Scalar-type gravitational wave emission from gravitational collapse in Brans-Dicke theory: Detectability by a laser interferometer.

Abstract

To investigate the possibility of obtaining evidence for scalar-tensor theories of gravity by laser interferometric gravitational wave observatories (e.g., LIGO), we perform numerical simulations of the gravitational collapse of a spherically symmetric dust fluid and investigate the waveform and amplitude of scalar-type gravitational waves (SGW's) in the Brans-Dicke theory, which is one of the simplest scalar-tensor theories. We find that in the case of the dust collapse of mass \ensuremath{\sim}10${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ and initial radius \ensuremath{\sim}100--1000 km, the emitted SGW's have a maximum amplitude \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}22}$(500/\ensuremath{\omega})(10 Mpc/R) and a characteristic frequency \ensuremath{\sim}40--1000 Hz. This means that if the gravity theory is the Brans-Dicke theory with \ensuremath{\omega}\ensuremath{\lesssim} several thousands, the advanced LIGO may detect a signal of SGW's from a supernova at the Virgo cluster. And, if we happen to find a supernova in our Galaxy, we may detect SGW's even if \ensuremath{\omega} is as large as \ensuremath{\sim}${10}^{6}$. Concerning cosmic censorship, we also investigate the fate of a collapsed object. Our numerical results suggest that the final product of a collapsed object is a black hole in the Brans-Dicke theory like in the Einstein theory, and outside the black hole, the Brans-Dicke scalar field seems to become constant. These results support the cosmic censorship conjecture.