NASA’s James Webb Space Telescope studied the infrared glow, which revealed minute details similar to the knots and whorls of wood grain. These findings enable astronomers to study the full 3D structure of interstellar dust and gas (known as the interstellar medium) for the first time.
This shimmering cosmic curtain shows interstellar gas and dust 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. Image Credit: NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)
In history, a gigantic star's core collapsed, sending a shockwave outward that tore the star apart. When the shockwave struck the star's surface and spread out into the surrounding cosmos, a brief, powerful pulse of X-rays and ultraviolet light was produced. That light pulse reached interstellar material some 350 years later, warming it, illuminating it, and making it glow in infrared light.
We were pretty shocked to see this level of detail.
Jacob Jencson, National Science Foundation Graduate Research Fellow, Department of Astronomy, California Institute of Technology
“We see layers like an onion,” added Josh Peek of the Space Telescope Science Institute in Baltimore, a science team member. “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 holding a press conference to present their findings 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.
Bill Nelson, Administrator, NASA
Nelson added, “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.”
Taking a CT Scan
The images taken by Webb's NIRCam (Near-Infrared Camera) highlight a phenomenon called a light echo. When a star erupts or explodes, light is flashed into nearby dust clumps, forcing them to shine in an ever-expanding pattern, creating a light echo.
Light bouncing off of interstellar material is the cause of light echoes at visible wavelengths, like those observed orbiting the star V838 Monocerotis. On the other hand, when the dust is warmed by intense radiation and then glows, light echoes at infrared wavelengths are produced.
The researchers focused on a light echo that NASA's retired Spitzer Space Telescope had previously seen. It is one of the dozens of light echoes observed near the Cassiopeia A supernova remnant, a relic of the exploding star. The source of the light echo is not material ejected when the star exploded but unrelated material behind Cassiopeia A.
Tightly packed sheets are the Webb images' most noticeable characteristics. Approximately 400 astronomical units, or less than one-hundredth of a light-year, are the extraordinarily small scales at which these filaments display features. The average distance between Earth and the Sun is known as an astronomical unit or AU. The diameter of Neptune’s orbit is 60 AU.)
Peek added, “We did not know that the interstellar medium had structures on that small of a scale, let alone that it was sheet-like.”
Interstellar magnetic fields could alter these sheet-like formations. The images also depict dense, tightly wrapped regions resembling wood grain knots. These may be magnetic “islands” among the more streamlined magnetic fields that pervade the interstellar medium.
This is the astronomical equivalent of a medical CT scan. 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.
Armin Rest, Member, Science Team, Space Telescope Science Institute
Future Work
The team’s science program includes spectroscopic investigations with Webb’s MIRI (Mid Infrared Instrument). They intend to target the light echo several times, weeks or months apart, to see how it changes as it passes by.
“We can observe the same patch of dust before, during, and after it is 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,” further added Jencson.
Infrared light echoes are likewise extremely rare, necessitating a certain form of supernova explosion with a brief burst of energetic radiation. NASA’s scheduled Nancy Grace Roman Space Telescope will explore the galactic plane, potentially revealing more infrared light echoes for Webb to investigate further.
Cassiopeia A Light Echoes Time-lapse
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.Video Credit: NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)