Cas A (NIRCam image, annotated)

This image highlights several interesting features of the supernova remnant Cassiopeia A (Cas A), as seen with Webb’s NIRCam (Near-Infrared Camera).

NIRCam’s exquisite resolution is able to detect tiny knots of gas, composed of sulphur, oxygen, argon, and neon from the star itself. Some filaments of debris are too tiny to be resolved, even by Webb, meaning that they are comparable to or less than 16 billion kilometres across (around 100 astronomical units). Researchers consider that this represents how the star shattered like glass when it exploded.

Circular holes visible in the MIRI image within the Green Monster, a loop of green light in Cas A’s inner cavity, are faintly outlined in white and purple emission in the NIRCam image — this represents ionised gas. Researchers believe this is due to the supernova debris pushing through and sculpting gas left behind by the star before it exploded.

This is one of a few light echoes visible in NIRCam’s image of Cas A. A light echo occurs when light from the star’s long-ago explosion has reached, and is warming, distant dust, which glows as it cools down.

NIRCam captured a particularly intricate and large light echo, nicknamed Baby Cas A by researchers. It is actually located about 170 light-years behind the supernova remnant.

[Image description: The image is split into five boxes. A large image at the left-hand side takes up most of the image. There are four images along the right-hand side in a column, which show zoomed-in areas of the larger square image on the left. The image on the left shows a roughly circular cloud of gas and dust with a complex structure, with an inner shell of bright pink and orange filaments that look like tiny pieces of shattered glass. A zoom-in of this material appears in the box labelled 1. Around the exterior of the inner shell in the main image there are wispy curtains of gas that look like campfire smoke. Box 2 is a zoom-in on these circles. Scattered outside the nebula in the main image are clumps of dust, coloured yellow in the image. Boxes 3 and 4 are zoomed-in areas of these clumps. Box 4 highlights a particularly large clump at the bottom right of the main image that is detailed and striated.]