Astronomers reveal the secret of one of the most famous explosions in our galaxy

(ORDO NEWS) — A new analysis of one of the most famous explosions in space has revealed a curious asymmetry.

Part of the inner nebula Cassiopeia A is not a supernova remnant, as astronomers have discovered, but is expanding evenly.

Something caused part of the cloud to move not outward along with the rest of the material, but inward, back toward the source of the explosion: a reverse thrust.

Cassiopeia A, located at a distance of 11,000 light years, is one of the most famous and well-studied objects in the Milky Way. This is what we call a supernova remnant – an expanding cloud of ejecta left over from the explosion of a massive star.

Supernova Cassiopeia A is believed to have been first observed in the 1670s, and astronomers have been studying its remnants ever since. This is an excellent sample for studying the evolution of supernovae.

Cassiopeia A emits light at multiple wavelengths and consists of a large, roughly spherical shell of expanding material that was likely ejected prior to the supernova explosion as the star became increasingly unstable.

Astronomers reveal the secret of one of the most famous explosions in our galaxy 2

This material is expanding at an average speed of somewhere between 4,000 and 6,000 kilometers per second.

In their new study, Wink and colleagues looked at 19 years of Chandra X-ray data to piece together how the remnant has changed over time.

They found that the patch on the western side of the inner region of the shell bounces inward toward the center at 3,000 to 8,000 kilometers per second.

They also found that the external shock wave of the same section of the shell accelerates. According to computer models of an expanding shock wave, a collision with something will first cause the shock wave front to slow down and then speed up.

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So what could the shock wave have encountered?

We know from other supernova remnants that matter in the space around a star can backfire; denser regions of interstellar gas and dust, for example, or even the previous slower-moving sheath of material ejected by the star in its death throes.

In the case of Cassiopeia A, a dense region of material emitted by a dying star may have formed a partial shell into which the remnant crashed, expanding outward.

It could also be the result of a brief phase of extreme Wolf-Rayet mass loss experienced by really huge stars that created a cavity in space around the star.

In fact, we don’t know much about the progenitor star that created the supernova remnant Cassiopeia A. We don’t know how big it was, how old it was, or what its spectral type is. These results, the researchers say, may provide some clues.

It is amazing that new details are still being discovered in an object as well studied as Cassiopeia A. With new instruments turning their eyes on the object, we can only expect more mysteries to be uncovered in the coming years.

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