NASA has released a new image of supernova remnant Cassiopeia A (Cas A) taken by the James Webb Space Telescope (JWST). JWST used its Near-Infrared Camera (NIRCam) to image Cas A in a different way, despite it being among the most well-studied supernova remnants in the cosmos.
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Cas A is about 11,000 light-years away from Earth in the constellation Cassiopeia. It is made from the remains of gigantic star that astronomers believe exploded about 340 years ago. Since then, NASA’s Chandra X-Ray Observatory, the Hubble Space Telescope, and now retired Spitzer Space Telescope assembled a multiwavelength picture of the remains of the stellar explosion. JWST enabled astronomers to observe Cas A at different wavelengths. The image shows the more intricate details of this expanding shell of material slamming into the gas that was shed by the star before it exploded.
Color coding
In April, an image of Cas A created with JWST’s Mid-Infrared Instrument revealed some new and surprising features in its inner shell. Astronomers are now looking into why many of these features are also present in the new image taken with NIRCam, which offers a different view of the same supernova remnants.
To the human eye, infrared light is invisible. Image processors and scientists translate these wavelengths of light into visible colors for images like this one. Colors were assigned to various filters from JWST’s NIRCam which sees in near-infrared light. Each hue hints at something different happening within Cas A.
The clumps of bright orange and light pink make up the inner shell of the supernova remnant. JWST detected tiny knots of gas made up of sulfur, oxygen, argon, and neon that originated from the now exploded star itself. A mixture of dust and molecules that should one day become the components of new stars and planetary systems are embedded within the gas.
“With NIRCam’s resolution, we can now see how the dying star absolutely shattered when it exploded, leaving filaments akin to tiny shards of glass behind,” Purdue University astronomer Danny Milisavljevic said in a statement. “It’s really unbelievable after all these years studying Cas A to now resolve those details, which are providing us with transformational insight into how this star exploded.”
In the new near-infrared view, Cas A’s inner cavity and outermost shell are less colorful when compared with the mid-infrared view JWST previously took. A region which looked deep orange and red when imaged by MIRI now appears more white like smoke. This shows where the initial star explosion’s blast wave is colliding into surrounding circumstellar material. The dust is too cool to be detected directly at near-infrared wavelengths, but lights up in the mid-infrared.
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The team believes that the smoke-like sections of the image are from synchrotron radiation. This kind of light is emitted across the electromagnetic spectrum, including the near-infrared. Synchrotron radiation is generated by charged particles that are hurtling through space at very high speeds and spiraling around magnetic field lines.
A missing ‘Green Monster’ and a new ‘baby’
A loop of green light in the central cavity nicknamed the Green Monster is also not seen in this new image. When it was first spotted, researchers described it as “challenging to understand.” While it is invisible in the NIRCam image, the circular holes that were just visible in the previous MIRI image are faintly outlined in white and purple in this new NIRCam image. The white and purple represent ionized gas. The team believes that the ionized gas is caused by the supernova debris pushing through and sculpting the gas left behind by the star before it exploded.
While the Green Monster may have been missing from NIRCam’s image, the team was in for a different surprise. A large blob was visible at the bottom right corner of NIRCam’s field of view. This giant blob is called Baby Cas A since it looks like offspring of the main supernova remnant.
Baby Cas A is a light echo, where light from the long-ago stellar explosion is warming distant dust. This far away dust is glowing as it cools down. The team is particularly intrigued by Baby Cas A’s intricate dust pattern and its proximity to Cas A itself. Baby Cas A is likely located about 170 light-years behind the supernova remnant.
