Webb reveals never-before-seen details on Cassiopeia A

(Nanowerk News) The explosion of a star is a dramatic event, but the remnants of a star left behind can be even more dramatic. A new mid-infrared image from NASA’s James Webb Space Telescope provides one stunning example. It shows the remnant of the supernova Cassiopeia A (Cas A), which was created in the explosion of a star 340 years ago. Cas A is the youngest known remnant of a massive, exploding star in our galaxy, which makes it a unique opportunity to learn more about how such a supernova occurs.

“Cas A represents our best chance to look at debris fields of exploding stars and to run some sort of stellar autopsy to understand what kind of star existed before and how it exploded,” said Danny Milisavljevic of Purdue University in West Lafayette. Indiana, the lead investigator of the Webb program that captured this observation.

“Compared to previous infrared images, we saw incredible detail that we had never had access to before,” added Tea Temim of Princeton University in Princeton, New Jersey, one of the program’s researchers.

Cassiopeia A is a prototypical supernova remnant that has been studied extensively by a number of ground-based and space-based observatories, including NASA’s Chandra X-ray Observatory. Multi-wavelength observations can be combined to give scientists a more comprehensive understanding of the remains. Cassiopeia A (Cas A) is a supernova remnant located about 11,000 light years from Earth in the constellation Cassiopeia. It covers about 10 light years. This new image uses data from Webb’s Mid-Infrared Instrument (MIRI) to reveal Cas A in a new light. On the outer remains, especially at the top and to the left, were curtains of a material that looked orange and red from the warm glow of the dust. This marks where material ejected from the exploding star hits material around the star. On the inside of this outer shell are mottled filaments of bright pink color inlaid with clumps and knots. It represents matter from the star itself, and most likely glows due to a mixture of heavy elements and dust emission. Stellar material can also be seen as dim lumps near the interior of the cavity. The circle represented in green extends across the right side of the center cavity. Their shape and complexity are unexpected and challenging for scientists to understand. This image incorporates various filters with red set to 25.5 micron (F2550W), orange-red to 21 micron (F2100W), orange to 18 micron (F1800W), yellow to 12.8 micron (F1280W), green to 11, 3 micron (F1130W) , cyan to 10 micron (F1000W), light blue to 7.7 micron (F770W), and blue to 5.6 micron (F560W). Data is from the 1947 general observer program. (Images: NASA, ESA, CSA, Danny Milisavljevic (Purdue University), Teh Temim (Princeton University), Ilse De Looze (UGent))

Dissecting Images

The striking colors of the new Cas A image, where infrared light is translated into visible light wavelengths, hold a wealth of scientific information that the team is only just beginning to unearth. On the outside of the bubble, especially on the top and left, are curtains of a material that looks orange and red from the warm glow of dust. This marks where material ejected from the exploding star hits the gas and dust around the star.

On the inside of this outer shell are mottled filaments of bright pink color inlaid with clumps and knots. This is the material of the star itself, which glows due to a mixture of heavy elements, such as oxygen, argon, and neon, as well as the emission of dust.

“We are still trying to disentangle all these sources of emissions,” said Ilse De Looze of the University of Ghent in Belgium, another research associate on the program.

Stellar material can also be seen as dim lumps near the interior of the cavity.

Perhaps most prominently, the circle represented in green runs along the right side of the center cavity. “We named it the Green Monster in honor of Fenway Park in Boston. If you look closely, you will see that it is pockmarked with mini bubbles,” said Milisavljevic. “Their form and complexity are unfathomable and challenging to comprehend.”

The Origin of Cosmic Dust – and Us

Among the science questions Cas A might help with is: Where does cosmic dust come from? Observations have found that even the very young galaxies in the early universe were covered with large amounts of dust. It’s hard to explain the origin of this dust without triggering a supernova, which spews large amounts of heavy elements (the building blocks of dust) across space.

However, existing supernova observations cannot explain with certainty the amount of dust we see in these early galaxies. By studying Cas A with Webb, astronomers hope to gain a better understanding of its dust content, which could help inform our understanding of where the building blocks of planets and ourselves were created.

“In Cas A, we can spatially resolve areas that have different gas compositions and see what types of dust are formed in those areas,” explained Temim.

Supernovas like the one that forms Cas A are essential to 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 a new generation of stars and planets.

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

The remnants of Cas A span about 10 light years and are located 11,000 light years away in the constellation Cassiopeia.