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A beautiful new view of the supernova remnant of Cassiopeia A

Cassiopeia A is one of the most examined supernova remnants. Over the years, various telescopes have observed and photographed it in diverse wavelength ranges to assist scientists recount its narrative. Recently, the James Webb telescope also had the occasion to examine it and capture it in a vibrant near-infrared image acquired employing the NIRCam camera. The image attained with the instruments exhibits the remnants of a very robust explosion with a resolution antecedently unattainable at these wavelengths.

This image, which differs from the MIRI mid-infrared image taken in April this year, unveils the intricate details of the expanding shell of the material. This shell was ejected by the explosion of the star 340 years ago and is now gradually colliding into the gas ejected by the star before the explosion. MIRI and NIRCam, in particular, have identified new and unexpected features inside the shell that are paramount for examining supernova remnants.

In this recent image of Cassiopeia A, the colors have been assigned by various NIRCam filters, and each of them indicates a distinct activity transpiring inside the object. Webb's extremely sharp vision was capable to detect tiny clumps of gas consisting of sulfur, oxygen, argon and neon emanating from the star itself. This gas contains a mixture that will eventually constitute part of new stars and planetary systems.

Some of the strands of debris are too small to be resolved even with Webb, which denotes that they are comparable to or less than 16 billion kilometers. For comparison, the entire Cassiopeia A stretches for 10 light-years. In the lower right corner of the NIRCam field of view is a substantial striped mass dubbed "Baby Cas A", which materializes to be a descendant of the main supernova. This is an echo of the light from the explosion of the star, which reached and heated the distant dust, glowing when cooled. Baby Cas A is situated about 170 light-years behind the supernova remnant.

Comparing the new image of Cassiopeia A in the near infrared range with the image of MIRI in the middle infrared range, it can be discerned that the inner cavity and outer shell have a strange colorless appearance. The periphery of the main inner shell, which was orange-red in the MIRI image, now resembles smoke. This area marks the site where the supernova shock wave strikes the surrounding circumstellar matter. The dust in the circumstellar matter is too cold to be detected directly in the near-infrared region.

The academicians explain that the white color is synchrotron radiation, which is emitted by charged particles moving at extremely high speeds. Synchrotron radiation is also visible in the bubble-like shells in the lower half of the inner cavity. Although the "Green Monster" is not visible in the NIRCam image, what remains in the near-infrared range may provide information about the mysterious feature. The round holes faintly outlined represent ionized gas, likely due to the supernova debris pushed through the gas left after the explosion.

As next-gen telescopes akin to Webb apply their enhanced optics and infrared imaging capabilities to examine astronomical phenomena like supernova remnants, novel revelations about these objects will likely emerge. The comparison of Cassiopeia A images across wavelength ranges already demonstrates Webb's competency to unveil previous unseen structural intricacies. Such validating early science results bode well for the observatory's capacity to push the frontiers of high-redshift astronomy in the imminent future.

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