NASA has published a stunning new image from the James Webb Space Telescope that shows the remnants of a star that exploded 343 years ago.
The new image of supernova remnant Cassiopeia A is the highest resolution so far. Cas A, which has been studied for hundreds of years, is 11,000 light-years distant in the famous W-shaped northern constellation of Cassiopeia. Cas A is 10 light-years across.
Expanding Shell
The colorful image shows an expanding shell of material hitting the gas shed by the star before it exploded. It was taken using Webb’s Near-Infrared Camera, which sees light as heat, enabling data to be collected at new wavelengths. Colors are assigned to different filters from NIRCam, which allows us to see an image.
Previous attempts at imaging it have come from ground-based and space-based observatories, including NASA’s Chandra X-Ray Observatory, the Hubble Space Telescope and the Spitzer Space Telescope.
Side By Side
An image of Cas A was previously taken using Webb’s Mid-Infrared Instrument, a near-infrared imager. Compare the two and Webb’s new NIRCam version appears less colourful. That’s because heat signatures light up in different wavelengths. MIRI shows the outskirts of the main inner shell—where the supernova blast wave is striking a bubble of gas previously emitted by the star as it inched towards going supernova—as deep orange and red. NIRCam gives it a far less distinct smokey look.
The white light is synchrotron radiation, something emitted across the electromagnetic spectrum.
Supernova Echo
Look at the bottom right corner of the NIRCam image, and you’ll see a blob. It’s about 170 light-years behind the supernova remnant. Researchers believe it to be a light echo from the star’s explosion, which is warming dust that’s glowing as it cools down. It’s been nicknamed “Baby Cas A,” but it is the largest of several other, smaller light echoes in the NIRCam image.
Guest Star
In 1181 when astronomers in China and Japan recorded a so-called “guest star” appearing in Cassiopeia for 185 days, after which it disappeared.
It would have been easily noticeable because Cassiopeia is a prominent contsellation. Look to the north from the northern hemisphere this month and you’ll see its famous W-shape. Once you’ve seen its five bright stars in a familiar shape, you’ll never be able to un-see it, not only because it’s so recognizable, but because it’s a circumpolar constellation—it revolves around the north star—so it’s almost always in the northern hemisphere’s night sky.
Wishing you clear skies and wide eyes.
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