“School of Astronomy”
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Paper IPM / Astronomy / 14592  


Abstract:  
Numerical studies of gravitational collapse to black holes make use of apparent horizons, which are intrinsically foliationdependent. We expose the problem and discuss possible solutions using the Hawking quasilocal mass. In spherical symmetry, we present a physically sensible approach to the problem by restricting to spherically symmetric spacetime slicings. In spherical symmetry the apparent horizons are gaugeindependent in any spherically symmetric foliation but physical quantities associated with them, such as surface gravity and temperature, are not. The widely used comoving and Kodama foliations, which are of particular interest, are discussed in detail.
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