Not every star can be black hole. This state black hole can be realize for objects whose radius a is close to Schwarzshild radius r_ = 2GM/c^2, It is easly to calculate yhat for planets and and most number of sars r_g ,, a. The condition r_g = a can be realized for neutron stars, quasars and pulsars/, It is evidently that these objects posses very great densities( approximately 10^14 g/cm^3). Some these objects rotate very quickly. This rotation lets to cutch masses of near nearly located usual stars< dust ... It is evidently that the Sun and the Earth cannot be black holes, because theirs r?g