March 19, 2013
Chandra Helps Astronomers Identify Kepler Supernova Triggers
April Flowers for redOrbit.com - Your Universe Online
NASA's Chandra X-ray Observatory has identified the cause of Kepler's supernova, the famous explosion first discovered by Johannes Kepler in 1604. The image above shows low (red), intermediate (green) and high (blue) energy X-rays with a star field background from the Digitized Sky Survey.
It is already known that the supernova is a Type Ia, which is the thermonuclear explosion of a white dwarf star. Type Ia's are important cosmic distance markers for tracking the accelerated expansion of the universe.
There is an ongoing controversy concerning Type Ia supernovas, however. Scientists question if they are caused by a white dwarf pulling so much material from a companion star that it becomes unstable and explodes, or do they result from the merger of two white dwarfs?
The Kepler supernova was triggered by an interaction between a white dwarf and a red giant star according to the new Chandra analysis. A disk-shaped structure near the center of the remnant provided the crucial evidence. The research team interpreted this X-ray emission to be caused by the collision of supernova debris and disk-shaped material expelled from the giant star before the explosion.
The disk structure observed by Chandra in X-rays is very similar to one observed in the infrared by the Spitzer Space Telescope in both shape and size. This composite image, with the disk structure labeled, shows the Chandra data from iron emission in blue, and the Spitzer data in pink. A long and puzzling concentration of iron on one side of the structure is revealed by the image, leading the researchers to speculate that the cause of this asymmetry might be the "shadow" in iron that was cast by the companion star, which blocked the ejection of material. Theoretical work of the past has suggested this shadowing as a possibility for Type Ia supernova remnants.
The research team created this animation of a simulated supernova explosion interacting with material expelled by the giant star companion. It had been assumed that the bulk of this material was expelled in a disk-like structure. This structure would have a gas density ten times higher at the equator, running from left to right, than the density of the poles. The simulation was created in two-dimensions and then projected into three dimensions to create an image that the team could compare with the Chandra and Spitzer observations. The team's interpretation of the data was supported by the agreement of the simulation with the observations.
Results of the study are published in the Astrophysical Journal.