Simulating a Type Ia Supernova
In the July 2007 issue of Sky & Telescope (page 32), science writer David S. Stevenson describes some of the recent progress made by astronomers in figuring out what causes Type Ia supernovae. Most supernova explosions signal the deaths of short-lived massive stars, but Type Ia blasts come from old white dwarfs, which are the Earth-size remnants of longer-lived low-mass stars like our Sun.
As Stevenson explains, an isolated white dwarf simply cools and fades. But a white dwarf in a binary star system may come to a violent end. If it accretes enough material from its stellar companion to reach the so-called Chandrasekhar limit of about 1.4 solar masses, the little star will no longer be able to support its own weight. It will collapse, heat up, and ignite its entire bulk in a nuclear conflagration that will briefly shine as bright as a whole galaxy of stars.
Curiously, the initial stages of the inferno are sometimes decidedly asymmetric. If real white dwarfs explode this way, it could explain some of the differences observed among Type Ia supernovae.
Stevenson's article included some still frames from a supercomputer simulation done at the University of Chicago's Center for Astrophysical Thermonuclear Flashes. You can read more about this simulation in the University of Chicago's press release, and you can watch a video (2.5-megabyte QuickTime movie) by clicking on the image above.
The video covers the first few seconds of a Type Ia supernova. The first sequence shows a two-dimensional slice through the center of an exploding white dwarf. The rings are contours that mark differences in density, and the gray tones represent fuel and ash that is enveloping the star. The second, longer sequence shows a three-dimensional simulation of the blast. Areas of yellow and orange represent flame popping out of the star, while the blue circle marks the star's surface.