Webb unveils stunning ejecta and CO structures in Cassiopeia A’s young supernova

The SETI Institute has announced the latest findings from the James Webb Space Telescope (JWST) investigation of the supernova remnant Cassiopeia A (Cas A). These observations of the youngest known core-collapse supernova in the Milky Way galaxy provide insight into the conditions that lead to the formation and destruction of molecules and dust within the supernova ejecta.

The findings of this study change our understanding. Dust The galaxy detected by JWST 300 million years after the Big Bang sheds light on its formation in the early universe. Researchers believe that supernovae like the one that formed Cassiopeia A are an important source of the dust seen in distant, high-redshift galaxies. These new findings call into question the conventional wisdom that dust originated primarily from intermediate-mass stars in the asymptotic giant branch (AGB) of present-day galaxies.

“The brightness of the carbon monoxide emission detected by JWST’s NIR imaging and spectroscopy is astonishing, showing a sinusoidal pattern of dozens of fundamental rotational vibrational lines of CO,” said Dr. Jeogie Lo, research scientist at the SETI Institute who led the study. “The pattern appears to be artificially generated.”

Key findings include:

1. Molecular CO formation: The data shows that there is more CO gas than argon gas in the outer layers, meaning that CO molecules are reforming after the backshock wave. This data is important for understanding how cooling and dust formation occurs after a supernova explosion. The images show that CO molecules reformed behind the shock wave, which may have protected the dust in the ejecta.
2. Detailed Spectroscopy: NIRSpec-IFU spectra of two key regions of CasA show differences in how elements are formed. Both regions have a strong CO gas signal, along with a variety of ionized elements such as argon, silicon, calcium, and magnesium. The fundamental CO line is a sinusoidal pattern of dozens of CO fundamental rotational vibration lines that form a continuum beneath it, due to the high speed of the CO molecule.
3. Temperature considerations: Based on the CO outgassing, the study indicates a temperature of approximately 1080 K. This is helpful for understanding how dust, molecules, and highly ionized gas interact in a supernova. However, the authors also found vibrational lines in the high rotation (J=90) lines, which appear between 4.3 and 4.4 microns. These lines indicate the presence of a higher temperature (4800 K) component, indicating simultaneous formation and reformation of CO. Such high rotational levels of CO were first seen in CasA by the new JWST spectroscopy.
4. Supernovae like Cas A, located 11,000 light-years away, occur when massive stars explode at the end of their lives, about 350 years ago. In these explosions, called core-collapse supernovae, gravity causes the star’s interior to collapse inwards when it runs out of nuclear fuel. The recoil from this collapse blasts the star’s outer shell into space, causing an explosion so bright it outshine an entire galaxy.

“It’s really surprising to see such hot CO in a young supernova remnant and indicates that CO formation is still continuing thousands of years after the explosion,” said Chris Athol, assistant professor of astronomy at Virginia Tech.

“Combining this incredible data set with previous JWST observations of supernovae will allow us to understand the pathways to molecule and dust formation in ways never before possible.”

Breakthrough imaging and spectroscopy

The observations were made using JWST’s Near Infrared Camera Instrument (NIRCam) and Mid-Infrared Instrument (MIRI), as well as detailed Near Infrared Spectrograph (NIRSpec)-Integral Field Unit (IFU) spectroscopy. The team mapped the complex structure of synchrotron radiation (light emitted when charged particles such as electrons are accelerated to high speeds in a strong magnetic field), argon-rich ejecta, and carbon monoxide (CO) molecules within Cassiopeia A. The images show an incredibly detailed and intricate pattern of shells, holes, and filaments, highlighting the power of JWST.

Seong Hyun Park, a graduate student at Seoul National University in South Korea, collaborated with Rho on modeling the CO properties.

The new observations highlight the complex and competing processes of molecular formation and destruction in supernova remnants: although CO molecules do not directly lead to dust formation, they are a key indicator of the cooling and chemical processes that ultimately lead to dust condensation.

Although this study offers a new perspective, the extent to which supernovae contribute to the formation of dust in the early universe remains a matter of debate. Researchers will continue to observe and study these phenomena to unlock the mysteries of cosmic dust and molecular formation.

The survey results are Published this week’s Astrophysical Journal Letters.