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Supernova explosions
stay in shape

Posted: December 18, 2009

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New research finds that studying the shape of the aftermath of supernovae could allow astronomers to classify the mechanism of stellar explosion.

The new research is based on images from NASA's Chandra X-ray Observatory and shows that the shape of the debris flung out in supernova explosions at the end of a star's life sheds light on how the star exploded in the first place, even hundreds or thousands of year's later.

These two supernova remnants are part of the new study that shows how the shape of the remnant is connected to the way the progenitor star exploded. On the left is a remnant tied to the core-collapse mechanism, while the more 'organised' explosion of a Type 1a is shown at right. Image: NASA/CXC/UCSC/L. Lopez et al.

“It’s almost like the supernova remnants have a ‘memory’ of the original explosion,” says Laura Lopez of the University of California at Santa Cruz. “This is the first time anyone has systematically compared the shape of these remnants in X-rays in this way.”

Supernovae types are usually based on the properties observed in the days following the explosion and reflect different physical explosion mechanisms such as core-collapse or the explosion of a white dwarf star. For the new study Lopez and colleagues focused on relatively young supernova remnants that exhibit strong X-ray emission from silicon so as to rule out the effects of interstellar matter surrounding the explosion. The results showed that X-ray images of the ejected debris 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 and found that information on the explosion mechanism is also reflected in the type of elements observed in it. For example, Type 1a supernovae – caused by the thermonuclear explosion of a white dwarf – left behind relatively symmetric, circular remnants, whereas “core-collapse” supernova (when a very massive, young star collapses onto itself) left more asymmetric debris.

“If we can link supernova remnants with the type of explosion then we can use that information in theoretical models to really help us nail down the details of how the supernovas went off,” says co-author Enrico Ramirez-Ruiz.

In this study, ten of the 17 remnants were classified as core-collapse, and seven as Type 1a. However, one case-study seemed to share properties of both types: SNR 0548-70.4 was considered a Type Ia based on its chemical abundances, but Lopez finds it has the asymmetry of a core-collapse remnant.

“We do have one mysterious object, but we think that is probably a Type Ia with an unusual orientation to our line of sight,” says Lopez. “But we’ll definitely be looking at that one again.”

The paper describing these results appeared in the November 20 issue of The Astrophysical Journal Letters.

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