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NASA’s Webb Reveals Intricate Layers of Interstellar Dust, Gas


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NASA’s Webb Reveals Intricate Layers of Interstellar Dust, Gas

A few dozen white stars, some with Webb’s signature 8-point diffraction spikes, on the black background of space. Tightly packed, red-orange filaments extend horizontally from upper left to lower right, with a bulging upward curve on the right that is closer to the top. The filaments resemble wood grain.
This shimmering cosmic curtain shows interstellar gas and dust that has been heated by the flashbulb explosion of a long-ago supernova. The gas then glows infrared light in what is known as a thermal light echo. As the supernova illumination travels through space at the speed of light, the echo appears to expand. NASA’s James Webb Space Telescope observed this light echo in the vicinity of the supernova remnant Cassiopeia A.
Credits:
NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)

Once upon a time, the core of a massive star collapsed, creating a shockwave that blasted outward, ripping the star apart as it went. When the shockwave reached the star’s surface, it punched through, generating a brief, intense pulse of X-rays and ultraviolet light that traveled outward into the surrounding space. About 350 years later, that pulse of light has reached interstellar material, illuminating it, warming it, and causing it to glow in infrared light.

NASA’s James Webb Space Telescope has observed that infrared glow, revealing fine details resembling the knots and whorls of wood grain. These observations are allowing astronomers to map the true 3D structure of this interstellar dust and gas (known as the interstellar medium) for the first time.

“We were pretty shocked to see this level of detail,” said Jacob Jencson of Caltech/IPAC in Pasadena, principal investigator of the science program.

“We see layers like an onion,” added Josh Peek of the Space Telescope Science Institute in Baltimore, a member of the science team. “We think every dense, dusty region that we see, and most of the ones we don’t see, look like this on the inside. We just have never been able to look inside them before.”

The team is presenting their findings in a press conference at the 245th meeting of the American Astronomical Society in Washington.

“Even as a star dies, its light endures—echoing across the cosmos. It’s been an extraordinary three years since we launched NASA’s James Webb Space Telescope. Every image, every discovery, shows a portrait not only of the majesty of the universe but the power of the NASA team and the promise of international partnerships. This groundbreaking mission, NASA’s largest international space science collaboration, is a true testament to NASA’s ingenuity, teamwork, and pursuit of excellence,” said NASA Administrator Bill Nelson. “What a privilege it has been to oversee this monumental effort, shaped by the tireless dedication of thousands of scientists and engineers around the globe. This latest image beautifully captures the lasting legacy of Webb—a keyhole into the past and a mission that will inspire generations to come.”

Image A: Light Echoes Near Cassiopeia A (NIRCam)

Three rows show Webb images of the same region taken on three different dates. The top row is labeled August 19, 2024. The middle row is labeled September 16, 2024. The bottom row is labeled September 30, 2024. Each row shows two images split by a vertical black bar where there is no data. Each image is speckled with dozens of white stars, some showing Webb’s signature 8-point diffraction spikes, against the black background of space. The images also show tightly packed, glowing red filaments that resemble muscle fibers or wood grain. While the background stars are the same in every row, the filaments change noticeably. In the top row, the filaments extend horizontally from upper left to lower right. In the middle and bottom rows, the filaments extend from lower left to upper right, and seem to shift slightly downward in position, with the last the lowest.
These shimmering cosmic curtains show interstellar gas and dust that has been heated by the flashbulb explosion of a long-ago supernova. The gas then glows infrared light in what is known as a thermal light echo. As the supernova illumination travels through space at the speed of light, the echo appears to expand. NASA’s James Webb Space Telescope observed this light echo in the vicinity of the supernova remnant Cassiopeia A three separate times, in essence creating a 3D scan of the interstellar material. Note that the field of view in the top row is rotated slightly clockwise relative to the middle and bottom rows, due to the roll angle of the Webb telescope when the observations were taken.
NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)

Video A: Light Echoes Near Cassiopeia A (NIRCam)

This time-lapse video using data from NASA’s James Webb Space Telescope highlights the evolution of one light echo in the vicinity of the supernova remnant Cassiopeia A. A light echo is created when a star explodes or erupts, flashing light into surrounding clumps of interstellar dust and causing them to shine in an ever-expanding pattern. Webb’s exquisite resolution not only shows incredible detail within these light echoes, but also shows their expansion over the course of just a few weeks – a remarkably short timescale considering that most cosmic targets remain unchanged over a human lifetime.
Credit: NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)

Taking a CT Scan

The images from Webb’s NIRCam (Near-Infrared Camera) highlight a phenomenon known as a light echo. A light echo is created when a star explodes or erupts, flashing light into surrounding clumps of dust and causing them to shine in an ever-expanding pattern. Light echoes at visible wavelengths (such as those seen around the star V838 Monocerotis) are due to light reflecting off of interstellar material. In contrast, light echoes at infrared wavelengths are caused when the dust is warmed by energetic radiation and then glows.

