New images from NASA's Chandra X-ray Observatory show that the symmetry of supernova remnants, or lack thereof, reveal how the original stars exploded. Astronomers say the discovery is important because it will help them better classify supernovas that exploded hundreds or thousands of years ago. The discovery is reported in a new Astrophysical Journal Letters study.

Astronomers sort supernovas into several categories, or "types", based on properties observed days after the explosion and which reflect very different physical mechanisms that cause stars to explode.  But, since observed remnants of supernovas are leftover from explosions that
occurred long ago, other methods are needed to accurately classify the original supernovas.

The Researchers focused on the relatively young supernova remnants that exhibited strong X-ray emission from silicon ejected by the explosion so as to rule out the effects of interstellar matter surrounding the explosion.  Their analysis showed that the X-ray images of the ejecta can be used to identify the way the star exploded.  The team studied 17 supernova remnants both in the Milky Way galaxy and a neighboring galaxy, the Large Magellanic Cloud.

A new study of images from Chandra shows that the symmetry of the supernova remnants, or lack thereof, reveals how the star exploded. G292.0+1.8 (left) represents a type of supernova where a massive star collapses on itself. The shape of this type of remnant is relatively asymmetric. The Kepler supernova remnant (right) is from a family of supernovas produced by a thermonuclear explosion on a white dwarf. Kepler and other remnants like it are more symmetrical in shape thanG292 and its brethren. (Photo Credit: NASA/CXC/UCSC/L. Lopez et al.)

For each of these remnants there is independent information about the type of supernova involved, based not on the shape of the remnant but, for example, on the elements observed in it.  The researchers found that one type of supernova explosion - the so-called Type Ia - left
behind relatively symmetric, circular remnants.  This type of supernova is thought to be caused by a thermonuclear explosion of a white dwarf, and is often used by astronomers as "standard candles" for measuring cosmic distances.

"It's almost like the supernova remnants have a 'memory' of the original explosion," said Laura Lopez of the University of California at Santa Cruz, who led the study.  "This is the first time anyone has systematically compared the shape of these remnants in X-rays in this way."

Citation: L. A. Lopez, E. Ramirez-Ruiz, C. Badenes, D. Huppenkothen, T. E. Jeltema, D. A. Pooley, 'TYPING SUPERNOVA REMNANTS USING X-RAY LINE EMISSION MORPHOLOGIES', Astrophysical Journal Letters, Nov. 2009, 706 L106-L109; doi: 10.1088/0004-637X/706/1/L106