New images from the James Webb Space Telescope (JWST) reveal stunning details of dust floating between the stars. These images show intricate patterns of flow and turbulence in the interstellar medium around a supernova known as Cassiopeia A, which exploded about 350 years ago.
As the light from this explosion spread through space, it warmed the surrounding dust, creating a faint red glow. This glow is so subtle that we haven’t been able to appreciate its complexity until now. JWST’s ability to capture dim, red light allows us to see these details like never before.
What’s fascinating is that JWST can detect changes in this dusty region over just a few days. In August and September 2024, the telescope captured multiple images of a specific dust wisp near Cassiopeia A. These images showed apparent changes as the light from the explosion passed through the dust, creating what scientists call a “light echo.” This process is similar to how sound echoes off walls.
“We see layers like an onion,” says astronomer Josh Peek. He explains that many dusty areas in space have similar structures that we’ve never examined closely before.
Light echoes can produce awe-inspiring visuals in the universe. When a flash of light encounters cosmic dust, it reflects back, arriving later than the original burst. This delay allows astronomers to map and understand the surrounding space better. Most of the echoes detected so far have come from bright events or dense dust clouds close to their light source, like the star V838 Monocerotis. However, thinner dust further away is much harder to spot.
JWST excels at revealing what was previously invisible. It targeted a wispy dust region connected to Cassiopeia A, a supernova observed from Earth in the 1670s, about 11,000 light-years away. NASA’s earlier Spitzer space telescope had noted the presence of this wisp but couldn’t capture the same level of detail.
Jacob Jencson, an astronomer at Caltech, was surprised by the level of detail captured by JWST. The images show that the dust is organized in tightly packed sheets with knots and whorled patterns, similar to tree grain. Researchers can now see these structures down to about 400 astronomical units, which is 400 times the distance from Earth to the Sun.
These findings could also relate to how magnetic fields flow through space. Studying how light echoes evolve may give us new insights into magnetized turbulence in the universe.
As Armin Rest, another astronomer, puts it, “This is like a medical CT scan for astronomy.” The three sets of images taken at different times allow researchers to study the genuine 3D structure of the interstellar medium in a whole new way.
More detailed analyses of these observations are on the way. Recently, presentations were made at the 245th Meeting of the American Astronomical Society, highlighting these exciting discoveries.
