In 1181, a bright “guest star” appeared near the Cassiopeia constellation, shining for six months before fading away.
Ancient Chinese and Japanese observers recorded this event, which has puzzled astronomers for centuries.
Known as supernova SN 1181, this explosion remained an “orphan” because, for a long time, no known celestial object could be connected to it.
This mystery was partly solved in 2021 when scientists linked the ancient event to a nebula called Pa 30.
The nebula was first discovered in 2013 by an amateur astronomer named Dana Patchick, who was working on a citizen science project using images from NASA’s WISE telescope.
However, Pa 30 is no ordinary supernova remnant. At its center lies a surviving piece of the exploded star—a rare “zombie star.”
The supernova responsible for creating Pa 30 is thought to have been a Type Iax supernova.
In these rare cases, a dense, dead star called a white dwarf explodes, but not completely. Some parts of the white dwarf survive, forming what astronomers call a “zombie star.”
What makes SN 1181 even more unusual is that strange filament-like structures extend outward from the zombie star, resembling the petals of a dandelion.
A team led by Assistant Professor Ilaria Caiazzo and NASA Hubble Fellow Tim Cunningham studied these filaments closely using the Keck Cosmic Web Imager (KCWI) at the W. M. Keck Observatory in Hawaii.
The KCWI is an advanced instrument that captures faint light and can measure how matter moves in space, creating a detailed 3D image of the supernova remnant.
Thanks to KCWI, the researchers could map the supernova remnant and see how the material in the filaments was moving. They discovered that the filaments expanded at a high speed of around 1,000 kilometers per second.
The team’s measurements showed that the material hasn’t slowed down or sped up since the explosion, allowing them to trace the event back almost precisely to the year 1181.
Beyond the dandelion-like shape, the researchers noticed something unusual about the supernova remnant.
The ejecta, or the material thrown out by the explosion, is asymmetrical, meaning that the explosion wasn’t evenly spread out. They also found a sharp inner edge around the zombie star, creating a noticeable gap.
Caiazzo explained that this first detailed 3D study of the supernova remnant tells us a lot about a unique cosmic event witnessed nearly a thousand years ago.
But she added that it also raises new questions, giving astronomers fresh challenges to explore in the future.
Source: KSR.
