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NASA’s Webb Stuns With New High-Definition Look at Exploded Star

Cassiopeia A, a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments studded with clumps and knots that look like tiny pieces of shattered glass. Around the exterior of the inner shell, particularly at the upper right, there are curtains of wispy gas that look like campfire smoke. The white smoke-like material also appears to fill the cavity of the inner shell, featuring structures shaped like large bubbles. Around and within the nebula, there are various stars seen as points of blue and white light. Outside the nebula, there are also clumps of yellow dust, with a particularly large clump at the bottom right corner that appears to have very detailed striations.
A new high-definition image from NASA’s 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...
Credits: Image: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGhent), Tea Temim (Princeton University)
The headshot image of NASA Webb Mission Team

NASA Webb Mission Team

Goddard Space Flight Center

Dec 10, 2023
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Mysterious features hide in near-infrared light

Like a shiny, round ornament ready to be placed in the perfect spot on a holiday tree, supernova remnant Cassiopeia A (Cas A) gleams in a new image from NASA’s James Webb Space Telescope. As part of the 2023 Holidays at the White House, First Lady of the United States Dr. Jill Biden debuted the first-ever White House Advent Calendar. To showcase the “Magic, Wonder, and Joy” of the holiday season, Dr. Biden and NASA are celebrating with this new image from Webb.

While all is bright, this scene is no proverbial silent night. Webb’s NIRCam (Near-Infrared Camera) view of Cas A displays this stellar explosion at a resolution previously unreachable at these wavelengths. This high-resolution look unveils intricate details of the expanding shell of material slamming into the gas shed by the star before it exploded.

Cas A is one of the most well-studied supernova remnants in all of the cosmos. Over the years, ground-based and space-based observatories, including NASA’s Chandra X-Ray Observatory, Hubble Space Telescope, and retired Spitzer Space Telescope have assembled a multiwavelength picture of the object’s remnant.

However, astronomers have now entered a new era in the study of Cas A. In April 2023, Webb’s MIRI (Mid-Infrared Instrument) started this chapter, revealing new and unexpected features within the inner shell of the supernova remnant. Many of those features are invisible in the new NIRCam image, and astronomers are investigating why.

Image: Cassiopeia A (NIRCam)

Cassiopeia A, a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments studded with clumps and knots that look like tiny pieces of shattered glass. Around the exterior of the inner shell, particularly at the upper right, there are curtains of wispy gas that look like campfire smoke. The white smoke-like material also appears to fill the cavity of the inner shell, featuring structures shaped like large bubbles. Around and within the nebula, there are various stars seen as points of blue and white light. Outside the nebula, there are also clumps of yellow dust, with a particularly large clump at the bottom right corner that appears to have very detailed striations.
A new high-definition image from NASA’s 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...
Image: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGhent), Tea Temim (Princeton University)

‘Like Shards of Glass’

Infrared light is invisible to our eyes, so image processors and scientists translate these wavelengths of light to visible colors. In this newest image of Cas A, colors were assigned to different filters from NIRCam, and each of those colors hints at different activity occurring within the object.

At first glance, the NIRCam image may appear less colorful than the MIRI image. However, this simply comes down to the wavelengths in which the material from the object is emitting its light.

The most noticeable colors in Webb’s newest image are clumps represented in bright orange and light pink that make up the inner shell of the supernova remnant. Webb’s razor-sharp view can detect the tiniest knots of gas, comprised of sulfur, oxygen, argon, and neon from the star itself. Embedded in this gas is a mixture of dust and molecules, which will eventually become components of new stars and planetary systems. Some filaments of debris are too tiny to be resolved by even Webb, meaning they are comparable to or less than 10 billion miles across (around 100 astronomical units). In comparison, the entirety of Cas A spans 10 light-years across, or 60 trillion miles.

“With NIRCam’s resolution, we can now see how the dying star absolutely shattered when it exploded, leaving filaments akin to tiny shards of glass behind,” said Danny Milisavljevic of Purdue University, who leads the research team. “It’s really unbelievable after all these years studying Cas A to now resolve those details, which are providing us with transformational insight into how this star exploded.”

