Critical behavior and scaling in vacuum axisymmetric gravitational collapse

We report a second example of critical behavior in gravitational collapse. Collapse of axisymmetric gravitational wave packets is computed numerically for a one-parameter family of initial data. A black hole first appears along the sequence at a critical parameter value p^*. As with spherical scalar-field collapse, a power law is found to relate black-hole mass (the order parameter) and critical separation: M₁₇-p^*^. The critical exponent is 0. 37, remarkably close to that observed by Choptuik. Near-critical evolutions produce echoes from the strong-field region which appear to exhibit scaling.