Gravitational Waves from the Merging of White Dwarfs

Binary white dwarfs emit gravitational waves with frequencies of up to a few mHz. As a consequence of the loss of angular momentum both components gradually approach and the gravitational waves emitted by the system increase both in amplitude and frequency (it is said that they chirp). In fact, the chirp of the galactic white dwarf binary population is expected to be the dominant source of noise at low frequencies. A fraction of these binaries, those separated by a distance smaller than roughly three solar radii, will eventually merge in a time shorter than a Hubble time. It is expected that during the merging they will emit gravitational waves transporting extremely valuable information about the coalescing process. Although the phase of chirping can be accurately calculated analytically, the merging demands a full three-dimensional numerical treatment because of the nature of the problem. There are additional reasons to study the merging of two white dwarfs in a binary system. Firstly, if the total mass is larger than the Chandrasekhar mass the outcome of the merging can be a Type Ia supernova or an accretion induced collapse. Secondly, it has also been suggested that they can be at the origin of some hot and massive white dwarfs that are presumably members of the galactic halo.