Dr Stephan Rosswog
Professor of Astrophysics
Jacobs University Bremen
Campus Ring 1
D-28759 Bremen, Germany
Tel: +49 421 200-3226
email: s.rosswog@jacobs-university.de







Encounters of two White Dwarfs


Background

White Dwarfs:

  • typical low-mass stars (like our sun) end up as White Dwarfs
  • their mass distribution has a strong peak around 0.6 solar masses
  • typical White Dwarf radii are similar to the Earth's radius
  • typical densities are as high as 106 g/ccm, but can be much higher for high-mass white dwarfs
  • at the Chandrasekhar mass (about 1.4 solar masses) the White Dwarf becomes unstable and starts to collapse
  • the fate of the White Dwarf after collapse may depend on the specific circumstances: it may end up as a neutron star in an "accretion-induced collapse" or it may thermonuclearly ignite in a "type Ia supernova"

    Type Ia supernovae

  • type Ia supernovae are precious tool for observational cosmology to measure large-scale distances in the Universe
  • type Ia supernovae are caused by the thermonuclear ignition of a white dwarf in a binary system, but it is still debated whether a single White Dwarf reaches the Chandrasekhar mass (by accretion from a "normal" binary companion) and explodes after collapsing ("single degenerate scenario") or whether it is caused by a White Dwarf binary that merges under emission of gravitational waves. It is also possible that the class of type Ia supernovae is less homogeneous than previously thought and that actually different catastrophic white dwarf events lead to thermonuclear explosions



    It is important to distinguish two cases:


    Mergers of a double white dwarf binary Collisions of white dwarfs
    example of a binary merger 0.6 and 0.9 solar masses example of a head-on collision between a 0.4 and 0.9 solar mass white dwarf
    Where? Binary systems in the Galaxy Where? Crowded places such as cores of globular clusters and the centres of galaxies
    Relevance? possible progenitor of type Ia supernova; depending on mass also accretion-induced collapse
    to a neutron star, production of "odd" White Dwarfs and possibly very carbon rich stars     		Relevance? currently under investigation ...
    Reference Yoon, Podsiadlowski, Rosswog, MNRAS, 380, 933 (2007) Reference Rosswog et al. to be submitted (2008)