INNERMOST STABLE ORBITS FOR COALESCING BINARY-SYSTEMS OF COMPACT OBJECTS

The innermost stable circular orbits of binary systems of non-rotating, compact objects of arbitrary mass ratio are studied in the absence of gravitational radiation reaction. The method uses two-body equations of motion that are valid through (post)2-Newtonian order (order [(Gm/rc2)2]), but that also include test body effects in the Schwarzschild geometry exactly. The harmonic coordinate separation of the innermost stable orbit varies from the test body value of 5m to about 6m for equal masses, where m is the total mass. The orbital energy, angular momentum and frequency of the innermost stable orbit are also determined as a function of the ratio of the two masses. Implications of the results for detection of gravitational radiation by laser-interferometer gravitational observatories are discussed.