The Angular Resolution of Space-Based Gravitational Wave Detectors

The era of gravitational astronomy is nearly here. In the next few years, ground-based laser gravitational wave detectors will begin to come on line and, it is hoped, space-based detectors will soon follow. Even if the ground-based detectors do not succeed in detecting the waves within the next decade, the space-based detectors will certainly be able to, so the physics goal of the detection of the new phenomenon will be achieved one way or the other, and gravitational wave detectors will then move from being physics experiments to being tools of observational astronomy. It can be argued that the frequency band accessible to the space detectors is the more interesting one, both experimentally and observationally. It is here, at frequencies between 10−4 Hz and 1 Hz, that identified individual sources (such as AM CVn) exist, thus guaranteeing the detection of the phenomenon. But it is also at these frequencies that astronomical objects of the greatest observational interest are to be found, objects for which only gravitational astronomy can provide data that bears on critical astrophysical and cosmological questions. In this paper, we will investigate the ability of space-based detectors to determine the locations in the sky of two of these kinds of astronomical sources—close compact binaries in the Galaxy and coalescing massive black hole binaries in the nuclei of galaxies at high redshift.