While the human eye is an amazing evolutionary creation, it simply can’t witness the full grandeur of the universe. Glimpsing the same celestial object in the visual spectrum can look dramatically different compared to other, “invisible” wavelengths, and the latest photo from NASA’s James Webb Space Telescope (JWST) only highlights our biological limitations with stunning clarity.
JWST’s Near Infrared Camera (NIRCam) recently captured this image of the Cassiopeia A supernova remnant: the aftermath of a giant star’s explosive death 11,000 light years away and 340 years ago (from our perspective). If you saw JWST’s mid-infrared image of Cassiopeia A earlier this year, the roiling, rapidly expanding cloud of hot gas and dust looks almost unrecognizable in the new image.
Mid-Infrared Instrument (MIRI) and NIRcam see the universe in slightly different wavelengths of light, so they show us very different aspects of the same object, which include varying chemical compounds and physical processes. Those unique perspectives may shed some new light on how massive stars die, evolve, and eventually seed the universe with the ingredients for new star systems.
The Aftermath of Cosmic Violence
All the twisted filaments of fiery orange and magenta in this image are roiling clouds of gas, which span 60 trillion miles (about 10 light-years) of space. All that material used to be packed into the interior of a giant star that was a mix of sulfur, oxygen, argon, and neon — all forged in the fires of thermonuclear fusion. Now, these elements are a rapidly spreading cloud of gas/dust debris that glows in a shorter wavelength than our eyes can see. To make JWST’s “invisible” data visible to our eyes, a team of image processors and astronomers choose visible colors to represent each wavelength of otherwise invisible infrared light.
The turbulence of those filaments and knots is thanks in part to the violence of the explosion that ripped the star apart and blasted its innards into space. However, the other part of this stellar equation also involves an onrushing debris cloud colliding with a slower-moving wave of stellar debris.
As a massive star is preparing to die, it shrugs off its outer layers, which drift slowly outward into space. Sometime later, when the explosive end finally comes, the blast wave rushes outward and rapidly catches up with what’s left of the star’s outer layers. The result is a messy, violent collision between two walls of gas and dust, which rips and twists the debris cloud into tattered filaments and clumps.
Seeing Things in a Different Light
Despite all that drama, this image looks sparse compared to an earlier glimpse of the same roiling debris cloud, captured earlier this year with MIRI. This JWST instrument sees the universe in slightly longer wavelengths of infrared light, and it’s hard to tell you’re even looking at the same object. While this isn’t the first time we’ve seen this kind of comparison, it continues to be extremely awe-inspiring. *You can compare the two by sliding a filter back and forth here.)
In the MIRI image, you can see the billows of deep orange and red gas around the expanding debris cloud, which is the slower-moving cloud that used to be the star’s outermost layers. But in this latest NIRCam image, those outer layers are faint, barely-visible wisps of pale gray. That’s because the star’s shrugged-off outer layers are laden with dust, which is cooler than the hot gas of the supernova debris cloud. Hotter objects tend to glow in shorter wavelengths, like near-infrared, and the cooler dust shows up only in longer, cooler mid-infrared.
One of the Cassiopeia A supernova remnant’s biggest mysteries is almost completely invisible in the new NIRCam image, but even its absence may give astronomers some clues. In April’s MIRI image, you can see a huge whorl of glowing green in the center of the image, arcing across an area of space that the debris cloud has already traversed. Astronomers dubbed this arc of green light the “Green Monster” and describe it as “challenging to understand.” But in the NIRCam image, the Green Monster is invisible, which means whatever it is, it’s glowing in mid-infrared but not in near-infrared. Comparing the two images – as well as the valuable data they represent – may help astronomers understand the physics behind the monstrous yet gorgeous phenomenon.
But that isn’t the end of Cassiopeia’s A growingly list of cosmic questions as something entirely new showed up in this new NIRCam image: a glowing blob in the lower right corner of the image, which looks like a baby version of the supernova remnant. This cloud of dust is actually 170 light-years “behind” the supernova (from our vantage point), which has been heated by the star’s explosion. As that supernova-scorched dust slowly cools, it glows in near-infrared, creating what astronomers call a “light echo.”
As these new images more than show, when exploring the complicated science of the known universe, it definitely helps to have a few robotic eyes in orbit capable of glimpsing the invisible.
