵌入已知银河晕中的黑洞,而是与所设想物质分布无关的其他各向异性配置。我们通过文献中的几个代表性例子来展示这个问题,包括基于NFW、Burkert、Einasto、溶质、伪等温以及Dehnen-(1,4,5/2)分布的度量,以及NGC~4649晕的情况。对于每个案例,提供了正确的爱因斯坦一致的度量形式及其相关的物理解释。我们的分析澄清了牛顿近似在致密天体附近有效性的局限性,并建立了在广义相对论内构建暗物质启发的黑洞几何结构的一致框架。

英文摘要:

A number of recent papers have claimed to construct solutions of Einstein's equations describing black holes surrounded by dark-matter halos with empirically motivated density profiles such as the Navarro-Frenk-White, Burkert, Einasto, pseudo-isothermal, and solitonic distributions. We show that the approach used to obtain many of these metrics generically does not lead to the correct solutions to the Einstein equations for the matter sources they purport to represent. This issue originates from applying the Newtonian relation between the tangential velocity and the enclosed mass directly within a relativistic framework, followed by the ad hoc assumption $g(r)=f(r)$ for the metric functions. This procedure leads to an anisotropic fluid with $P_r=-ρ$ and $P_t=-rρ'/2-ρ$, whose density differs from the claimed halo profile and often becomes non-physical near the horizon, violating the weak energy condition. As a result, the obtained spacetimes do not describe black holes embedded in known galactic halos but rather distinct anisotropic configurations unrelated to the intended matter distribution. We demonstrate this problem on several representative examples from the literature, including metrics based on the NFW, Burkert, Einasto, solitonic, pseudo-isothermal, and Dehnen-(1,4,5/2) profiles, as well as the case of the NGC~4649 halo. For each case, the correct Einstein-consistent form of the metric and the associated physical interpretation are provided. Our analysis clarifies the limits of validity of the Newtonian approximation near compact objects and establishes a consistent framework for constructing dark-matter-inspired black-hole geometries within General Relativity.

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