These shimmering cosmic curtains show interstellar gas and dust that has been heated by the flashbulb explosion of a long-ago supernova. The gas then glows infrared light in what is known as a thermal light echo. As the supernova illumination travels through space at the speed of light, the echo appears to expand. The NASA/ESA/CSA James Webb Space Telescope observed this light echo in the vicinity of the supernova remnant Cassiopeia A three separate times, in essence creating a 3D scan of the interstellar material.
[Image description: Three rows show Webb images of the same region taken on three different dates. The top row is labeled August 19, 2024. The middle row is labeled September 16, 2024. The bottom row is labeled September 30, 2024. Each row shows two images split by a vertical black bar where there is no data. Each image is speckled with dozens of white stars, some showing Webb’s signature 8-point diffraction spikes, against the black background of space. The images also show tightly packed, glowing red filaments that resemble muscle fibers or wood grain. While the background stars are the same in every row, the filaments change noticeably. In the top row, the filaments extend horizontally from upper left to lower right. In the middle and bottom rows, the filaments extend from lower left to upper right, and seem to shift slightly downward in position, with the last the lowest.]