by The intricate whorls and streaks of dust floating among the stars have just been revealed in astonishing detail.
In new images from JWST, we finally see beautiful details of the flow and turbulence of the interstellar medium near a star we saw explode just a few hundred years ago.
As light from the explosion, which we now call Cassiopeia A, extended outward, it reflected and heated the thin dust it passed through, generating a faint, red lambence.
So faint is the material, and so faint the glow, that its true complexity has largely escaped us. Now, thanks to JWST’s power to see dim, red light, we’re finally getting a better understanding of the structure of the interstellar medium.
What’s even more incredible is that we can see changes in the structure at the scale of to dawn. JWST took multiple images of a dome in the dust cloud near Cassiopeia A in August and September 2024, and saw significant changes as light moved through the wood-grained streaks, producing a phenomenon known as a light echo.
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“We see layers like an onion,” says astronomer Josh Peek of the Space Telescope Science Institute in the US. “We think every dense, dusty region we see, and most of the ones we don’t see, looks like this inside. We’ve never been able to look inside it before.”
Light echoes can produce some of the most beautiful sights in the galaxy. They occur when something produces a flash of light that radiates into space.
If that light encounters a physical barrier, such as clouds of cosmic dust, it will reflect, arriving at a different time than the initial burst; Just like a sound echo, but with light. We can use these light echoes to map and understand space, and the objects in it.
To date, most of the bright echoes we have detected tend to be from very bright events or very thick dust close to the light source, as we see in the star V838 monocerotis. Thinner dust, further from the source, is a lot harder to see.
But hey, seeing things we couldn’t see before is what JWST does. The infrared telescope is optimized to see the faint red light that other instruments cannot pick up; So astronomers turned it into a mess of dust near and behind, but not related to, Cassiopeia A, a star that humanity saw explode from 11,000 light-years away in the 1670s.
This Wisp was identified as a light echo by NASA’s now retired Spitzer Space Telescope. But Spitzer didn’t have JWST’s resolution.
Still, “we were quite shocked to see this level of detail,” says astronomer Jacob Jencson of the California Institute of Technology.
Perhaps most surprising was the discovery that the medium is arranged in tightly packed sheets of material, with knots and whorls, somewhat like the knots you might see in the grain of a tree. The researchers were able to see details in these sheets down to scales of about 400 astronomical units, or 400 times the distance between Earth and the Sun.
These structures, the researchers believe, may be related to magnetic field lines running through space. If this is the case, studying the evolution of light echoes opens a new window in the study of magnetized turbulence.
“This is the astronomical equivalent of a medical CT scan,” says astronomer Armin Rest of the Space Telescope Science Institute. “We took three slices 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.”
Furthermore, in-depth analyzes of the observations are undoubtedly forthcoming.
Meanwhile, two presentations, one led by Jencson, the other by Peek, took place at the 245th meeting of the American Astronomical Society. You can find the summaries here and here.
