White Dwarf Binaries: Supernovae Ia progenitors, LISA and X-ray source

Ashley Ruiter

White dwarfs are the most numerous of all compact objects, outnumbering neutron stars and black holes. Binary systems consisting of two white dwarfs are expected to be abundant in the universe, and play an essential role in the occurrence of some of the most interesting astrophysical phenomena. My thesis will address a variety of these issues. I will study the three following topics:

1. The origin and evolution of binary systems (involving white dwarf accretors) leading up to the formation of Type Ia Supernovae progenitors. I will assess which types of systems are the most likely to be precursors to SN Ia events. I will compare the predictions of SN Ia delay times and rates from my detailed population synthesis/evolutionary model to available observations of SN Ia (i.e., Strolger et al.; Mannucci).

2. Using the StarTrack population synthesis code I will identify the important formation channels and analyze the physical characteristics of Galactic double white dwarfs which will be detectable with the LISA gravitational wave observatory. I (and collaborators) will also calculate the gravitational radiation signal arising from this population, and determine the frequency at which this signal becomes confusion-limited.

3. With population synthesis methods, I will study Galactic faint X-ray sources (e.g., 1000s of unidentified point sources in the Galactic centre region observed with Chandra) which are believed, but not yet shown, to be interacting binary systems involving white dwarf accretors.

Assessing the gravitational radiation signal arising from Galactic double white dwarfs, both interacting (i.e., possible X-ray sources) and detached binaries, will aid in the development of signal detection techniques and instrument design for LISA science. In addition, some of the white dwarf binaries detectable with LISA may be potential progenitors of SN Ia. Deciphering which evolutionary processes play the most critical roles in SN Ia progenitors is not a fully explored problem in astrophysics, though constraining these uncertainties is important, as SN Ia play a significant role in chemical evolution of galaxies and are used as `standard candle' cosmological distance indicators, though their origins remain unknown.