Recent Results on Rest Frames for Radiating Isolated Systems

OSVALDO M. MORESCHI

Gravitational Waves: A Challenge to Theoretical Astrophysics

The Abdus Salam ICTP

Año: 2001; p. 345 - 355

The gravitational waves, that are expected to be observed with the new generation of detectors, are supposed to be generated by systems involving very compact objects during processes like the coalescence of binary systems. First order estimation of the gravitational radiation emitted by those systems can be carried out from the quadrupole formula. More precise description of the gravitational radiation requires improved formulae which would probably take into account further multipole structure of the sources. This conduces immediately to the issue of which is the appropriate frame of reference that should be used to define the multipole structure of the system. Even the notion of angular momentum is dependent on the frame that one is using to make the calculation. For example, if one uses an inappropriate frame, which is moving and is not round, to describe the asymptotics of Schwarzschild spacetime, one could find a nonzero angular momentum and a complicated multipole structure. Instead, when one wishes to describe the gravitational radiation, one is interested in determining the intrinsic structure of the sources, and therefore intends to avoid information associated to an inappropriate choice of frame. In few words, one is interested in using a frame that captures the idea of being at rest with the sources, which is round around the sources and that is centered in relation to the central distribution. All these properties are required to be satisfied at all times; whish is not a trivial requirement for systems in which the back reaction due to gravitational radiation are important. The appropriate reference frame at future null infinity are constructed using the so called ´nice sections´ that we have introduced some time ago. In this occasion we would like to report on our latest results on our program; which allow us to provide a notion of center of mass frame, which is used to define intrinsic angular momentum, and can also be used to describe the multipolar structure of the sources of gravitational waves.