Gravitational wave radiation from single and binary white dwarfs

Resumen

In the next few years the first generation of gravitational wave detectors will become a reality, opening this way a new observational window into Astronomy. It is essencial then to have a complete set of detailed models of gravitational wave emission to which compare the results that migh be obtained by such detectors, and particulary by the space-borne gravitational wave detector LISA, wich will be likely launched by 2014. On the other hand, white dwarfs are compact objects wich can emmit gravitational waves if they were found in a binary system or in the pulsational instability stripe. Under some circumstances, this gravitational waves will be strong enough to be detected. This is the reason why in the present thesis the gravitational wave emission from pulsating and binary white dwarfs has been studied. In the first case we have studied the gravitational wave emission from three different types of non- radial pulsations presents in white dwarfs: the g,r and p modes. It has been shown that for g modes, where the main restoring force is gravity, the gravitational wave emission is by far too week to be observed by the LISA detector. On the other hand, for the p modes, where the main restoring force is pressure, we have shown that gravitational wave emission will become so intense that pulsations will be inmediately absorved. In the second case, the gravitational wave emission from the coalescence of binary systems has been calculated. Using an SPH code the coalescence of a series of binary sytems has been calculated, covering a broad set of masses and initial conditions, wich are fully representative of the different type of galactic binary systems. Using this results we have been able to calculate in detail the gravitational wave emission during the collision phase, and simultaneously, other astrophysically interesting characteristics of the merging of white dwarfs. In particular we have been able to show that galactic binary systems of white dwarfs will be a guaranteed sources for the LISA detector, not only as background noise generators but also as isolated detectable events. Additionally, we have studied the observational consequences of this type of events, in order to serve as high energy electromagnetic counterparts for the gravitational wave detectors. We have also analized the viability of the doubly degenerate escenario (DD) as a type Ia supernova progenitor, wich is another reason why the coalescence of binary systems of white dwarfs is extremely interesting. In particular, we have been able to show that the resulting density and temperature distributions, in the cases where two different mass stars were involved, difficults the viability of the scenario. It has to be finally notticed, that all this work has required a big computational efffort only possible by the improvements that have been introduced in the SPH code. In particular, a new prescription for the artificial viscosity has been introduced. The code has also been parallelized in order to be able to run high resolution simulations in a feasible time.