Double white dwarfs

AM CVn stars
Ultra-compact X-ray

Black hole binaries
SN Ia progenitors
Gravitational waves
LISA wiki (verification

My thesis

Progenitors of type Ia supernovae

Type Ia supernovae are very bright objects that appear in the sky and are understood as exploding white dwarfs. They are used to map the expanions of the Universe and are the main producers of Iron. The white dwarfs likely explode because they grow in mass to the Chandrasekhar mass, the mass above which the degenracy pressure cannot withstand gravity any more. The compression then triggers the ignition of nuclear burning, which in degenerate matter leads to runaway and explosion. The big question is what is causing the white dwarf to grow in mass to the Chandrasekhar mass? Is it slow accretion from a hydrogen rich companion and are the progenitors thus cataclysmic variables, symbiotic stars or supersoft X-ray sources, or is the merging of two white dwarfs

Possible progenitor of type Ia supernova 2007on

We approached this issue in a way that potentially allows us to directly observe the progenitors of type Ia supernovae. We search the archives for images taken before the supernova for all newly discovered supernovae that are of type Ia and nearby enough that the progenitors may be visible.

In From Voss & Nelemans, 2008 we report the discovery of an X-ray source very close to the position of the type Ia supernova 2007on. Below is tha false colour X-ray image of the region. The object is clearly one of the softest sources, as is expected from a supersoft source. Intriguingly, there are also a number of rather hard photons detected.

False colour X-ray image of the position where supernova 2007on exploded, taken before the explosion. The possible progenitor is the pink obect in the center of the image. From Voss & Nelemans, 2008

Follow-up observations have shown that there is a small but distinct offset between the measured positions of the X-ray sourc and the supernova. Detailed analysis shows that the probability of finding such an offset is comparable to the chance alignment probability. Only further observations will be able to settle this issue. See this submitted paper for more information

Image showing the pre-supernova X-ray source (left) and a Swift observation of the supernova in November 2007. Image credit Chandra press office.

Chandra press release
Dutch press release

SN 2005E a new type of Supernova

Supernova 2005E was found to be a peculiar supernova: a type Ib supernova in a very old population. Type Ib supernovae are supposed to be the core collapse of a massive star and thus should explode in a young populations. Further research showed that the best explanation of this supernova is explosive helium burning, eihter as we predicted in the so-called .Ia SN, or the merger of a helium and a C/O white dwarf.

Nature article Perets et al. 2010
Dutch press release