The star that exploded in 1181 left gas knots 10 times wider than Neptune’s orbit

The glowing streaks that burst out of Pa 30 like a frozen firework are not streaks at all. New images from the Gemini North telescope in Hawaii show that each filament is a chain of gas knots strung like pearls, and every knot is wide enough to hold the orbits of all eight planets about ten times over.

That matters because Pa 30 is the only place in our galaxy where astronomers can study the debris of a rare, half-failed kind of stellar explosion with the survivor still sitting inside it. The knots are the first close look at how that debris broke apart, and the star’s position says the blast was far more even than most supernovae.

Pa 30 is the likely leftover of a “guest star” that astronomers in medieval China and Japan, along with Arabic sources, watched blaze in the constellation Cassiopeia. Today the nebula looks like a dandelion seed head: a sphere of radial filaments around an extremely hot central star. The new observations, led by Tim Cunningham of the Center for Astrophysics | Harvard & Smithsonian and Ilaria Caiazzo of the Institute of Science and Technology Austria (ISTA), reveal roughly ten times more of those filaments than any earlier image.

“The planetary region of our solar system could fit in each knot about ten times with room to spare,” Caiazzo said. “The knots are quite strikingly uniform. We are excited to try to model them.”

How Gemini North pulled the knots out of the starlight

The team used the Gemini Multi-Object Spectrograph (GMOS) on Gemini North, which sits more than 4,200 meters up on Maunakea. Instead of collecting all visible light, they used narrowband filters that let through only the glow of specific atoms: ionized sulfur, which shines red, and doubly ionized oxygen, which shines blue-green. Blocking everything else makes faint gas stand out against the crowded star field behind it.

In sulfur light, the number of detected filaments rose by about an order of magnitude compared with previous studies. Looked at closely, those filaments were not smooth lines but cascades of knots or clumps. The oxygen images delivered a second result: the first confirmation that the diffuse oxygen glow seen in earlier observations comes from the same filaments as the sulfur, not from a separate cloud.

Measuring the knots meant working at the edge of what the atmosphere allows. The median width of a sulfur filament came out at 0.7 arcseconds, only slightly broader than the 0.5 arcsecond blur of the air above the telescope that night. That small excess means the filaments are partly resolved, and it implies a typical knot diameter of about 10^16 centimeters, or roughly 100 billion kilometers.

Pa 30 in numbers you can feel

Neptune’s orbit is about 9 billion kilometers across, so a single knot in Pa 30 spans more than ten of them laid side by side. That is roughly 670 times the distance between Earth and the Sun, and the nebula is threaded with chains of these knots.

Pa 30 sits about 7,500 light-years from Earth. That sounds remote, but it is far closer than the center of the Milky Way, about 26,000 light-years away, and that proximity is the whole reason the knots can be seen. “We can see this much detail because of Pa 30’s proximity to Earth,” Caiazzo said.

The star at the heart of the nebula, catalogued as IRAS 00500+6713, burns at about 200,000 degrees Celsius, more than 30 times hotter than the surface of the Sun. It drives a wind of about 16,000 kilometers per second, over 5 percent of the speed of light. The supernova that made it is one of only five in the Milky Way observed from Earth before the telescope was invented.

The star that never got kicked

Most supernovae destroy their star or leave a compact corpse behind. Pa 30 belongs to a rarer class called Type Iax: lower-energy, incomplete thermonuclear explosions that leave a battered survivor, nicknamed a “zombie star.” Researchers have proposed that this one began as a collision between two white dwarfs, the dense, Earth-sized remains of stars that have used up their fuel. Pa 30 is the only known Type Iax remnant in the Milky Way. A few similar objects exist in other galaxies, but this is the only one where telescopes can see the survivor.

In lopsided explosions, the surviving star gets a “kick” that sends it drifting away from the center of its debris. The Gemini images put the nebula’s center right where the star is. The team set an upper limit of about 100 kilometers per second on any sideways kick, tiny next to the star’s own wind.