Image: Cassiopeia A NIRCam/MIRI

A comparison between two images, one on the left (labeled NIRCam), and on the right (labeled MIRI), separated by a white line. Both are a square image rotated clockwise about 45 degrees, with solid black in the top left, top right, bottom left, and bottom right corners. On the left, the image is a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments that look like tiny pieces of shattered glass. Around the exterior of the inner shell are curtains of wispy gas that look like campfire smoke. The white smoke-like material also fills the cavity of the inner shell, with structures shaped like large bubbles. Outside the nebula, there are also clumps of yellow dust. On the right, is the same nebula in different light. The curtains of material outside the inner shell glow orange instead of white. The inner shell looks more mottled, and is a muted pink. At center right, a greenish loop extends from the right side of the ring into the central cavity.
This image provides a side-by-side comparison of supernova remnant Cassiopeia A (Cas A) as captured by NASA’s James Webb Space Telescope’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument). At first glance, Webb’s NIRCam image appears less colorful than the MIRI...
Image: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGhent), Tea Temim (Princeton University)

Hidden Green Monster

When comparing Webb’s new near-infrared view of Cas A with the mid-infrared view, its inner cavity and outermost shell are curiously devoid of color.

The outskirts of the main inner shell, which appeared as a deep orange and red in the MIRI image, now look like smoke from a campfire. 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.

Researchers say the white color is light from synchrotron radiation, which is emitted across the electromagnetic spectrum, including the near-infrared. It’s generated by charged particles traveling at extremely high speeds spiraling around magnetic field lines. Synchrotron radiation is also visible in the bubble-like shells in the lower half of the inner cavity.

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, nicknamed the Green Monster by the research team. This feature was described as “challenging to understand” by researchers at the time of their first look.

While the ‘green’ of the Green Monster is not visible in NIRCam, what’s left over in the near-infrared in that region can provide insight into the mysterious feature. The circular holes visible in the MIRI image are faintly outlined in white and purple emission in the NIRCam image – this represents ionized gas. Researchers believe this is due to the supernova debris pushing through and sculpting gas left behind by the star before it exploded.

Image: Cassiopeia A Features

The image is split into 5 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, labeled 1, 2, 3, and 4. The 4 images in the column are zoomed-in areas of the larger square image on the left. The image on the left has a circular-shaped cloud of gas and dust with 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 labeled 1. Around the exterior of the inner shell in the main image there are wispy curtains of gas that look like campfire smoke. Within the cavity of the inner shell, there are small circular bubbles outlined in white. Box 2 is a zoom-in on these circles. Scattered outside the nebula in the main image, there are also clumps of yellow dust. 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.
This image highlights several interesting features of supernova remnant Cassiopeia A as seen with Webb’s NIRCam (Near-Infrared Camera): NIRCam’s exquisite resolution is able to detect tiny knots of gas, comprised of sulfur, oxygen, argon, and neon from the star itself. Some...
Image: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGhent), Tea Temim (Princeton University)

Related Information

Lifecycle of Stars

More Webb News - https://science.nasa.gov/mission/webb/latestnews/

More Webb Images - https://science.nasa.gov/mission/webb/multimedia/images/

Webb Mission Page - https://science.nasa.gov/mission/webb/

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Related Images & Videos

Cassiopeia A, a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments studded with clumps and knots that look like tiny pieces of shattered glass. Around the exterior of the inner shell, particularly at the upper right, there are curtains of wispy gas that look like campfire smoke. The white smoke-like material also appears to fill the cavity of the inner shell, featuring structures shaped like large bubbles. Around and within the nebula, there are various stars seen as points of blue and white light. Outside the nebula, there are also clumps of yellow dust, with a particularly large clump at the bottom right corner that appears to have very detailed striations.

Cassiopeia A (NIRCam Image)

A new high-definition image from NASA’s 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...

The image is split into 5 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, labeled 1, 2, 3, and 4. The 4 images in the column are zoomed-in areas of the larger square image on the left. The image on the left has a circular-shaped cloud of gas and dust with 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 labeled 1. Around the exterior of the inner shell in the main image there are wispy curtains of gas that look like campfire smoke. Within the cavity of the inner shell, there are small circular bubbles outlined in white. Box 2 is a zoom-in on these circles. Scattered outside the nebula in the main image, there are also clumps of yellow dust. 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.

