Mapping the Cosmos: Unraveling the Mysteries of Supernova Cassiopeia A

Long ago, the core of a giant star collapsed, producing a shockwave that surged outward, tearing the star apart in its path. When the shockwave touched the star’s exterior, it broke through, creating a fleeting, powerful surge of X-rays and ultraviolet light that propagated outward into the surrounding void. Approximately 350 years later, that flash of light has reached interstellar matter, illuminating, heating, and causing it to emit infrared light.

NASA’s James Webb Space Telescope has captured that infrared glow, uncovering intricate details similar to the knots and swirls of wood grain. These insights are enabling astronomers to delineate the actual 3D configuration of this interstellar dust and gas (termed the interstellar medium) for the very first time.

“We were quite astonished to observe this degree of detail,” remarked Jacob Jencson of Caltech/IPAC in Pasadena, the main investigator of the research initiative.

“We observe layers akin to those of an onion,” added Josh Peek from the Space Telescope Science Institute in Baltimore, a member of the scientific team. “We believe that every dense, dusty area that we detect, as well as most that we do not detect, presents this internal structure. We just have never had the opportunity to examine them from within before.

The team is sharing their discoveries at a press event during the 245th assembly of the American Astronomical Society in Washington.

“As a star perishes, its light persists—resonating throughout the universe. It has been an incredible three years since the launch of NASA’s James Webb Space Telescope. Each image, every revelation, illustrates not only the grandeur of the cosmos but also the capability of the NASA team and the potential of global collaborations. This pioneering mission, NASA’s most significant international space science partnership, is a remarkable testament to NASA’s creativity, collaboration, and commitment to excellence,” expressed NASA Administrator Bill Nelson. “What a privilege it has been to supervise this significant project, shaped by the relentless efforts of thousands of scientists and engineers worldwide. This latest image beautifully epitomizes the enduring legacy of Webb—a glimpse into history and a mission that will motivate future generations.”

These shining cosmic veils present interstellar gas and dust that has been elevated in temperature due to the blinding explosion of a long-ago supernova. The gas subsequently radiates infrared light in a phenomenon known as a thermal light echo. As the illumination from the supernova traverses through the cosmos at the speed of light, the echo appears to unfold. NASA’s James Webb Space Telescope investigated this light echo around the supernova remnant Cassiopeia A three distinct times, effectively creating a 3D map of the interstellar material. Be aware that the field of view in the top row is rotated slightly clockwise compared to the middle and bottom rows due to the observational angle of the Webb telescope at the time the data was gathered. NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC) Larger image

This time-lapse visualization utilizing data from NASA’s James Webb Space Telescope underscores the progression of one light echo near the supernova remnant Cassiopeia A. A light echo forms when a star detonates or erupts, projecting light into surrounding accumulations of interstellar dust and prompting them to illuminate in a continually expanding fashion. Webb’s remarkable resolution not only reveals astounding detail within these light echoes but also captures their expansion over the span of just a few weeks—a remarkably brief duration considering that most cosmic subjects remain unchanged throughout a human lifetime. Credit: NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)

Conducting a CT Scan

The images provided by Webb’s NIRCam (Near-Infrared Camera) spotlight a phenomenon termed a light echo. A light echo takes shape when a star detonates or erupts, sending light into surrounding clusters of dust, causing them to shine in a perpetually expanding layout. Light echoes within visible wavelengths (as evidenced around the star V838 Monocerotis) stem from light reflecting off interstellar material. Conversely, light echoes at infrared wavelengths occur when the dust is heated by intense radiation and then emits light.

The researchers focused on a light echo that had been previously documented by NASA’s retired Spitzer Space Telescope. It is one amongst numerous light echoes discovered close to the Cassiopeia A supernova remnant – the remains of the star that exploded. The light echo is emerging…from irrelevant material situated behind Cassiopeia A, rather than material expelled during the star’s explosion.

The most evident characteristics in the Webb images are closely arranged sheets. These filaments exhibit formations on astonishingly small scales of approximately 400 astronomical units, or less than one-hundredth of a light-year. (An astronomical unit, or AU, is the average distance between Earth and the Sun. Neptune’s orbit measures 60 AU across.)

“We were unaware that the interstellar medium contained structures on such a diminutive scale, much less that they were sheet-like,” commented Peek.

These sheet-like formations might be affected by interstellar magnetic fields. The images also display dense, tightly coiled areas that resemble knots within wood grain. These may signify magnetic “islands” embedded within the more streamlined magnetic fields that permeate the interstellar medium.

“This is the astronomical equivalent of a medical CT scan,” described Armin Rest of the Space Telescope Science Institute, a member of the scientific team. “We have three slices taken at three different intervals, which will enable us to investigate the genuine 3D structure. It will completely transform the way we examine the interstellar medium.”

This background image depicting the area surrounding supernova remnant Cassiopeia A was released by NASA’s Spitzer Space Telescope in 2008. By capturing multiple images of this region over three years with Spitzer, researchers could observe several light echoes. Now, NASA’s James Webb Space Telescope has captured some of these light echoes in significantly greater detail. Insets at the lower right show one time frame of Webb observations, while the inset on the left represents 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). Larger image

Future Research

The team’s scientific initiative also encompasses spectroscopic observations using Webb’s MIRI (Mid-Infrared Instrument). They intend to focus on the light echo multiple times, weeks or months apart, to monitor its evolution as it progresses.

“We can observe the same section of dust before, during, and after it is illuminated by the echo and attempt to look for any alterations in the compositions or states of the molecules, including whether certain molecules or even the tiniest dust particles are obliterated,” stated Jencson.

Infrared light echoes are also exceedingly uncommon, as they necessitate a specific type of supernova explosion exhibiting a brief pulse of high-energy radiation. NASA’s forthcoming Nancy Grace Roman Space Telescope will conduct a survey of the galactic plane that may uncover instances of additional infrared light echoes for Webb to investigate in detail.

The James Webb Space Telescope is the world’s leading space science observatory. Webb is unraveling mysteries within our solar system, exploring far-off worlds orbiting other stars, and probing the enigmatic structures and origins of our universe and our position within it. Webb is an international endeavor spearheaded by NASA alongside its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

Astrobiology, Astrochemistry, Astronomy,