Observations of the youngest supernova in the Milky Way with its core collapse provide information about the conditions that lead to the formation and destruction of molecules and dust within the supernova erupting.

The SETI Institute has announced the latest findings from the James Webb Space Telescope (JWST) on the supernova remnant Cassiopeia A (Cas A). These observations of the youngest known collapsed supernova in the Milky Way provide insight into the conditions that lead to the formation and destruction of molecules and dust within supernova emissions. The results of the study change our understanding of dust formation in the early Universe in galaxies detected by JWST 300 million years after the Big Bang.

“Researchers believe that supernovae like those that formed Cas A are vital sources of the dust seen in distant, high-redshift galaxies. These new ideas challenge the belief that the dust originates primarily from intermediate-mass stars in the asymptotic giant branch (AGB) of the sinusoidal patterns of CO fundamental vibration lines in modern galaxies,” said Dr. Jeonghee Roh, a senior scientist at SETI, the institute that led the research. “The patterns appear to have been artificially created.”

Key findings include:

1. CO molecular formation: Data show that there is more CO gas than argon gas in the outer layers, suggesting that CO molecules reformed after the recoil. This data is important for understanding how cooling and dust formation occur after a supernova explosion. The images show that CO molecules reformed on impact and may have preserved the dust in the ejected material.
2. Detailed spectroscopy: NIRSpec-IFU spectra of two major regions in Cas A show differences in the formation of the elements. Both regions have strong signals from CO gas and various ionized elements such as argon, silicon, calcium, and magnesium. The CO baselines are sinusoidal structures of dozens of CO main vibration lines with a continuum beneath them due to the high speed of the CO molecules.
3. Temperature data: The study suggests a temperature of around 1080 K based on CO2 emissions. This helps us understand how dust, molecules, and highly ionized gas interact in supernovas. But the authors also find vibration lines in high-spin (J=90) lines, with signatures appearing between 4.3 and 4.4 μm. These lines indicate the presence of a higher temperature component (4800 K), implying that CO was formed and reformed simultaneously. CO from such high spin levels is seen for the first time in Cas A with the new JWST spectroscopy.
4. Supernovas like Cas A, located 11,000 light-years away, are explosions that occurred about 350 years ago when a massive star reached the end of its life. Called a collapse supernova, the interior of a star collapses inward under the influence of gravity when the nuclear fuel that powers the star runs out. The recoil from this collapse blows the star’s outer shell into space in an explosion that can darken an entire galaxy.

“Seeing such hot carbon dioxide in a young supernova remnant is truly remarkable and suggests that carbon dioxide formation is still occurring hundreds of years after the explosion,” said Chris Eshall, an assistant professor at Virginia Tech. “Combining this impressive dataset with previous JWST supernova observations will allow us to understand the pathways leading to molecules and dust formation in a way that has not been possible before.”

Innovative imaging and spectroscopy

The observations used JWST’s Near Infrared Camera (NIRCam) and Mid Infrared Instrument (MIRI), as well as the Detailed Near Infrared Spectrograph with Integral Field Units (IFU) (NIRSpec). The team imaged complex patterns of synchrotron radiation (light emitted when charged particles such as electrons are accelerated to high speeds in strong magnetic fields), argon-rich emissions, and carbon monoxide (CO) molecules in Cas A. The complex patterns of shells, holes, and filaments underscore JWST’s power, said Song Hyun Park, a graduate student at Seoul National University in South Korea who performed simulations of CO properties with Roh.

The new observations highlight the complex and competing processes behind the formation and destruction of supernova molecules. While CO molecules do not directly lead to dust formation, they are critical indicators of the cooling and chemical processes that ultimately lead to dust condensation.

Although this research provides new information, there is an ongoing debate about the extent to which supernovas contribute to dust formation in the early universe. Researchers will continue to investigate these events with future observations and studies to unravel the mysteries of cosmic dust and molecular formation.