This combined image shows Pa 30, a unique stellar remnant in the constellation Cassiopeia.
Credit: NASA/CXC
It’s never too late to solve a cold case. A new paper from Syracuse University researchers proposes an explanation for both a mysterious stellar object discovered in the year 2013 and an astronomical observation first made all the way back in the year 1181.
Yes, people were keeping track of major astronomical events in the 12th century, with one in particular recorded by multiple Japanese and Chinese star-gazers in early August 1181. It was apparently visible to the naked eye and remained a “guest star” against the backdrop of stars for a full 185 days. Given its brightness, its lifetime, and the fact that it did not roam through the sky, this can only have been a supernova that occurred within the Milky Way galaxy.
In 2013, astronomers independently discovered an object they called PA 30, which had an unusual “koosh-ball” structure, with filaments extending in all directions. The researchers call this “firework morphology.” It immediately resembled an explosion frozen in time, but it was unclear how a stellar explosion could produce that particular shape.
In 2021, scientists identified PA 30 as the remnant of the 1181 supernova, called SN 1181.
SN 1181 gave rise to this unique structure, called PA 30.
Credit: Walter Scott Houston
For several years now, astronomers have believed that PA 30 is the remnant of a Type Iax supernova, the rare ‘x’ variant of the much more common Type Ia supernova. These have the unique property of not completely destroying the exploding star, leaving a so-called ‘zombie star’ behind. PA 30 has been shown to have a central zombie star as expected.
However, Type Iax supernovae are not associated with the filament structures in PA 30. What this paper proposes is that the filaments can be explained as the result of a partial supernova, one that only went through some of the steps of a full stellar explosion.
By way of an explanation, the researchers present freeze-frames of the Kingfish nuclear test detonation. They show that the nuclear detonation first looks much like PA 30, with its firework morphology—but that, just 200 milliseconds later, that structure muddied up into a chaotic cloud with no discernible structure at all.
The Kingfish explosion. Left, after 40ms. Right, after 256ms.
Credit: Syracuse University, Coughlin et al.
The new paper argues that, in SN 1181, the first phase of the supernova fizzled out and left behind an unusually active zombie star at the center. This star created abnormally strong winds of abnormally heavy elements, heavy enough to easily push around the gases expelled in the first portion of the stellar explosion.
This wind could have maintained the outward velocity and coherence of the filaments formed immediately after the explosion, prolonging the firework morphology observed in the Kingfish explosion for the better part of a millennium.
This has the intriguing implication that all supernovae might undergo a fireworks phase, but that it’s simply too short-lived to be observed.
