Gravitational wave emission from core collapse of massive stars

We derive estimates for the characteristics of gravitational radiation from stellar collapse, using recent models of the core collapse of Chandrasekhar-massed white dwarfs (accretion-induced collapse), core-collapse supernovae and collapsars, and the collapse of very massive stars (greater than or similar to300 M-circle dot). We study gravitational wave emission mechanisms using several estimation techniques, including two-dimensional numerical computation of quadrupole wave emission, estimates of bar-mode strength, estimates of r-mode emission, and estimates of waves from black hole ringing. We also review the rate at which the relevant collapses are believed to occur, which has a major impact on their relevance as astrophysical sources. Although the latest supernova progenitor simulations produce cores rotating much slower than those used in the past, we find that bar-mode and r-mode instabilities from core-collapse supernovae remain among the leading candidate sources for second-generation detectors at the Laser Interferometer Gravitational-Wave Observatory (LIGO II). Accretion-induced collapse (AIC) of a white dwarf could produce gravitational wave signals similar to those from core collapse. In the models that we examine, such collapses are not unstable to bar modes; we note that models recently examined by Liu & Lindblom, which have slightly more angular momentum, are certainly unstable to bar formation. Because AIC events are probably 1000 times less common than core-collapse supernovae, the typical AIC event will be much farther away, and thus the observed waves will be much weaker. In the most optimistic circumstances, we find that it may be possible to detect gravitational waves from the collapse of 300 M-circle dot Population III stars.