Webb, Chandra, Hubble, and Spitzer Together Explore Cassiopeia A

For the first time astronomers have combined data from NASA’s Chandra X-ray Observatory and James Webb Space Telescope to study the well-known supernova remnant Cassiopeia A (Cas A). This work has helped explain an unusual structure in the debris from the destroyed star called the “Green Monster”, first discovered in Webb data in April 2023. The research has also uncovered new details about the explosion that created Cas A about 340 years ago, from Earth’s perspective.

A new composite image contains X-rays from Chandra (blue), infrared data from Webb (red, green, blue), and optical data from Hubble (red and white). The outer parts of the image also include infrared data from NASA’s Spitzer Space Telescope (red, green and blue). The outline of the Green Monster can be seen by mousing over the image in the original feature, located here: chandra.cfa.harvard.edu/photo/2024/casa/.

The Chandra data reveals hot gas, mostly from supernova debris from the destroyed star, including elements like silicon and iron. In the outer parts of Cas A the expanding blast wave is striking surrounding gas that was ejected by the star before the explosion. The X-rays are produced by energetic electrons spiraling around magnetic field lines in the blast wave. These electrons light up as thin arcs in the outer regions of Cas A, and in parts of the interior. Webb highlights infrared emission from dust that is warmed up because it is embedded in the hot gas seen by Chandra, and from much cooler supernova debris. The Hubble data shows stars in the field.

Detailed analysis by the researchers found that filaments in the outer part of Cas A, from the blast wave, closely matched the X-ray properties of the Green Monster, including less iron and silicon than in the supernova debris. This interpretation is apparent from the color Chandra image, which shows that the colors inside the Green Monster’s outline best match with the colors of the blast wave rather than the debris with iron and silicon. The authors conclude that the Green Monster was created by a blast wave from the exploded star slamming into material surrounding it, supporting earlier suggestions from the Webb data alone.

The debris from the explosion is seen by Chandra because it is heated to tens of millions of degrees by shock waves, akin to sonic booms from a supersonic plane. Webb can see some material that has not been affected by shock waves, what can be called “pristine” debris.

Read more here: chandra.cfa.harvard.edu/photo/2024/casa/.

A separate graphic of Cassiopeia A shows a color Chandra image, where red shows iron and magnesium at low X-ray energies, green shows silicon at intermediate X-ray energies and blue shows the highest energy X-rays, from electrons spiraling around magnetic field lines. An outline of the Green Monster, plus the locations of the blast wave, and of debris rich in silicon and iron are labeled.

Detailed analysis by the researchers found that filaments in the outer part of Cas A, from the blast wave, closely matched the X-ray properties of the Green Monster, including less iron and silicon than in the supernova debris. This interpretation is apparent from the color Chandra image, which shows that the colors inside the Green Monster’s outline best match with the colors of the blast wave rather than the debris with iron and silicon. The authors conclude that the Green Monster was created by a blast wave from the exploded star slamming into material surrounding it, supporting earlier suggestions from the Webb data alone.

The debris from the explosion is seen by Chandra because it is heated to tens of millions of degrees by shock waves, akin to sonic booms from a supersonic plane. Webb can see some material that has not been affected by shock waves, what can be called “pristine” debris.

To learn more about the supernova explosion, the team compared the Webb view of the pristine debris with X-ray maps of radioactive elements that were created in the supernova. They used NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) data to map radioactive titanium — still visible today — and Chandra to map where radioactive nickel was by measuring the locations of iron. Radioactive nickel decays to form iron. An additional image shows the iron-rich debris (tracing where radioactive nickel was located) in green, the radioactive titanium in blue and the pristine debris seen in orange and yellow.

Some filaments of pristine debris near the center of Cas A, seen with Webb, are connected to the iron seen with Chandra farther out. Radioactive titanium is seen where pristine debris is relatively weak.

These comparisons suggest that radioactive material seen in X-rays has helped shape the pristine debris near the center of the remnant seen with Webb, forming cavities. The fine structures in the pristine debris were most likely formed when the star’s inner layers were violently mixed with hot, radioactive matter produced during collapse of the star’s core under gravity.

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 overall, however, this is only due to the wavelengths in which the material from the object is emitting its light. The NIRCam image appears a bit sharper than the MIRI image due to its increased resolution.

The outskirts of the main inner shell, which appeared as a deep orange and red in the MIRI image, looks 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, 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.

Read more: go.nasa.gov/3NoVwBI

Cassiopeia A (Cas A) is a supernova remnant located about 11,000 light-years from Earth in the constellation Cassiopeia. It spans approximately 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 remnant’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 material.

Interior to this outer shell lie mottled filaments of bright pink studded with clumps and knots. This represents material from the star itself, and likely shines due to a mix of various heavy elements and dust emission. The stellar material can also be seen as fainter wisps near the cavity’s interior.

A loop represented in green extends across the right side of the central cavity. Its shape and complexity are unexpected and challenging for scientists to understand.

This image combines various filters with the color red assigned to 25.5 microns (F2550W), orange-red to 21 microns (F2100W), orange to 18 microns (F1800W), yellow to 12.8 microns (F1280W), green to 11.3 microns (F1130W), cyan to 10 microns (F1000W), light blue to 7.7 microns (F770W), and blue to 5.6 microns (F560W). The data comes from general observer program 1947.

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 noticeable colors 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, comprised of sulfur, oxygen, argon, and neon from the star itself, are only detectable by 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 looks like smoke from a campfire. This marks where ejected material from the exploded star is ramming into surrounding circumstellar material. Researchers say this white color is light from synchrotron radiation, which is generated by charged particles traveling at extremely high speeds spiraling 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 is glowing as it cools down.

This image highlights several interesting features of supernova remnant Cassiopeia A as seen with Webb’s NIRCam (Near-Infrared Camera):

1. NIRCam’s exquisite resolution is able to detect tiny knots of gas, comprised of sulfur, oxygen, argon, and neon from the star itself. Some filaments of debris are too tiny to be resolved even by Webb, meaning they are comparable to or less than 10 billion miles across (around 100 astronomical units). Researchers say this represents how the star shattered like glass when it exploded.

2. 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 ionized gas. Researchers believe this is due to the supernova debris pushing through and sculpting gas left behind by the star before it exploded.

3. 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 is glowing as it cools down.

4. 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.