There Is a Mysterious Reverse Shock Wave Supernova Exploding Backwards

Image of the Cassiopeia A reverse Shock Wave.

A powerful shock wave traveling through a cloud of gas left by a star’s explosive death has a strange quirk: It’s traveling in the wrong direction, a new study shows.

According to the study, a section of the shock wave collapsed toward the stellar explosion, or supernova, in what the authors call a “reverse shock.”

Shock wave moving through the inner and outer shells of gas in Cassiopeia A.


This image shows the shock wave moving through the inner and outer shells of gas in Cassiopeia A. These blue arrows show the western part of the nebula’s shell moving back toward the center. Images courtesy of

This nebula, or gas cloud, is one of the closest supernova remnants to Earth, left by a supernova in the constellation Cassiopeia.

Approximately 16 light-years wide, the nebula is made of gas that was expelled both during and before the explosion that ripped apart the original star.

In theory, this shock wave should expand evenly, like a perfectly round balloon that’s continuously inflated by the shock wave from the explosion.

Image of Cassiopeia A as viewed by NASA's Imaging X-ray Polarimetry Explorer.


Cassiopeia A as viewed by NASA’s Imaging X-ray Polarimetry Explorer (magenta) and NASA’s Chandra X-Ray Observatory (blue). Image by NASACXCSAOIXPE

According to theoretical supernova models, Cassiopeia A’s western region has an unusual expansion. In the aftermath of the stellar explosion, something strange happened to the shock wave..

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