At a very early age, children learn how to classify objects according to their shape. Now, new research suggests studying the shape of the aftermath of supernovas may allow astronomers to do the same.

A new study of images from NASA's Chandra X-ray Observatory on supernova remnants - the debris from exploded stars - shows that the symmetry of the remnants, or lack thereof, reveals how the star exploded.

"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."

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.

Lopez and colleagues 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.

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.

"Supernovas that come from thermonuclear explosion on white dwarfs (known as Type Ia) produce very symmetric remnants. Another type, created when a very massive star collapses, results in more asymmetrically shaped remnants. (Credit: NASA/CXC/UCSC/L. Lopez et al.)"

Source: Chandra X-ray Center