[1] J. R. Oppenheimer and H. Snyder, “On Continued Gravitational Contraction,” Physical Review, Vol. 56, No. 5, 1939, pp. 455-459.
[2] Zhang Yongli, “Introduce to Relativity,” The Publishing Company of Yunnan People, Kunming, 1989, p. 388.
[3] L. B. Feng, X. C. Liu and M. C. Li, “Genarel Relativity,” Jilin Science Publishing Company, Jilin, 1995, p. 109.
[4] S. W. Hawking and G. F. R. Eills, “The Large Scale Structure of Space Time,” Cambridge University Press, New York, 1972.
[5] R. E. Schild, D. J. Leiter and S. L. Robertson, “Black Hole or Meco: Decided by a thin Luminous Ring Structure Deep within Quasar Q0957 + 561,” Journal of Cosmology, Vol. 6, 2010, pp.1400-1437.