1. English Translation of “the Foundation of the General Theory of Relativity”;Einstein,2015
2. On the gravitational field of a mass point according to Einstein’s theory;Schwarzschild,1999
3. The Escape of Photons from Gravitationally Intense Stars
4. Les Houches Summer School of Theoretical Physics: Black Holes;Bardeen,1973
5. Curvature radius and Kerr black hole shadow