An artist’s concept of a supernova remnant called Pa 30—the leftover remains of a supernova explosion that was witnessed from Earth in the year 1181. Unusual filaments of sulfur protrude beyond a dusty shell of ejected material. The remains of the original star that exploded, now a hot inflated star which may cool to become a white dwarf, are seen at the center of the remnant. The Keck Cosmic Web Imager (KCWI) at the W.M. Keck Observatory in Hawai‘i has mapped the strange filaments in 3-D and shown that they are flying outward at approximately 1,000 kilometers per second. (Credit: W.M. Keck Observatory/Adam Makarenko)
CAMBRIDGE, Mass. — In the year 1181 CE, Chinese and Japanese astronomers recorded a mysterious new star appearing in the night sky — a “guest star” that shone brightly for about 185 days before fading away. Now, over 840 years later, scientists have created the first detailed 3D map of the debris from this ancient stellar explosion, revealing fascinating new details about one of the rarest types of supernovae ever discovered.
The remnant of this cosmic explosion, known as Pa 30, is unlike any other supernova remnant astronomers have found. Instead of the typical cloudy, bubble-like structure, Pa 30 features striking radial filaments that stretch outward from its center like spokes on a wheel. At its heart sits an extremely hot star with surface temperatures reaching a blistering 200,000 Kelvin, nearly 35 times hotter than our Sun.
Using the powerful Keck Cosmic Web Imager on Hawaii’s Keck II telescope, researchers have now mapped out the complex three-dimensional structure and motion of these unusual filaments. Their findings, published in The Astrophysical Journal Letters, confirm that Pa 30 is indeed the remnant of the 1181 supernova and provide new insights into how this rare type of stellar explosion unfolds. Instead of completely destroying the star, this was likely a “failed” supernova that left behind a surviving stellar core.
The team’s observations revealed that the glowing filaments are expanding outward at speeds of around 1,000 kilometers per second (over 2 million miles per hour). By tracking these velocities and positions, they could effectively “rewind” the expansion back in time. Their calculations showed that all the material would have originated from a single explosion that occurred around 1181 CE – matching perfectly with historical records.
“This means that the ejected material has not been slowed down, or sped up, since the explosion,” says lead author Tim Cunningham, a NASA Hubble Fellow at the Center for Astrophysics, Harvard & Smithsonian, in a statement. “Thus, from the measured velocities, looking back in time allowed us to pinpoint the explosion to almost exactly the year 1181.”
![Lower panel: narrowband image obtained from stacking all the KCWI-red channel cubes and integrating over the wavelength range 6680–6750 Å, covering the maximally blue- and redshifted [S ii] emission features. Upper panel: the black and white image shows the [S ii] narrowband data from R. A. Fesen et al. (2023), obtained with the Hiltner telescope at Kitt Peak. Superimposed in orange and with a large transparency, we show for comparison the same KCWI-red image as in the lower panel. The zoomed-in panel shows in red the contours of the filaments in the KCWI-red image: the same filaments are detected in the two images, but the KCWI-red image is deeper, allowing the detection of fainter features](https://studyfinds.com/wp-content/uploads/2024/10/stellar-explosion.jpg)
The researchers also discovered a large cavity at the center of the remnant, surrounded by a sharp inner edge where the filaments begin. This edge lines up with a bright ring seen in infrared images, possibly marking where the blast wave from the explosion is interacting with surrounding material.
What makes this supernova particularly intriguing is that it appears to be a rare type known as a “Type Iax” – a recently discovered class that produces much weaker explosions than typical supernovae. Rather than completely obliterating the star, these failed explosions leave behind a surviving stellar remnant.
Their 3D model revealed several surprising features. The remnant contains a large central cavity surrounding the surviving star, with a sharp inner edge where the filaments begin. Additionally, the ejected material shows a notable asymmetry, with about 40% more material expelled in one direction than the other, suggesting the initial explosion itself was lopsided.
The survival of the central star offers important clues about what happened. Scientists believe the explosion began when a white dwarf – the dense, earth-sized remnant of a dead star – underwent a thermonuclear explosion. However, unlike typical supernovae that completely destroy such stars, this explosion failed to generate enough energy for complete destruction, leaving behind the ultra-hot “zombie star” we see today.
“Our first detailed 3D characterization of the velocity and spatial structure of a supernova remnant tells us a lot about a unique cosmic event that our ancestors observed centuries ago,” concludes co-author Ilaria Caiazzo, an assistant professor at the Institute of Science and Technology Austria. “But it also raises new questions and sets new challenges for astronomers to tackle next.”
Paper Summary
Methodology
The researchers used a special instrument called an integral field unit spectrograph, which allows them to collect detailed spectral data from many points across their target simultaneously. They focused on light emitted by ionized sulfur atoms in the remnant’s filaments, which appears as a distinctive pair of spectral lines. By measuring how these lines were shifted due to the Doppler effect, they could determine how fast different parts of the remnant were moving toward or away from Earth. Combined with the positions of the filaments in the sky, this gave them the full 3D structure and motion of the remnant.
Key Results
The team found that the filaments are expanding at velocities between about 500-1,400 kilometers per second, with most clustering around 1,000 kilometers per second. The overall structure is roughly spherical but contains a large central cavity. They also discovered that the filaments’ motions are almost perfectly “ballistic” – meaning they’ve been moving at constant speeds since the explosion, with very little slowing down due to interaction with surrounding material.
Study Limitations
The observations only covered about 10% of the total remnant, focusing on a radial slice extending outward from the central star. While this provided crucial information about the remnant’s structure, a complete picture would require mapping the entire object. Additionally, the researchers note that their velocity measurements have some uncertainty due to contamination from sky emission lines in a small percentage of their data points.
Discussion & Takeaways
This study provides strong confirmation that Pa 30 is indeed the remnant of SN 1181 and offers new insights into how Type Iax supernovae evolve. The nearly ballistic motion of the filaments suggests they’re expanding into a relatively low-density environment, while the asymmetry in the ejecta hints at an asymmetric explosion mechanism. The sharp inner edge of the filamentary structure, coinciding with an infrared ring, may mark the location of the reverse shock wave from the explosion.
Funding & Disclosures
The research was supported by various NASA grants, including a Hubble Fellowship grant, and received funding from the National Science Foundation. The study made use of data from NASA’s Wide-field Infrared Survey Explorer satellite and utilized the Montage software package, which is funded by the NSF. The observations were conducted using the Keck II telescope in Hawaii.
