Almost a millennium ago, Chinese and Japanese astronomers recorded a mysterious new star, only for it to disappear from the night sky after six months.
In 1181, near the Cassiopeia constellation, this “guest star” became visible. Known today as supernova SN 1181, this “zombie star” has remained a scientific curiosity for centuries and has recently resurfaced as a subject of interest for entirely new reasons.
For years, the star was considered lost to time, with no visible celestial objects in the modern sky correlating to SN 1181. That changed when scientists reexamined work from 2013 by Dana Patchik, a citizen scientist. While combing through data from the WISE telescope, Patchik, an amateur astronomer, discovered the Pa 30 Supernova Remnant. In 2021, researchers linked this discovery to the lost SN 1181.
Pa 30: The Remnant of Star Birth
What makes Pa 30 especially unusual is that a “zombie star” resides at its core. This star is all that remains of an ancient thermonuclear explosion, which is believed to have produced the SN 1181 event. The explosion is hypothesized to have occurred on a white dwarf—a dead star that would typically be obliterated in such an event. Yet, somehow, a “zombie” remnant persists at Pa 30’s core. The technical term for this kind of event is a “Type Iax supernova.”
The mystery of this cosmic revenant deepens, however. In 2023, scientists observed strange filaments emerging from the remnant. Researchers are now investigating these outgrowths, leading to the first close-up observations of these peculiar structures.
Studying Outgrowths of a Zombie Star
Lead author Tim Cunningham from Harvard and the Smithsonian is collaborating with ISTA Assistant Professor Ilaria Caiazzo and Caltech Professor Christopher Martin to lead the research. Their primary tool is the Keck Cosmic Web Imager (KCWI), operated by Caltech and constructed under Martin’s supervision. KCWI, located near the summit of Mauna Kea in Hawaii, is sensitive enough to capture some of the faintest light sources in the universe. Its sensitivity allows it to gather infrared spectral information from every pixel, measuring motion in distant stellar explosions. These capabilities let researchers examine light shifts, similar to the Doppler effect, and record complex 3D data.
This 3D mapping ability allowed the team to understand the phenomenon at a depth previously inaccessible. Traditional imaging would capture only the chaotic ignition of a supernova. The 3D model, however, maps the nebula and its unusual filaments, revealing that the ejected material travels at 1,000 kilometers per second. Even more intriguing, the ejecta appears asymmetrical, with a gap between the zombie star’s surface and the start of the filaments.
“We find the material in the filaments is expanding ballistically,” said Cunningham. “This means that the material has not been slowed down nor sped up since the explosion. From the measured velocities, looking back in time, you can pinpoint the explosion to almost exactly the year 1181.”
Room for Future Research
The team still has many questions they hope to address in future studies. Their efforts will include detailed observations and further theoretical work. Higher-resolution infrared images and spectroscopy could help answer lingering questions, such as whether the emissions consist of dust or hot gas.
“These questions can probably only be answered by a space-based infrared telescope like the James Webb Space Telescope,” said Cunningham. “From the optical spectroscopy side, we would like to observe more of the nebula with KCWI to investigate whether the asymmetry in ejected material along the line of sight persists across the nebula or not. On the theoretical side, we would also like to help develop numerical models to try to understand the formation mechanism for these filaments.”
The recent paper, “Expansion Properties of the Young Supernova Type Iax Remnant Pa 30 Revealed” was published on October 24, 2024, in The Astrophysical Journal Letters.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.