Astronomers’ best view yet of the aftermath of a “guest star” supernova seen in 12th-century China and Japan has revealed one of the strangest objects in the heavens. It consists of hundreds of spectacular filaments of gas and dust arranged like the seeds of a dandelion around a “zombie” white dwarf.
Such white dwarf stars are the hot, glowing stellar cores left behind when dying sunlike stars blow off their outer layers.
This one—called “Parker’s Star,” the remnant of the supernova SN 1181, named for the year it appeared in Earth’s skies—lies about 8,000 light-years from our solar system, near the northern constellation of Cassiopeia. And it’s nestled within a geometric spray of ejected material known as the planetary nebula Pa 30.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Scientists can’t yet explain the nebula’s eye-catching shape, but a new study has revealed hidden details of its formation, and researchers now hope to learn more about the mysterious thermonuclear processes that caused it.
“It’s absolutely amazing,” says study lead author Tim Cunningham, a research fellow at the Center for Astrophysics | Harvard & Smithsonian. “It has really captured the imagination of many international groups of astronomers.”
A Resurrected Mystery
Although the nebula was discovered in 2013 and its central star described in 2019, the object wasn’t recognized until 2021 as the remnant of the supernova witnessed in 1181.
Historical accounts indicate the “guest star” was visible for 185 days, flaring to become as bright as Saturn where no star had been seen before. But after the celestial outburst faded from view, its exact location was lost for centuries.
Multiple enigmas accompanied its rediscovery a few years ago. Besides its curious dandelion-shaped nebula, the white dwarf’s very existence is a conundrum: such stars normally don’t survive a supernova’s blast, making this one a rare member of the stellar undead—a so-called zombie star.
Most supernovae happen when massive stars run out of fuel and collapse under their own weight.
But sometimes they occur by other mechanisms, explains study co-author Ilaria Caiazzo, an astrophysicist at the Institute of Science and Technology Austria. One variety, known as type Ia, happens when a white dwarf star merges with another white dwarf or strips gas from a companion star. In either case, that additional material pushes the star over a critical threshold, causing a mind-numbingly massive thermonuclear explosion that destroys the star.
Because the amount of detonating material is roughly the same for every type Ia supernova, these cosmic cataclysms all shine with a similar brightness and can be seen far beyond their host galaxy. This allows astronomers to use them as “standard candles” to estimate vast cosmic distances.
The supernova seen in 1181, however, was an even rarer type Iax supernova, in which part of the central white dwarf star somehow survives—although just why isn’t yet known, Caiazzo says.
To date, astronomers have found the remnants of tens of thousands of “regular” supernovae and more than a thousand type Ia supernovae. But less than a hundred type Iax supernova remnants are known—and this is the only one found in our galaxy.
“This remnant allows us to study the evolution of the central star and of the ejecta, about 1,000 years after the explosion and in our own backyard,” she says.
A Skewed Supernova?
Cunningham, Caiazzo and their colleagues used the Keck Cosmic Web Imager (KCWI), a spectrograph attached to one of telescopes at the W.M. Keck Observatory, near the summit of Mauna Kea in Hawaii. Spectrographs are workhorses of astronomy that split light into its constituent wavelengths, or colors, allowing observers to discern the chemical compositions and even the subtle motions of cosmic structures.
KCWI’s sharp spectral eyes allowed the team to create a precise three-dimensional map of part of the strange supernova remnant and its filaments, which are now about three light-years long. The data show that the filaments are moving at about 1,000 kilometers per second—a speed they’ve apparently held ever since the supernova occurred, a little more than 840 years ago.
The gas and dust ejected by supernovae typically moves much faster—tens of thousands of kilometers each second—and the “zombie” white dwarf at the center of the nebula is also emitting powerful stellar winds.
But Cunningham says that, against expectations, these stellar winds seem not to be significantly sculpting the filaments.
Instead the filaments may have arisen from the interaction of ejected gas and dust with the “reverse shock” caused by the supernova blast colliding with the interstellar medium.
Caiazzo adds that this process could also explain the sharp “inner edge” of the dandelion nebula as a space filled with ejected gas and dust that has yet to condense and become part of the dense filaments.
The researchers also saw hints of an asymmetry in the explosion, with more filaments pointing away from Earth than pointing toward it.
It’s unclear if this tantalizing potential asymmetry will be validated in follow-up studies of the nebula, but if real, it may help explain how the central white dwarf managed to survive the supernova partially intact, Cunningham says.
Parker’s Star
The strange star caught the attention of University of Hong Kong astronomer and astrophysicist Quentin Parker, who wasn’t involved in the latest study but who co-authored research papers about the star in 2021 and 2023.
The 2021 paper was the first to link the nebula and remnant with the 1181 supernova, dubbing the object “Parker’s Star.”
Parker has now discovered more than 1,000 planetary nebulae—more than anyone else in history.
But he’d never put his own name on any of them before this one.
“This object is going to be a gold mine to study,” he says. “I’m not surprised a lot of other people are studying it, because it is so fascinating and so unique.”