THIN SPHERICAL-SHELLS

The equation of motion of a thin spherical timelike shell is obtained directly from the Lanczos equations for all spherically symmetric embedding four-geometries. No explicit form for the intrinsic surface energy three-tensor of the shell is used. It is shown that for static embedding geometries the condition of positive-definite total proper shell mass guarantees the impossibility of the coalescence of inner and black-hole horizons but allows the coalescence of black-hole and cosmological horizons. © 1979 The American Physical Society.