Webb Unveils the Hidden Tapestry of Interstellar Dust and Gas

Once long ago, the core of an immense star underwent collapse, generating a shockwave that forcefully projected outward, tearing the star apart. Upon reaching the surface, this shockwave broke through, resulting in a short, intense burst of X-rays and ultraviolet light that spread outward into the surrounding cosmos. Approximately 350 years later, that burst has illuminated interstellar material, warming it and inducing an infrared glow.

NASA’s James Webb Space Telescope has detected this infrared luminescence, revealing intricate configurations akin to the knots and whorls found in wood grain. These findings empower astronomers to accurately chart the genuine 3D composition of this interstellar dust and gas (commonly referred to as the interstellar medium) for the very first time.

“We were quite astonished to observe such a level of detail,” remarked Jacob Jencson from Caltech/IPAC in Pasadena, the principal investigator of the scientific initiative.

“We observe layers reminiscent of an onion,” added Josh Peek from the Space Telescope Science Institute in Baltimore, a member of the scientific team. “We suspect that every dense, dusty segment we perceive, and many that we are unaware of, resemble this on the interior. We simply have never had the opportunity to explore inside them before.”

The team is disclosing their results during a press briefing at the 245th conference of the American Astronomical Society in Washington.

“Even as a star meets its end, its luminosity persists—resonating throughout the universe. It has been an incredible three years since the launch of NASA’s James Webb Space Telescope. Every image, every discovery portrays a depiction not only of the grandeur of the cosmos but also the strength of the NASA team and the potential of global collaborations. This pioneering mission, NASA’s most extensive international space science partnership, stands as a testament to NASA’s creativity, collaboration, and quest for excellence,” stated NASA Administrator Bill Nelson.

“It has been a privilege to supervise this remarkable undertaking, shaped by the relentless commitment of countless scientists and engineers worldwide. This latest image strikingly embodies 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) emphasize a phenomenon referred to as a light echo. A light echo is produced when a star detonates or erupts, emitting light into surrounding dust clumps and making them shine in a continuously widening design. Light echoes at visible wavelengths (like those witnessed near the star V838 Monocerotis) occur due to light reflecting off interstellar material. Conversely, light echoes observed at infrared wavelengths happen when dust is heated by intense radiation and then glows.

The scientists focused on a light echo previously recorded by NASA’s retired Spitzer Space Telescope. It represents one of many light echoes detected near the Cassiopeia A supernova remnant—the remnants of the star that detonated. The light echo originates from unrelated matter 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 reveal structures on remarkably minute scales of roughly 400 astronomical units, or less than one-hundredth of a light-year. (An astronomical unit, or AU, is the mean distance between the Earth and the Sun. Neptune’s orbit spans 60 AU in diameter.)

“We were unaware that the interstellar medium possessed structures on such a small scale, especially that they were sheet-like,” stated Peek.

These sheet-like formations may be affected by interstellar magnetic fields. The imagery also displays dense, tightly grouped regions that resemble knots in wood grain. These could signify magnetic “islands” embedded within the more streamlined magnetic fields that permeate the interstellar medium.

“This represents the astronomical equivalent of a medical CT scan,” clarified Armin Rest of the Space Telescope Science Institute, a member of the science team. “We have three slices obtained at three different times, which will enable us to explore the genuine 3D structure. It will completely transform the approach we take in studying the interstellar medium.”

Upcoming efforts

The team’s scientific program further encompasses spectroscopic observations utilizing Webb’s MIRI (Mid-Infrared Instrument). They intend to focus on the light echo multiple times, weeks or months apart, to monitor how it transforms as the light echo passes through.

“We can observe the same area of dust before, during, and after it’s illuminated by the echo and attempt to identify any alterations in the compositions or states of the molecules, including whether certain molecules or even the smallest dust particles are obliterated,” mentioned Jencson.

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