1. H. Stephani, et al. Exact Solutions of Einstein's Field Equations. Cambridge: Cambridge University Press. 2003. ISBN 978-0-521-46136-8.O'Neill, Barrett. The Geometry of Kerr Black Holes. Wellesley, MA: A. K. Peters. 1995. ISBN 978-1-56881-019-5. DOI: https://xs.dailyheadlines.cc/books?hl=zh-CN&lr=&id=No4vOtVj63AC&oi=fnd&pg=PR18&dq=Exact+Solutions+of+Einstein%27s+Field+Equations.+&ots=ThYU2rs1OA&sig=ht8G0DLjhbrPJEtLi2v0aFL0huU.
2. K. Schwarzschild, Über das Gravitationsfeld eines Massenpunktes nach der Einsteinschen Theorie. Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften. 1916, vol 7, pp. 189–196. DOI: https://ui.adsabs.harvard.edu/abs/1916SPAW.......189S/abstract.
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