Black hole singularities: a new critical phenomenon

The singularitiy 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 $\alpha_{\rm crit}$ exists. For exponents below the critical one ($\alpha<\alpha_{\rm crit}$) 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 ($\alpha>\alpha_{\rm crit}$) 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.