The researchers targeted a light echo that had previously been observed by NASA’s retired Spitzer Space Telescope. It is one of dozens of light echoes seen near the Cassiopeia A supernova remnant – the remains of the star that exploded. The light echo is coming from unrelated material that is behind Cassiopeia A, not material that was ejected when the star exploded.

The most obvious features in the Webb images are tightly packed sheets. These filaments show structures on remarkably small scales of about 400 astronomical units, or less than one-hundredth of a light-year. (An astronomical unit, or AU, is the average Earth-Sun distance. Neptune’s orbit is 60 AU in diameter.)

“We did not know that the interstellar medium had structures on that small of a scale, let alone that it was sheet-like,” said Peek.

These sheet-like structures may be influenced by interstellar magnetic fields. The images also show dense, tightly wound regions that resemble knots in wood grain. These may represent magnetic “islands” embedded within the more streamlined magnetic fields that suffuse the interstellar medium.

“This is the astronomical equivalent of a medical CT scan,” explained Armin Rest of the Space Telescope Science Institute, a member of the science team. “We have three slices taken at three different times, which will allow us to study the true 3D structure. It will completely change the way we study the interstellar medium.”

Image B: Cassiopeia A (Spitzer with Webb Insets)

A background image in a shade of orange shows cloud-like structures filling the field of view, along with a handful of stars. At the middle of the image is a bright circle with a white box around it. Lines extend from the box to the left, where an inset image shows a multicolored ring of gaseous filaments in shades of pink and purple. At lower right of the background image, two smaller regions have white boxes around them. Lines extend from those to boxes above with two insets. Each inset displays dozens of white stars on the black background of space. They also contain tightly packed, red filaments that resemble muscle fibers or wood grain.
This background image of the region around supernova remnant Cassiopeia A was released by NASA’s Spitzer Space Telescope in 2008. By taking multiple images of this region over three years with Spitzer, researchers were able to examine a number of light echoes. Now, NASA’s James Webb Space Telescope has imaged some of these light echoes in much greater detail. Insets at lower right show one epoch of Webb observations, while the inset at left shows a Webb image of the central supernova remnant released in 2023.
Spitzer Image: NASA/JPL-Caltech/Y. Kim (Univ. of Arizona/Univ. of Chicago). Cassiopeia A Inset: NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGent), Tea Temim (Princeton University). Light Echoes Inset: NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC).

Future Work

The team’s science program also includes spectroscopic observations using Webb’s MIRI (Mid-Infrared Instrument). They plan to target the light echo multiple times, weeks or months apart, to observe how it evolves as the light echo passes by.

“We can observe the same patch of dust before, during, and after it’s illuminated by the echo and try to look for any changes in the compositions or states of the molecules, including whether some molecules or even the smallest dust grains are destroyed,” said Jencson.

Infrared light echoes are also extremely rare, since they require a specific type of supernova explosion with a short pulse of energetic radiation. NASA’s upcoming Nancy Grace Roman Space Telescope will conduct a survey of the galactic plane that may find evidence of additional infrared light echoes for Webb to study in detail.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

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Media Contacts

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

Christine Pulliamcpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.

Science – Jacob Jencson (Caltech/IPAC)

Articles: Past Webb news releases on Cassiopeia A

Interactive: Explore light echoes in V838 Monocerotis

Videos: Learn more about supernovas.

More Webb News

More Webb Images

Webb Science Themes

Webb Mission Page

What is a supernova?

What is the Webb Telescope?

