The black holes in the gravitational event of the Laser Interferometer Gravitational-wave Observatory

On February 11th, 2016, the Laser Interferometer Gravitational-wave Observatory (LIGO) announced the shocking science news: the gravitational wave predicted 100 years ago by Einstein is finally detected! And this event GW150914 came from the merging of two stellar mass black holes! There have been massive public and professional media coverage on this event, and thus this paper will answer from different perspectives several questions about the black holes that generated the observed gravitational waves, such as, why did not Einstein believe the existence of black holes? How to know such objects are black holes? How does matter fall into a black hole? How to obtain independent evidence that such gravitational wave events indeed come from merging black holes? How can our understanding of black holes be improved with the detection of such gravitational events?