Simulation of a binary white dwarf merger
The idea of using a ray-tracer to simulate stellar scenery is attractive because, in principle, it should be possible to simulate a lot of real physics in a natural way. For example the concepts of absorption, scattering and reflection are already built into the software. However there are difficulties.
Light sources: POV-Ray works with point sources of light. Although POV-Ray light sources can "look_like" an extended object, the rays still emanate one from point. Alternatively, "area_lights" can be chosen, but these are planar arrays of point sources.
A real star consists of a spherical light source (the photosphere where the continuum is formed) superimposed by a scattering layer (an atmosphere) responsible for phenomena such as limb darkening and absorption lines. To resemble a real star, our simulation should have a colour which reflects the colour (effective) temperature of the photosphere and demonstrate some limb darkening.
Experiments were made with different types of object comprising a central light source and hollow spheres and/or shells filled with a coloured scattering medium. None of these has been entirely satisfactory. For example, in order for the central light source to illuminate the surface, the star must be transparent. Consequently light from a binary companion will be added to the self light on all surfaces.
I have compiled a POVRay include file containing some of the experimental stars I have built. Here's a list of the objects declared, without comment at present. I hope to add more details later.
Simulation source code
The POVRay source for creating the white dwarf binary merger movie is given for demonstration purposes.We have a second movie, of the sdB+KIII binary HD185510, which was created by a colleague, Scott Manley. It is particularly interesting for its simulation of a spotted star surface, the reflection effect of the hot star shining onto the cool star, and the use lenses and flares to create a realistic scene. POVRay has evolved since that was built, and the source no longer works.
In trying to recreate the scene I started to develop a code for emulating "any "binary system from a definition of masses, period,radii and temperatures. I have not yet had time to tidy this up - so, for example, the eclipses don't yet hide the flare from the eclipsed star - and there is much more to do (Roche geometry would be nice!). The source is made available in case bits are useful to other animation developers.
This page is maintained by:
Simon Jeffery (firstname.lastname@example.org)
Last modified: 31/07/01