SOME PHYSICAL CONSEQUENCES OF ABRUPT CHANGES IN THE MULTIPOLE MOMENTSOF A GRAVITATING BODY

The Barrabes-lsrael theory of lightlike shells in general relativity i s used to show explicitly that in general a lightlike shell is accompa nied by an impulsive gravitational wave. The gravitational wave is ide ntified by its Petrov-type N contribution to a Dirac delta-function te rm in the Weyl conformal curvature tensor (with the delta function sin gular on the null hypersurface history of the wave and shell). An exam ple is described in which an asymptotically flat static vacuum Weyl sp ace-time experiences a sudden change across a null hypersurface in the multipole moments of its isolated axially symmetric source. A lightli ke shell and an impulsive gravitational wave are identified, both havi ng the null hypersurface as history. The stress-energy in the shell is dominated (at large distance from the source) by the jump in the mono pole moment (the mass) of the source with the jump in the dipole momen t mainly responsible for the stress being anisotropic. The gravitation al wave owes its existence principally to the jump in the quadrupole m oment of the source confirming what would be expected.