Gravitational Waves from Compact Bodies

1 According to general relativity theory, compact concentrations of energy (e.g., neutron stars and black holes) should warp spacetime strongly, and whenever such an energy concentration changes shape, it should create a dynamically changing spacetime warpage that propagates out through the Universe at the speed of light. This propagating warpage is called gravitational radiation—a name that arises from general relativity’s description of gravity as a consequence of spacetime warpage. There are a number of efforts, worldwide, to detect gravitational radiation. These efforts are driven in part by the desire to “see gravitational waves in the flesh,” but more importantly by the goal of using the waves as a probe of the Universe and of the nature of gravity. They should be a powerful probe, since they carry very detailed information about gravity and their sources. In this lecture I shall describe the prospects to study gravitational waves from astronomical systems that exist in our Universe today. Such systems are expected to radiate in the “high-frequency” (1—10Hz) and “low-frequency” (10—1Hz) gravitational-wave bands. By contrast, gravitational waves from the early universe (which I shall not discuss here) should populate a far wider band of frequencies, ∼ 10Hz—10Hz. The high-frequency band is the domain of Earth-based gravitationalwave detectors: resonant-mass antennas, and most especially laser interferometers. A number of interesting compact sources fall in this band: the stellar collapse to a neutron star or black hole in our Galaxy and distant