One of the most famous explosions in our galaxy could collide with something

(ORDO NEWS) — A new analysis of one of the most famous explosions in space has revealed a curious asymmetry. Part of the inner nebula of supernova remnant Cassiopeia A, as astronomers have found, is expanding unevenly.

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 backlash.

“The reversal in the west could mean two things,” says astronomer Jakko Wink of the University of Amsterdam in the Netherlands.

“Either there’s a hole somewhere in the supernova’s material, a kind of vacuum, causing the hot envelope to suddenly move inwards locally. Or the nebula has collided with something.”

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 the so-called supernova remnant – an expanding cloud of emissions left after the explosion of a massive star.

Supernova Cassiopeia A is believed to have been first seen in the 1670s, illuminating the sky, and astronomers have been studying its remnant ever since. This is an excellent example for studying the evolution of supernovae.

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

This material is expanding at an average speed of 4,000 to 6,000 kilometers (2,485 to 3,730 miles) per second.

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

They found that the area on the western side of the inner region of the shell bounces inward towards the center at a speed of 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 first slows down and then accelerates the shock wave front: “Exactly the way we measured it,” Vink explains.

One of the most famous explosions in our galaxy could collide with something 2

What could be the impact of the shock wave?

We know from other supernova remnants that material in space around a star can create backs hocks; for example, denser regions of interstellar gas and dust, or even a previous, slower moving shell of material ejected by a star during its death throes.

In the case of Cassiopeia A, the dense region of material ejected by the dying star could have formed a partial shell for the remnant that it crashed into while expanding outward.

It could also be the result of a short Wolf-Ryet phase, the extreme mass loss that really huge stars experience, resulting in a cavity in the space around the star.

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

“The shock wave dynamics reported here provide important clues about the late history of progenitor mass loss, whether in the form of a partial, asymmetric sheath from episodic mass loss, an aspherical cavity created by the transient wind of the Wolf-Rayet phase, or perhaps even a combination both,” they write in their article.

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


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