Black-hole singularities: a new critical phenomenon.

The singularity inside a spherical charged black hole, coupled to a spherical, massless scalar field is studied numerically. The profile of the characteristic scalar field was taken to be a power of advanced time with an exponent alpha>0. A critical exponent alpha(crit) exists. For exponents below the critical one (alpha<alpha(crit)) the singularity is a union of spacelike and null sectors, as is also the case for data with compact support. For exponents greater than the critical one (alpha>alpha(crit)) an all-encompassing, spacelike singularity evolves, which completely blocks the "tunnel" inside the black hole, preventing the use of the black hole as a portal for hyperspace travel.