Gemini North reveals pearl-like knot chains in the remnant of a 1181 supernova

Chinese, Japanese and Arabic astronomers watched a supernova in Cassiopeia between 4–6 August 1181. Records say it remained visible for 185 days.

New images from the Gemini North telescope show that the debris left by that event has a far more intricate form than astronomers had thought. Pa 30, the remnant of SN 1181, lies 7,500 light-years away in Cassiopeia and appears as a blue central star surrounded by a shell shaped like a firework.

The new view is the most detailed yet captured of Pa 30. Observations with the Gemini Multi-Object Spectrograph on Gemini North, on Maunakea in Hawai'i, have resolved its fibrous structure at approximately ten times the resolution of earlier images.

Timothy Cunningham of the Harvard-Smithsonian Center for Astrophysics led the analysis of the new Gemini North observations. His team found that the radial features, once understood as smooth filaments, are chains and cascades of small gas knots.

The knots appear remarkably uniform in size. Ilaria Caiazzo of the Institute of Science and Technology Austria, who co-led the research, determined that each one is large enough to contain approximately 10 planetary system regions of the solar system, with space remaining.

Astronomers say variations in the temperature and density of matter around the exploded star may have produced the chain-like pattern as material expanded in the supernova.

The image also shows a blue-white star near the centre of the remnant, believed to be the star that remained after the explosion. Its position is almost exactly at Pa 30's centre, an unusual arrangement because surviving stars are almost always displaced from the geometric centre after a supernova.

SN 1181 is one of only five supernova remnants in the Milky Way that were seen in the sky before the invention of the telescope. Yet Pa 30 itself was unidentified until 2013, when the American amateur astronomer Dana Patchick found it through a citizen science project searching for planetary nebulae in data from the Wide-field Infrared Survey Explorer space telescope.

It was Patchick's 30th nebula discovery, giving Pa 30 its designation.

The explosion that made Pa 30 is believed to have been a rare Iax-type supernova, and Pa 30 is currently the only known Iax-type supernova remnant in the Milky Way. In standard Ia-type explosions involving white dwarfs in binary star systems, the explosion's energy destroys the white dwarf. An Iax-type explosion has lower energy, allowing the star to survive.

The findings were published in The Astrophysical Journal and give astronomers a closer view of how material from this unusual type of explosion was dispersed.