New near-infrared observations from the Webb telescope reveal intricate strands of debris from the exploded star.
This new infrared image from the James Webb Space Telescope reveals the intricate knots of debris inside the supernova remnant Cassiopeia A. Cas A lies about 11,000 light-years from Earth and formed more than 300 years ago when a massive star went kablooey.
Spectroscopic study of the explosion’s light echo — the reflection of the flash off surrounding dust grains — has previously revealed that the event was a Type IIb supernova, the death of a big star stripped of most of its hydrogen shell.
JWST astronomers released a different image of Cas A earlier this year (see below). That one was assembled from mid-infrared data and highlighted in reddish orange where the expanding blast wave is ramming into material surrounding the dead star. In the new image, the outer regions have instead been colored white. This is not merely an aesthetic choice but one made to highlight that we’re looking at different kinds of emission: In mid-infrared, we were detecting glowing dust; in the near-infrared image, we’re seeing emission from electrons corkscrewing along magnetic field lines at breakneck speeds.
The most eye-catching part of the first, near-infrared image is the pinkish festoons. These strands are debris from the now-dead star and comprise sulfur, oxygen, argon, and neon. Dust sprinkles the mix. Cas A spans some 10 light-years, but some of these ejecta filaments are so small that they evade JWST’s resolution at this distance, meaning they’re at most 100 astronomical units across — roughly twice the size of the solar system, if you include the main part of the Kuiper Belt outside Neptune’s orbit.
Dust is a major player in stellar evolution. It helps cool gas, enabling it to collapse and form stars. Astronomers still question what the universe’s primary source of dust is. Some dust comes from aging, puffy giants that are sloughing off their outer layers as winds, but these don’t form rapidly enough to explain the high quantities of dust found in the early universe.
Supernovae also create dust, which forms in the cooling ejecta. The problem is, supernovae destroy the same dust they create: The shock wave created when the ejecta slam into surrounding material rebounds back into the remnant’s interior, heating and destroying dust as it goes.
The highly clumpy nature of ejecta that JWST is revealing could explain how dust survive this process: Grains may shelter deep inside the clumps, away from the shock wave’s destructive effects.
We’ll talk more about Cas A and other supernova remnants in our May 2024 issue. Subscribe now!
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