Unveiling the physics of molecular formation in supernova remnant of SN 1987A

Published: 1st Feb, 2024, Academia Sinica, Institute of Astronomy & Astrophysics (ASIAA), Taiwan

 Dr. Masaomi Ono from the Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA) led an international team to investigate the molecular formation in  Supernova 1987A  (SN 1987A) and obtain research results that will appear in the coming  issue of the Astrophysical Journal Supplement.

Massive stars, culminating in explosive events known as supernovae, generate some of the universe's most powerful explosions. The aftermath of these explosions forms supernova remnants, playing a crucial role in connecting the life cycle of massive stars to the broader interstellar medium  within galaxies.

Supernova 1987A, discovered in the Large Magellanic Cloud in February 1987, offers a unique opportunity to study the evolution from a core-collapse supernova to a supernova remnant due to its proximity and youth. Recent breakthrough observations of SN 1987A by the Atacama Large Millimeter/submillimeter Array (ALMA) have unveiled 3D distributions of diatomic molecules, specifically carbon monoxide (CO) and silicon monoxide (SiO), newly formed in the ejecta. An intriguing feature is the iconic ring-like distribution of carbon monoxide. This highly non-spherical molecular distribution holds promise for shedding light on the explosion mechanism, progenitor star properties, and the formation of molecules in the ejecta—areas that remain poorly understood.

Motivated by these observations,  the research team  harnessed the power of supercomputers to conduct chemical reaction calculations based on 3D hydrodynamical simulations of asymmetric core-collapse supernova explosions, including one resulting from a binary merger process. They focused on understanding the impact of matter mixing during the supernova shock propagation inside the star. Their findings indicate that the highly non-spherical, asymmetric, bipolar-like explosion and the density structure of the progenitor star, a compact blue supergiant, contribute to the formation of molecules, particularly CO and SiO. This occurs through complex physical processes such as gas heating, ionization, and dissociation of molecules driven by the radioactive decay of 56Ni. The calculated distribution of CO aligns qualitatively with the observed ring-like distribution by ALMA. 

Dr. Shigehiro Nagataki, a chief scientist at Riken, stated, "We have performed the world's first simulation of molecular formation based on a 3-D supernova explosion. Our results will be compared with various observations of SN 1987A, including JWST, to provide new insights into the explosion mechanism of core-collapse supernovae." Dr. Masaomi Ono, the lead author of the paper, added, "The characteristic distribution of the seed atoms and radioactive 56Ni could affect the amounts and distribution of molecules, in particular carbon monoxide and silicon monoxide." Dr. Ke-Jung Chen supported this discovery, stating, "This research demonstrates the importance of ejecta mixing in the molecular and dust formation inside young supernova remnants."

The James Webb Space Telescope (JWST) has begun the study of one of the most renowned supernovae, SN 1987A. Located 168,000 light-years away in the Large Magellanic Cloud, SN 1987A has been a target of intense observations at wavelengths ranging from gamma rays to radio for nearly 40 years, since its discovery in February of 1987. New observations by NIRCam (Near-Infrared Camera) on JWST provide a crucial clue to our understanding of how a supernova develops over time to shape its remnant. Image Credit: NASA, ESA, CSA, M. Matsuura (Cardiff University), R. Arendt (NASA’s Goddard Spaceflight Center & University of Maryland, Baltimore County), C. Fransson (Stockholm University), J. Larsson (KTH Royal Institute of Technology), A. Pagan (STScI)

Distribution of representative elements, 56Ni, 28Si, 16O, and 12C, before starting the formation of molecules (corresponding to the seed atoms, iron, silicon, oxygen, and carbon, respectively). The +Z (−Z) direction is the stronger　(weaker) bipolar-like explosion axis. The +Y direction is perpendicular to the bipolar explosion axis. Image Credit: Masaomi Ono/ASIAA

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