The Interior of Black Holes and their Astrophysics

Gravity warps space and time into a funnel and generates a black hole when a cosmic body undergoes a catastrophic collapse. What can one say about the interior of a black hole? The important point is that inside a black hole the space radial direction becomes time, and time becomes a space direction. The path into the gravitational abyss of the interior of a black hole is a progression in time. There is a peculiar region inside a black hole where some characteristics of the space-time curvature become singular. We call this region singularity. The colossal tidal gravitational forces near singularity modify physical laws. Space and time are not only strongly curved near the singularity, but they split into quanta. The fall into the singularity is unstoppable for a body inside a black hole. This paper also addresses the following questions: Can one see what happens inside a black hole? Can a falling observer cross the singularity without being crushed? Can new baby universes arise inside a black hole? An answer to all these questions is probably ``yes''. We give also a brief review of the modern black hole astrophysics.