Degenerate Dwarf Binaries as Promising, Detectable Sources of Gravitational Radiation
C. R. Evans, I. Iben, Jr., and L. Smarr, Astrophysical Journal, 323, 129-139 (1987).
Abstract
Recent theoretical work suggests the presence in our Galaxy of a large population of degenerate dwarf binaries (DDBs) which have orbital separations small enough that the components are brought into contact by gravitational radiation emission on time scales from 105 to 101 0 yr. In the last e-folding time prior to merger, those systems closest to Earth will individually produce periodic gravitational wave (GW) amplitudes of the order of h 1 x 10- 21 in the frequency range 10-100 mHz. A recent preliminary design for a space based laser interferometer indicates that sources of this kind, are potentially detectable. We discuss the characteristics likely to be seen in such an antenna from degenerate dwarf binaries, assuming theoretical birth rates. At low frequencies the signal is dominated by superposition of unresolved binaries which produce an effective continuum. At high frequencies, individual binaries should be resolvable above the continuum.
In addition to the periodic signal emitted during orbital decay, DDBs may also emit burst signals of several types. Depending on system parameters, the less massive component may transfer mass on a dynamic time scale once Roche lobe contact occurs. It is expected that the lighter component will be transformed into a massive disk or giant envelope about the more massive component, with a concomitant rapid diminution of the periodic GW signal. If the total mass of the system exceeds the Chandrasekhar mass, the subsequent process of merging may lead to collapse of the primary to a neutron star, especially if the heavier dwarf is composed of oxygen and neon, or to a star disrupting explosion with a resultant Type I supernova optical display, if the dwarfs are composed of carbon and oxygen. In either case, the high spin rate that the more massive component may be expected to acquire during the accretion process introduces nonsphericities. Hence, GW emission would occur during either implosion or explosion of the dwarf. If a neutron star forms, rotation rates comparable with the 1.5 ms pulsar, PSR 1937 +21, might occur, producing a near maximum strength gravity wave signal.