Mysterious features hide in near infrared light
Like a shiny, round ornament ready to be placed in the perfect spot on the holiday tree, the remnant of the supernova Cassiopeia A (Cas A) shines in a new image from NASA’s James Webb Space Telescope. as part of Holidays 2023 at the White House, First Lady of the United States Dr. Jill Biden launched the first-ever White House Advent Calendar. To showcase the “magic, wonder, and joy” of the holiday season, Dr. Biden and NASA are celebrating with this new image from Webb.
While all is bright, this scene is not the proverbial silent night. Cas A’s Webb NIRCam (near infrared camera) displays this starburst at a resolution previously unattainable at these wavelengths. This high-resolution view reveals intricate details of the expanding shell of material colliding with gas released by the star before it exploded.
Cas A is one of the most well-studied supernova remnants in all of the universe. Over the years, ground-based and space-based observatories, including NASA Chandra X-ray Observatory, Hubble Space TelescopeAnd retired Spitzer Space Telescope They compiled a multi-wavelength image of the body’s remains.
However, astronomers have now entered a new era in the study of Cas A. In April 2023, Webb’s MIRI instrument (Mid-Infrared Instrument) was discovered. This chapter has begun, revealing new and unexpected features within the inner shell of the supernova remnant. Many of these features are not visible in the new NIRCam image, and astronomers are investigating why.
Image: Cassiopeia A (NIRCam)
“Like shards of glass”
Infrared light is invisible to our eyes, so image processors and scientists translate these wavelengths of light into visible colors. In this newer image of Cas A, the colors are assigned to different NIRCam filters, and each of these colors indicates a different activity occurring within the object.
At first glance, the NIRCam image may appear less colorful than the MIRI image. However, this is simply due to the wavelengths at which the material of the object emits its light.
The most visible colors in Webb’s new image are the bright orange and light pink clumps that make up the inner crust of the supernova remnant. Webb’s sharp vision can detect the smallest knots of gas, made up of sulfur, oxygen, argon and neon, from the star itself. In this gas is a mixture of dust and particles, which will eventually become components of new stars and planetary systems. Some of the debris filaments are so small that even Loeb can’t resolve them, meaning they are comparable to or less than 10 billion miles (about 100 astronomical units) across. By comparison, the entirety of Cas A spans 10 light-years, or 60 trillion miles.
“Thanks to the resolution of NIRCam, we can now see how the dying star completely shattered as it exploded, leaving behind filaments that resemble tiny glass shards,” said Dani Milisavljevic of Purdue University, who leads the research team. “It is truly incredible that after all these years of studying Cas A we can now resolve these details, which provide us with transformative insight into how this star exploded.”
Image: Cassiopeia A NIRCam/MIRI
The hidden green monster
When comparing Webb’s new near-infrared view of Cas A with the mid-infrared view, its inner cavity and outer shell are strangely colorless.
The edges of the main inner shell, which appeared in deep orange and red in the MIRI image, now look like smoke from a campfire. This refers to where the supernova’s explosion wave collides with the material surrounding the star. The dust in the material surrounding the star is too cold to be detected directly at near-infrared wavelengths, but it glows in the mid-infrared.
The researchers say the white color is light from synchrotron radiation, which is emitted across the electromagnetic spectrum, including near infrared. They are generated by charged particles traveling at extremely high speeds and wrapping around magnetic field lines. Synchrotron radiation is also visible in the bubble-like shells in the lower half of the inner cavity.
Also missing from the near-infrared image was the green light ring in Cas A’s central cavity that glowed in the mid-infrared, which the research team called the Green Monster. This feature was described as “difficult to understand” by researchers upon first looking at them.
While the green color of the green monster is not visible in NIRCam, what remains of near-infrared light in that region could provide insight into this mysterious feature. The circular holes visible in the MIRI image are faintly outlined by white and purple emission in the NIRCam image – this represents ionized gas. Researchers believe this is due to supernova debris rushing through the gas and forming the gas left behind by the star before it exploded.
Photo: Features of Chair A
Baby Cass A
The researchers were also amazed by a remarkable feature in the lower right corner of NIRCam’s field of view. They call that big, striped blob Baby Cas A, because it looks like the descendant of a major supernova.
This is a light echo, where the light from the star’s explosion arrived long ago, heating up the distant dust, which glows as it cools. The complexity of the dust pattern, and the apparent closeness of Baby Cas A to Cas A itself, particularly interests researchers. In fact, Baby Cas A is located about 170 light-years beyond the supernova remnant.
There are also many smaller light echoes scattered throughout the new Webb image.
The Cas A supernova remnant is located 11,000 light-years away in the constellation Cassiopeia. It is estimated to have exploded about 340 years ago from our perspective.
The James Webb Space Telescope is the world’s leading space science observatory. Webb solves the mysteries of our solar system, looks beyond the distant worlds around other stars, and explores the mysterious structures and origins of our universe and our place in it. WEB is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Download full resolution images for this article From the Space Telescope Science Institute.
View/download a video tour of Cassiopeia A From the Space Telescope Science Institute.
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