New research suggests that the Green Monster — a curious structure first spotted in Webb data in April 2023 — came from that blast wave slamming into material surrounding the Cassiopeia A supernova remnant.
Cassiopeia A is located about 11,000 light-years away from Earth in the constellation of Cassiopeia.
Also known as Cas A, SNR G111.7-02.1 or NRAO 711, the object spans approximately 10 light-years.
When the original star ran out of fuel, it collapsed onto itself and blew up as a supernova, possibly briefly becoming one of the brightest objects in the sky.
Although astronomers think that this happened around the year 1680, there are no verifiable historical records to confirm this.
A curious structure dubbed the Green Monster was first identified in infrared data from the NASA/ESA/CSA James Webb Space Telescope in April 2023, but its origin was not clear.
However, by combining the Webb data with X-rays from NASA’s Chandra X-ray Observatory, astronomers think they have hunted down the source of this feature.
“We already suspected the Green Monster was created by a blast wave from the exploded star slamming into material surrounding it. Chandra helped us clinch the case,” said Dr. Jacco Vink, an astronomer at the University of Amsterdam.
When a massive star exploded to create Cassiopeia A about 340 years ago, from Earth’s perspective, it created a ball of matter and light that expanded outward. In the outer parts of Cassiopeia A the blast wave is striking surrounding gas that was ejected by the star between about 10,000 and 100,000 years before the explosion.
That formed a favorable environment for dust formation after the ejected stellar material cooled down.
The Chandra data reveal hot gas, mostly from supernova debris including elements like silicon and iron, but also from energetic electrons spiraling around magnetic field lines in the blast wave.
These electrons light up as thin arcs near the blast wave, and also show up in parts of the…
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