Objects in space offer diverse insights into their composition and behaviors when observed across various wavelengths of light. Among the extensively studied entities within the Milky Way is the supernova remnant Cassiopeia A (Cas A).
Cassiopeia A. NIRCam Image. Image Credit: Space Telescope Science Institute.
Despite intensive scrutiny across the wavelength spectrum, this celestial body retains undisclosed mysteries within its fragmented remnants.
The unveiling of these enigmas is currently underway, facilitated by NASA's James Webb Space Telescope, one of the latest additions to researchers' toolkits. Webb's recent examination of the near-infrared spectrum has astounded researchers with its revelations, shedding new light on Cas A's intricate characteristics.
In a stunning image released by NASA’s James Webb Space Telescope, supernova remnant Cassiopeia A (Cas A) gleams like a brilliant, round ornament waiting to be placed in the ideal location on a holiday tree.
First Lady of the United States, Dr. Jill Biden, unveiled the first-ever White House Advent Calendar during the 2023 Holidays at the White House. Dr. Biden and NASA are commemorating the holiday season with this new Webb image, which aims to highlight the “Magic, Wonder, and Joy.”
Amidst the dazzling display, this celestial scene is anything but a metaphorical silent night. The James Webb Space Telescope's NIRCam (Near-Infrared Camera) captures Cassiopeia A in a level of detail previously unattainable at near-infrared wavelengths. This heightened resolution reveals the intricate dynamics of the expanding shell of matter colliding with the stellar remnants, showcasing the impact of the star's ejected gas before its cataclysmic explosion.
Among all the supernova leftovers in the universe, Cas A has undergone the most research. A multiwavelength image of the object’s remnant has been pieced together over time by ground- and space-based telescopes such as NASA’s Chandra X-Ray Observatory, Hubble Space Telescope, and retired Spitzer Space Telescope.
But the study of Cas A has now moved into a new phase for astronomers. This chapter was initiated in April 2023 by Webb’s MIRI (Mid-Infrared Instrument), which unveiled novel and surprising characteristics in the supernova remnant's inner shell. Astronomers are examining why several of those features are not visible in the newly acquired NIRCam image.
“Like Shards of Glass”
Image processors and scientists translate the wavelengths of infrared light to visible colors as it is invisible to human eyes. In this latest image of Cas A, distinct colors were allocated to various NIRCam filters, each indicating different activities ongoing within the object.
At first glance, the NIRCam image may seem less colorful than the MIRI image. But all this boils down to is the wavelengths at which the object’s substance is producing light.
The vivid orange and light pink clusters that comprise the supernova remnant's inner shell are the most prominent colors in Webb's most recent photograph. The smallest knots of gas, which are made up of argon, neon, sulfur, and oxygen, can be seen in Webb's incredibly fine image of the star.
A mixture of molecules and dust are embedded in this gas and will eventually form new stars and planetary systems. Some debris filaments are equivalent to or less than 10 billion miles across (about 100 astronomical units), making them too small for even Webb to discern. By contrast, the whole Cas A is 60 trillion miles, or 10 light-years, across.
With NIRCam’s resolution, we can now see how the dying star absolutely shattered when it exploded, leaving filaments akin to tiny shards of glass behind. It’s really unbelievable after all these years studying Cas A to now resolve those details, which are providing us with transformational insight into how this star exploded.
Danny Milisavljevic, Lead Researcher, Purdue University
Hidden Green Monster
In contrast to the mid-infrared view, Webb’s new near-infrared image of Cas A shows that its outermost shell and inner chamber are oddly colorless.
The primary inner shell’s periphery, which in the MIRI image showed up as a deep orange and red color, now resembles campfire smoke. This is the point where the surrounding circumstellar material is being struck by the supernova blast wave. Although it glows in the mid-infrared, the dust in the circumstellar material is too chilly to be directly observed at near-infrared wavelengths.
Synchrotron radiation, which emits light across the electromagnetic spectrum, including the near-infrared, is responsible for the white color, according to researchers. It is produced by charged particles whirling around magnetic field lines at incredibly high speeds. Additionally, visible is synchrotron radiation in the lower half of the inner cavity's bubble-like shells.
The mid-infrared glow of a green light loop in Cas A’s central cavity, which the study team dubbed the Green Monster, is also invisible in the near-infrared view. Researchers characterized this trait as “challenging to understand” when they initially looked at it.
Even though NIRCam cannot capture the Green Monster’s “green,” the remaining near-infrared data in that area can shed light on the enigmatic feature. The NIRCam image shows a slight contour of white and purple emission around the circular holes shown in the MIRI image; this emission is indicative of ionized gas. Scientists conclude that this is caused by supernova debris piercing through and molding gas that the star had left behind before its explosion.
Baby Cas A
Another amazing discovery that completely astounded the researchers was located in the lower right corner of NIRCam’s field of vision. Because it resembles a progeny of the main supernova, scientists have named that big, striated blob Baby Cas A.
This is a light echo - distant dust is glowing as it cools down - that light from the star’s long-ago outburst has reached. Researchers find the intricate dust pattern and Baby Cas A’s apparent closeness to Cas A itself to be particularly fascinating. Actually, Baby Cas A is situated roughly 170 light-years behind the remnant of the supernova.
Webb’s new portrait also has a few additional, tiny light echoes strewn around it.
The Cas A in the Cassiopeia constellation, 11,000 light-years away, is a supernova remnant. It is thought to have exploded approximately 340 years ago.