Supernova Dust Formation Challenged by Early Universe Observations

The SETI Institute released the most recent observations of Cassiopeia A (Cas A), a supernova remnant, obtained by the James Webb Space Telescope (JWST). These studies of the Milky Way's youngest known core-collapse supernova shed light on the circumstances surrounding the creation and devastation of dust and molecules in supernova ejecta.

The results of the study modify the notion of how dust formed in the early cosmos in the galaxies that JWST observed 300 million years after the Big Bang. Supernovae, like the one that created Cas A, are considered important generators of the dust visible in far-off, high-redshift galaxies.

These new findings cast doubt on the notion that the majority of dust in modern galaxies originates from intermediate-mass stars on the asymptotic giant branch (AGB).

It is remarkable to see how bright the carbon monoxide emission detected in JWST NIR imaging and spectroscopy, showing a few tens of sinusoidal patterns of CO fundamental rovibrational lines. The patterns look like they were artificially generated.

Dr. Jeonghee Rho, Senior Research Scientist, SETI Institute

Key Findings Include:

• Molecular CO Formation: The data indicates that after the reverse shock, CO molecules are again forming because there is more CO gas than argon gas in the outer layers. Understanding cooling and dust generation following a supernova explosion depends on these data. CO molecules are shown in the photos to have reassembled behind the shock, which may have shielded the dust in the ejecta.
• Detailed Spectroscopy: Two important regions in Cas A's NIRSpec-IFU spectra reveal variations in the elemental formation process. Both areas exhibit a variety of ionized elements, including argon, silicon, calcium, and magnesium, as well as strong CO gas indications. Due to the fast velocity of the CO molecules, the fundamental CO lines are a few tens of sinusoidal patterns of CO fundamental vibrational lines with a continuum-like beneath.
• Temperature Insights: According to the study, the temperature is roughly 1080 K based on CO gas emissions. This aids in comprehending the interactions between highly ionized gas, dust, and molecules in supernovae. Nevertheless, the authors also found high rotational (J = 90) lines, whose features appear between 4.3 and 4.4 µm, have vibrational lines. These lines suggest the simultaneous synthesis and reformation of CO because they show the presence of a hotter temperature component (4800 K). Using the new JWST spectroscopy, CO from such high rotational levels is first observed in Cas A.
• Explosions known as supernovae, like the 11,000 light-year-away Cas A, happen when a high-mass star dies some 350 years ago. When the nuclear fuel that drove the star runs out, the star's interior collapses inwards, a phenomenon known as a core-collapse supernova. An explosion that can outshine an entire galaxy occurs as the star's outer shell is blasted into space by the collapse's rebound.

To see such hot CO in a young supernova remnant is truly remarkable and indicates that CO formation is still happening hundreds of years after the explosion. Combining such impressive data sets with earlier JWST observations of supernovae will allow us to understand the pathway to molecules and dust formation in a way not previously possible.

Chris Ashall, Assistant Professor, Virginia Tech

Groundbreaking Images and Spectroscopy

In addition to precise Near-Infrared Spectrograph (NIRSpec)-Integral Field Units (IFU) spectroscopy, the observations made use of JWST's Near Infrared Camera Instrument (NIRCam) and the Mid Infrared Instrument (MIRI).

The group mapped the complex architectures of argon-rich ejecta, carbon monoxide (CO) molecules, and synchrotron radiation light released when charged particles, such as electrons, are accelerated to high speeds in strong magnetic fields.

The photographs demonstrate the capability of JWST by displaying incredibly intricate and detailed patterns of shells, holes, and filaments.

Alongside Rho, a graduate student at Seoul National University in South Korea named Seong Hyun Park modeled the CO characteristics.

The new findings shed light on the intricate and competitive processes involved in producing and destroying molecules in supernova remnants. CO molecules are essential markers of the cooling and chemical reactions that finally result in dust condensation, even though they do not directly cause dust creation.

The question of how much supernovae contribute to dust production in the early cosmos is still debatable, even though this study provides fresh insights. To solve the riddles of cosmic dust and molecule formation, researchers will continue to examine these events through additional observations and studies.

Journal Reference:

Rho, J., et al. (2024) Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST. Astrophysical Journal Letters. doi.org/10.3847/2041-8213/ad5186.