James Webb Space Telescope Discovery

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Date: 12/11/2023

Cassiopeia A (NIRCam Image)

A new high-definition image from the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) unveils intricate details of supernova remnant Cassiopeia A (Cas A), and shows the expanding shell of material slamming into the gas shed by the star before it exploded. The most noticeable colours in Webb’s newest image are clumps of bright orange and light pink that make up the inner shell of the supernova remnant. These tiny knots of gas, composed of sulphur, oxygen, argon, and neon from the star itself, are only detectable thanks to NIRCam’s exquisite resolution, and give researchers a hint at how the dying star shattered like glass when it exploded. The outskirts of the main inner shell look like smoke from a campfire. This marks where ejected material from the exploded star is ramming into surrounding circumstellar material. Researchers have concluded that this white colour is light from synchrotron radiation, which is generated by charged particles travelling at extremely high speeds and spiralling around magnetic field lines. There are also several light echoes visible in this image, most notably in the bottom right corner. This is where light from the star’s long-ago explosion has reached, and is warming, distant dust, which glows as it cools down. In April 2023, Webb’s MIRI (Mid-Infrared Instrument) started this story, revealing new and unexpected features within the inner shell of the supernova remnant. But many of those features are invisible in the new NIRCam image, and astronomers are investigating why that is. Credit: NASA, ESA, CSA, STScI, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (University of Gent) Cas A (NIRCam image) 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. Cas A (NIRCam image, annotated) This image provides a side-by-side comparison of supernova remnant Cassiopeia A (Cas A) as captured by the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument). At first glance, Webb’s NIRCam image appears less colourful than the MIRI image. But this is only because the material from the object is emitting light at many different wavelengths The NIRCam image appears a bit sharper than the MIRI image because of its greater resolution. The outskirts of the main inner shell, which appeared as a deep orange and red in the MIRI image, look like smoke from a campfire in the NIRCam image. This marks where the supernova blast wave is ramming into surrounding circumstellar material. The dust in the circumstellar material is too cool to be detected directly at near-infrared wavelengths, but lights up in the mid-infrared. Also not seen in the near-infrared view is the loop of green light in the central cavity of Cas A that glowed in mid-infrared light, nicknamed the Green Monster by the research team. The circular holes visible in the MIRI image within the Green Monster, however, are faintly outlined in white and purple emission in the NIRCam image. Cas A (NIRCam and MIRI Comparison) Cas A (NIRCam compass image) Cas A (NIRCam image, scaled) Cas A (MIRI image, scaled) Raw images Cas A MIRI discovery page