In 1181, a new star appeared in the Cassiopeia constellation, shining brightly for six months before vanishing. Documented by Chinese and Japanese astronomers, this event, known as a "guest star," puzzled scientists for centuries. Remarkably, it is one of the few supernovae recorded before the invention of telescopes.
According to a Science report By Institute of Science and Technology Austria on Thursday, now referred to as supernova SN 1181, its remnant was traced to the Pa 30 nebula in 2021. Amateur astronomer Dana Patchick discovered this nebula in 2013 while analysing WISE telescope images as part of a citizen science project.
This nebula is unusual. At its centre lies a "zombie star," a remnant of the original explosion. The supernova likely occurred when a thermonuclear explosion ignited on a white dwarf, a dense, dead star. Typically, such an explosion would destroy the white dwarf, but in this case, part of it survived, resulting in the zombie star.
This phenomenon is classified as a Type Iax supernova. Researchers noted that strange filaments resembling dandelion petals extend from the zombie star.
Assistant Professor Ilaria Caiazzo and lead author Tim Cunningham, a NASA Hubble Fellow at the Centre for Astrophysics, Harvard & Smithsonian, recently captured detailed observations of these filaments. Their findings are published in ‘The Astrophysical Journal Letters’.
The research team used the Keck Cosmic Web Imager (KCWI) at the W. M. Keck Observatory in Hawaii. KCWI is designed to detect faint light from the universe, capturing spectral data for every pixel in an image. This technology allows researchers to measure the motion of matter in a stellar explosion, effectively creating a 3D map of the supernova remnant.
Instead of a static image, the team generated a dynamic model showing that the filaments are moving at about 1,000 kilometres per second. “The ejected material has not slowed down or sped up since the explosion,” Cunningham explained. This precise measurement allowed them to pinpoint the explosion to nearly the exact year of 1181.
The supernova's shape is also strikingly asymmetrical, indicating that this characteristic arose from the explosion itself. The filaments have a distinct inner edge, creating a gap around the zombie star.
"Our detailed 3D characterisation of this unique supernova remnant sheds light on an event observed centuries ago," Caiazzo said.
"However, it also raises new questions and challenges for astronomers." She began this project as a Burke-Sherman Fairchild Postdoctoral Fellow at Caltech before joining ISTA in May.