“Explosions conserve momentum. If the explosion itself was perfectly symmetric, the ejecta should also be symmetric, and the surviving star should not receive a substantial kick,” Caiazzo said. “We practically don’t see the star moving away at all.”

What the knots don’t settle

The images show the knots but not what made them. The researchers suggest that variations in temperature or density in the gas around the star may have broken the outflowing debris into clumps, but no model has yet reproduced chains this regular. Caiazzo’s own description, strikingly uniform and waiting to be modeled, is an open question rather than an answer.

The size measurement also leans on a small margin. The filaments are only slightly wider than the atmospheric blur, so the knot diameter is an inference from partly resolved profiles, not a clean measurement of individual knots. The oxygen images were taken in poorer conditions, with widths of about 1 arcsecond that match the blur itself.

The kick limit applies only to motion across the sky. Images cannot measure movement toward or away from us, and an earlier study by the same group with the Keck Cosmic Web Imager found more debris on one side than the other along our line of sight, which they said might hint at an asymmetric explosion. Squaring that with a star that has barely moved sideways is part of the unfinished work. Even the link to the historical supernova rests on age, position and brightness that fit, not on a direct signature.

From guest star to Pa 30

According to NOIRLab, eight separate texts record the event. Observers first noted the new star between 4 and 6 August 1181, and it stayed visible in Cassiopeia for 185 days. For decades astronomers tied it to a remnant called 3C 58, but that object’s estimated age never fit comfortably.

Pa 30 itself turned up only in 2013, when amateur astronomer Dana Patchick spotted it in infrared data from NASA’s Wide-field Infrared Survey Explorer during a citizen-science search for planetary nebulae. It was the 30th nebula he found. In 2021 a team led by Andreas Ritter measured a shock moving at about 1,100 kilometers per second and an expansion age of roughly 1,000 years, with a sky position within 3.5 degrees of the Chinese and Japanese reports. In 2024, Cunningham and Caiazzo used the Keck Cosmic Web Imager to show the debris is coasting outward almost freely, which they called strong confirmation that the nebula comes from the 1181 event.

“Reliable historical records of stellar explosions extend back only about a thousand years. For all we know, there might well be similar remnants still lurking in the dark in our own galaxy,” Cunningham said.

Common questions about Pa 30 and the supernova of 1181

What is Pa 30?

Pa 30 is a nebula in the constellation Cassiopeia, about 7,500 light-years away, made of radial filaments of gas around a very hot surviving star. It is the likely remnant of the supernova that Chinese, Japanese and Arabic sources recorded in 1181.

Can you see the supernova of 1181 today?

Not with the naked eye. The explosion faded after about six months, and its remnant Pa 30 is faint enough that it was only identified in 2013 in infrared survey data. Its filaments show up only in deep images from large telescopes such as Gemini North.

What is a Type Iax supernova?

It is a weaker, incomplete version of the thermonuclear explosions that destroy white dwarfs. Instead of blowing the star apart completely, it leaves a damaged survivor, often called a zombie star. Pa 30 is the only known remnant of this type in the Milky Way.

How big are the knots in Pa 30?

The paper estimates a typical knot diameter of about 10^16 centimeters, roughly 100 billion kilometers. According to the team, the region of our solar system that holds the planets would fit inside each knot about ten times.

What comes next

The team now wants to model how such regular chains of knots formed. They also plan to use Pa 30’s distinctive features as a template to search the Milky Way and nearby galaxies for similar remnants. “Astronomy has entered the big data era,” Cunningham said. “Our findings will help us screen through the enormous datasets.” The study was published on 6 October 2026 in The Astrophysical Journal.

Reference: Cunningham et al., “Detection of Knots in the Type Iax Supernova Remnant Pa 30,” The Astrophysical Journal, 2026. DOI: 10.3847/1538-4357/ae9cb2

Tags: astronomy, Supernova, Gemini North, NOIRLab, Pa 30, SN 1181