In the year 1181 CE, a celestial spectacle unfolded: a nova appeared in the constellation Cassiopeia, dazzling stargazers in China and Japan for months. This wasn’t an ordinary star, however; it was a supernova – the cataclysmic demise of a white dwarf star.
This stellar explosion occurs when the white dwarf, already incredibly dense, accretes matter from a companion star, ultimately exceeding a critical mass limit known as the Chandrasekhar limit. The result is a violent detonation, obliterating the star and leaving behind remnants that slowly expand into the vastness of space.
This particular supernova, SN 1181, remained shrouded in mystery for centuries. Its ejected material, designated Pa 30, wasn’t discovered until 2013. Then, in 2023, groundbreaking observations using the Keck Cosmic Web Imager (KCWI) revealed faint, threadlike filaments within Pa 30, connecting the ejected material to the surviving white dwarf at the center.
These filaments, resembling the spokes of a cosmic dandelion, have now been meticulously mapped, their velocity measured, providing astronomers with an unprecedented three-dimensional view of Pa 30’s ongoing expansion.
“Imagine a static image of fireworks compared to a
recording their motion as they streaked outwards from the central explosion,” explains physicist Christopher Martin of Caltech.
SN 1181, classified as a Type Ia supernova, is unusual because it left behind a zombie star—the white dwarf that survived the explosion. This type of supernova, known as Type Iax, is believed to have occurred when two white dwarfs merged, rather than through a typical mass transfer from a binary companion.
Led by astronomer Tim Cunningham
, a team of scientists at the Harvard & Smithsonian Center for Astrophysics utilized the KCWI instrument at the Keck Observatory
in Hawaii to create a detailed map of Pa 30. By analyzing the expansion of Pa 30’s material at a rate of
around 1,000 kilometers per second, the researchers confirmed the supernova’s occurrence in the year 1181.
“The material in the filaments is expanding ballistically, meaning it hasn’t been slowed down or sped up since the explosion,” says Cunningham.
The study also unveiled intriguing new
questions. Asymmetry observed in Pa 30 suggests the original supernova wasn’t uniform, and a central cavity surrounds the zombie white dwarf. The origin of these filaments, potentially formed by a reverse shock wave condensing dust, remains a puzzle.
“The morphology of this object is very strange and fascinating,” Cunningham adds.
This groundbreaking research, published in
The Astrophysical Journal Letters, offers a glimpse into the enigmatic evolution of supernova remnants, their complex motions and the mysteries that remain to be unravelled. The ghostly remnants of SN 1181 continue to captivate astronomers, reminding us of the universe’s awe-inspiring power and the enduring quest to understand its celestial phenomena.