New Webb image reveals Cas A supernova remnant

A new mid-infrared image from NASA’s James Webb Space Telescope has revealed new details from the aftermath of a supernova seen from Earth 340 years ago.

NASA, ESA, CSA, D. D. Milisavljevic (Purdue), T. Temim (Princeton), I. De Looze (Ghent University). Image Processing: J. DePasquale (STScI)

Cassiopeia A (Cas A) is the youngest known remnant from a massive exploding star in our galaxy. Located 11,000 light-years away in the constellation Cassiopeia, it spans about 10 light-years. According to NASA, it is a prototypical supernova remnant and has been widely studied by a number of ground-based and space-based observatories, including the space agency’s own Chandra X-ray Observatory.

Webb captured the data from Cas A using the telescope’s mid-infrared instrument (MIRI), with NASA later converting the infrared into visible light in order to to create the impressively detailed image. Historical multi-wavelength observations can be combined with the new data to provide scientists with a more comprehensive understanding of the remnant, according to the NASA team.

“Cas A represents our best opportunity to look at the debris field of an exploded star and run a kind of stellar autopsy to understand what type of star was there beforehand and how that star exploded,” said Danny Milisavljevic of Purdue University in West Lafayette, Indiana, principal investigator of the Webb programme that captured the observations.

The colours within the new image hold a wealth of scientific information that the team is just beginning to explore. On the bubble’s exterior, particularly at the top and left, lie curtains of material appearing orange and red due to emission from warm dust. This marks where ejected material from the exploded star is ramming into surrounding circumstellar gas and dust.

Interior to this outer shell are mottled filaments of bright pink studded with clumps and knots. This represents material from the star itself, which is shining due to a mix of various heavy elements, such as oxygen, argon, and neon, as well as dust emission.

“We’re still trying to disentangle all these sources of emission,” said Ilse De Looze of Ghent University in Belgium, another co-investigator on the programme.

Perhaps most prominently, a loop represented in green extends across the right side of the central cavity.

“We’ve nicknamed it the Green Monster in honour of Fenway Park in Boston,” said Milisavljevic. “If you look closely, you’ll notice that it’s pockmarked with what look like mini bubbles. The shape and complexity are unexpected and challenging to understand.”

Supernovae like the one that formed Cas A are crucial for life as we know it. They spread elements like the calcium we find in our bones and the iron in our blood across interstellar space, seeding new generations of stars and planets.

“By understanding the process of exploding stars, we’re reading our own origin story,” said Milisavljevic. “I’m going to spend the rest of my career trying to understand what’s in this data set.”