Cassiopeia A Close-ups (NIRCam Image)

This image highlights several interesting features of supernova remnant Cassiopeia A as seen with Webb’s NIRCam (Near-Infrared Camera): NIRCam’s exquisite resolution is able to detect tiny knots of gas, comprised of sulfur, oxygen, argon, and neon from the star itself. Some...

A comparison between two images, one on the left (labeled NIRCam), and on the right (labeled MIRI), separated by a white line. Both are a square image rotated clockwise about 45 degrees, with solid black in the top left, top right, bottom left, and bottom right corners. On the left, the image is a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments that look like tiny pieces of shattered glass. Around the exterior of the inner shell are curtains of wispy gas that look like campfire smoke. The white smoke-like material also fills the cavity of the inner shell, with structures shaped like large bubbles. Outside the nebula, there are also clumps of yellow dust. On the right, is the same nebula in different light. The curtains of material outside the inner shell glow orange instead of white. The inner shell looks more mottled, and is a muted pink. At center right, a greenish loop extends from the right side of the ring into the central cavity.

Cassiopeia A (NIRCam and MIRI side by side)

This image provides a side-by-side comparison of supernova remnant Cassiopeia A (Cas A) as captured by NASA’s James Webb Space Telescope’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument). At first glance, Webb’s NIRCam image appears less colorful than the MIRI...

An image labeled “James Webb Space Telescope, Cassiopeia A, SNR G111.7-02.1.” The image has a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments that look like tiny pieces of shattered glass. Around the exterior of the inner shell there are curtains of wispy gas that look like campfire smoke. The white smoke-like material also appears to fill the cavity of the inner shell, featuring structures shaped like large bubbles. Around and within the nebula, there are various stars seen as points of blue and white light. Outside the nebula, there are also clumps of yellow dust. At lower left, a white arrow pointing in the 2 o’clock direction is labeled N for north, while an arrow pointing in the 10 o‘clock direction is labeled E for east. At lower right, a scale bar is labeled 3 light-years and 1 arcminute. At the bottom is a list of MIRI filters in different colors, from left to right: F162M (blue), F356W (green), and F444W (red).

Cassiopeia A (NIRCam Compass Image)

This image of the Cassiopeia A supernova remnant, captured by Webb’s NIRCam (Near-Infrared Camera) shows compass arrows, scale bar, and color key for reference. The north and east compass arrows show the orientation of the image on the sky. The scale bar is labeled in...

Cassiopeia A, a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments studded with clumps and knots that look like tiny pieces of shattered glass. Around the exterior of the inner shell, particularly at the upper right, there are curtains of wispy gas that look like campfire smoke. The white smoke-like material also appears to fill the cavity of the inner shell, featuring structures shaped like large bubbles. Around and within the nebula, there are various stars seen as points of blue and white light.

Take a Tour of Cassiopeia A

This video tours Webb’s NIRCam (Near-Infrared Camera) image of supernova remnant Cassiopeia A (Cas A). NIRCam’s high resolution detects tiny knots of gas leftover from the star’s explosion, as well as light echoes scattered across the field of view.

Telescope image including distant stars is overlaid with a semi-transparent graphic representing the constellation Cassiopeia, the queen. Thin blue lines in the outline of a “W” connect the actual stars of the constellation.

Cassiopeia A Zoom

This zoom-in video shows the relative location of supernova remnant Cassiopeia A (Cas A) on the sky. It begins with a ground-based photo by the late astrophotographer Akira Fujii. As it zooms into smaller portions of the sky, it fades into an image from the Digital Sky Survey....

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Last Updated
Aug 28, 2025
Location
NASA Goddard Space Flight Center
Contact
Media

Laura Betz
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
laura.e.betz@nasa.gov

Hannah Braun
Space Telescope Science Institute
Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute
Baltimore, Maryland

Science Credit

Danny Milisavljevic (Purdue University), Ilse De Looze (UGhent), Tea Temim (Princeton University)

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