SpacePlace for Kids

En Español

Ciencia de la NASA

NASA en español 

Space Place para niños

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      Last Updated May 04, 2025 Editor Marty McCoy Contact Laura Betz laura.e.betz@nasa.gov Related Terms
      James Webb Space Telescope (JWST) Astrophysics Exoplanets Goddard Space Flight Center Science & Research The Universe View the full article
    • By NASA
      3 min read
      Help Classify Galaxies Seen by NASA’s James Webb Space Telescope!
      The Galaxy Zoo classification interface shows you an image from NASA’s Webb telescope and asks you questions about it. Image credit: Galaxy Zoo, Zooniverse. Inset galaxy: NASA/STScI/CEERS/TACC/S. Finkelstein/M. Bagley/Z. Levay/A. Pagan NASA needs your help identifying the shapes of thousands of galaxies in images taken by our James Webb Space Telescope with the Galaxy Zoo project. These classifications will help scientists answer questions about how the shapes of galaxies have changed over time, what caused these changes, and why. Thanks to the light collecting power of Webb, there are now over 500,000 images of galaxies on website of the Galaxy Zoo citizen science project—more images than scientists can classify by themselves. 
      “This is a great opportunity to see images from the newest space telescope,” said volunteer Christine Macmillan from Aberdeen, Scotland. “Galaxies at the edge of our universe are being seen for the first time, just as they are starting to form. Just sign up and answer simple questions about the shape of the galaxy that you are seeing. Anyone can do it, ages 10 and up!”  
      As we look at more distant objects in the universe, we see them as they were billions of years ago because light takes time to travel to us. With Webb, we can spot galaxies at greater distances than ever before. We’re seeing what some of the earliest galaxies ever detected look like, for the first time. The shapes of these galaxies tell us about how they were born, how and when they formed stars, and how they interacted with their neighbors. By looking at how more distant galaxies have different shapes than close galaxies, we can work out which processes were more common at different times in the universe’s history.   
      At Galaxy Zoo, you’ll first examine an image from the Webb telescope. Then you will be asked several questions, such as ‘Is the galaxy round?’, or ‘Are there signs of spiral arms?’. If you’re quick, you may even be the first person to see the galaxies you’re asked to classify.  
      “I’m amazed and honored to be one of the first people to actually see these images! What a privilege!” said volunteer Elisabeth Baeten from Leuven, Belgium.
      Galaxy Zoo is a citizen science project with a long history of scientific impact. Galaxy Zoo volunteers have been exploring deep space since July 2007, starting with a million galaxies from a telescope in New Mexico called the Sloan Digital Sky Survey and then, moving on to images from space telescopes like NASA’s Hubble Space Telescope and ESA (European Space Agency)’s Euclid telescope. The project has revealed spectacular mergers, taught us about how the black holes at the center of galaxies affect their hosts, and provided insight into how features like spiral arms form and grow.  
      Now, in addition to adding new data from Webb, the science team has incorporated an AI algorithm called ZooBot, which will sift through the images first and label the ‘easier ones’ where there are many examples that already exist in previous images from the Hubble Space Telescope. When ZooBot is not confident on the classification of a galaxy, perhaps due to complex or faint structures, it will show it to users on Galaxy Zoo to get their human classifications, which will then help ZooBot learn more. Working together, humans and AI can accurately classify limitless numbers of galaxies. The Galaxy Zoo science team acknowledges support from the International Space Sciences Institute (ISSI), who provided funding for the team to get together and work on Galaxy Zoo. Join the project now.  
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      Details
      Last Updated Apr 29, 2025 Related Terms
      Astrophysics Division Citizen Science Get Involved James Webb Space Telescope (JWST) Explore More
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    • By NASA
      NASA/Johns Hopkins APL/Princeton/Ed Whitman NASA’s IMAP (Interstellar Mapping and Acceleration Probe) is loaded into the X-ray and Cryogenic Facility (XRCF) thermal vacuum chamber at NASA’s Marshall Space Flight Center in Huntsville, Alabama, in this photo from March 20, 2025. There, the spacecraft will undergo testing such as dramatic temperature changes to simulate the harsh environment of space.
      The IMAP mission is a modern-day celestial cartographer that will map the solar system by studying the heliosphere, a giant bubble created by the Sun’s solar wind that surrounds our solar system and protects it from harmful interstellar radiation. The IMAP mission will launch on a SpaceX Falcon 9 rocket from NASA’s Kennedy Space Center in Florida, no earlier than September 2025.
      Image credit: NASA/Johns Hopkins APL/Princeton/Ed Whitman
      View the full article
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