NASA’s Webb Unveils the Hidden Beauty of Cosmic Dust and Gas Layers

Once upon a time, the core of an enormous star imploded, generating a shockwave that surged outward, tearing the star apart as it progressed. When that shockwave hit the star’s surface, it punctured through, causing a fleeting, intense burst of X-rays and ultraviolet light that spread outward into the surrounding void. Roughly 350 years later, this burst of light reached interstellar matter, illuminating it, warming it, and prompting it to radiate in infrared light. 

Nasa’s James Webb Space Telescope has captured that infrared radiance, unveiling intricate details akin to the knots and spirals in wood grain. These discoveries are enabling astronomers to chart the genuine 3D architecture of this interstellar dust and gas (referred to as the interstellar medium) for the very first time.

“We were quite amazed to observe this degree of intricacy,” remarked Jacob Jencson from Caltech/IPAC in Pasadena, principal investigator of the research program.

“We can see layers similar to an onion,” added Josh Peek of the Space Telescope Science Institute in Baltimore, a member of the scientific team. “We believe that every dense, dusty area we observe—and most of the ones we cannot see—appear like this internally. We simply have never had the opportunity to inspect their interiors previously.”

The group is showcasing their findings during a press briefing at the 245th assembly of the American Astronomical Society in National Harbor, Maryland.

“Even as a star comes to its end, its light persists—resonating throughout the cosmos. The past three years since the launch of NASA’s James Webb Space Telescope have been remarkable. Each image, each discovery, portrays not only the grandeur of the universe but also the strength of the NASA crew and the potential of international collaborations. This pioneering mission, NASA’s most significant international space science partnership, is a genuine testament to NASA’s ingenuity, teamwork, and quest for excellence,” stated NASA Administrator Bill Nelson. “What an honor it has been to oversee this monumental initiative, shaped by the unwavering commitment of thousands of scientists and engineers globally. This most recent image precisely encapsulates Webb’s enduring legacy—a glimpse into the past and a mission that will inspire future generations.”

Conducting a CT Scan

The visuals from Webb’s NIRCam (Near-Infrared Camera) highlight a phenomenon referred to as a light echo. A light echo occurs when a star detonates or bursts, transmitting light into adjoining clusters of dust and making them shimmer in a continually expanding pattern. Light echoes at visible wavelengths (such as those observed around the star V838 Monocerotis) result from light reflecting off interstellar matter. However, light echoes at infrared wavelengths arise when dust is heated by energetic radiation and subsequently glows.

The researchers focused on a light echo that had previously been observed by NASA’s retired Spitzer Space Telescope. It is one of many light echoes identified near the Cassiopeia A supernova remnant – the remnants of the star that exploded. The light echo is emanating from unrelated material located behind Cassiopeia A, not from material that was expelled during the star’s explosion.

The most discernible features in the Webb images are densely packed sheets. These filaments demonstrate structures on astonishingly small scales of around 400 astronomical units, or less than one-hundredth of a light-year. (An astronomical unit, or AU, denotes the mean distance between the Earth and the Sun; Neptune’s orbit spans 60 AU in diameter.)

“We were unaware that the interstellar medium exhibited structures on such small scales, let alone that they were sheet-like,” explained Peek.

These sheet-like formations may be influenced by interstellar magnetic fields. The images further reveal dense, tightly coiled areas that resemble knots in wood grain. These may signify magnetic “islands” nestled within the more streamlined magnetic fields permeating the interstellar medium.

“This is the astronomical equivalent of a medical CT scan,” described Armin Rest from the Space Telescope Science Institute, a member of the research team. “We have three cross-sections taken at three distinct times, which will enable us to examine the actual 3D structure. It will fundamentally alter how we study the interstellar medium.”

Future Endeavors

The team’s research agenda also encompasses spectroscopic observations utilizing Webb’s MIRI (Mid-Infrared Instrument). They intend to target the light echo multiple times, weeks or months apart, to monitor how it transforms as the light echo moves past. 

“We can scrutinize the same area of dust before, during, and after it is illuminated by the echo, searching for any alterations in the compositions or states of the molecules, including whether some molecules or even the tiniest dust grains are obliterated,” Jencson noted.

Infrared light echoes are also notably scarce, requiring a specific kind of supernova explosion with a brief burst of energetic radiation. NASA’s forthcoming Nancy Grace Roman Space Telescope will conduct a survey of the galactic plane that may uncover indications of additional infrared light echoes for Webb to analyze in depth.

The James Webb Space Telescope is the globe’s foremost space science observatory. Webb is unraveling enigmas within our solar system, peering beyond to distant realms around other stars, and exploring the enigmatic structures and origins of our universe and our place within it. Webb is an international initiative led by NASA alongside its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).