(ed.). Gravitational waves (IOP, 2001)(422s).

Chapter 4Astrophysics of gravitational-wave sourcesThere are a large number of possible gravitational-wave sources in the observablewaveband, which spans eight orders of magnitude in frequency: from 10 −4 Hz(lower bound of current space-based detector designs) to 10 4 Hz (frequency limitof likely ground-based detectors). Some of these sources are highly relativisticand not too massive, especially above 10 Hz: a black hole of mass 1000M ⊙has a characteristic frequency of 10 Hz, and larger holes have lower frequenciesin inverse proportion to the mass. Neutron stars have even higher characteristicfrequencies. Other systems are well described by Newtonian dynamics, such asbinary orbits.For nearly-Newtonian sources the post-Newtonian approximation (seechapter 6) provides a good framework for calculating gravitational waves. Morerelativistic systems, and unusual sources like the early universe, require moresophisticated approaches (see chapter 7).4.1 Sources detectable from ground and from space4.1.1 Supernovae and gravitational collapseThe longest expected and still probably the least understood source, gravitationalcollapse is one of the most violent events known to astronomy. Yet, because wehave little direct information about the deep interior, we cannot make reliablepredictions about the gravitational radiation from it.Supernovae are triggered by the gravitational collapse of the interiordegenerate core of an evolved star. According to current theory the result shouldbe a neutron star or black hole. The collapse releases an enormous amountof energy, about 0.15M ⊙ c 2 , most of which is carried away by neutrinos; anuncertain fraction is converted into gravitational waves. One mechanism forproducing this radiation could be dynamical instabilities in the rapidly rotatingcore before it becomes a neutron star. Another likely source of radiation is the r-mode instability (see chapter 7). This could release ∼0.1M ⊙ c 2 in radiation everytime a neutron star is formed.43