Warwick astronomers are part of an international team to reveal the most detailed view yet of Pa 30, the likely remnant of a supernova documented in 1181. The new observations reveal that its famous 'firework' filaments are not smooth streaks, but chains of tiny knots.
In August 1181, Chinese, Japanese and Arabic astronomers recorded the sudden appearance of a bright new 'guest star' in the constellation now known as Cassiopeia. It stayed visible for 185 days.
More than eight centuries later, images from the Gemini North telescope on Maunakea in Hawaiʻi have revealed Pa 30, the likely remains of that explosion, in unprecedented detail. They show about ten times more filamentary structure than previously seen.
The analysis of the images, led by Dr Timothy Cunningham at the University of Warwick with international colleagues, is published in The Astrophysical Journal. It shows that the remnant's firework-shaped ejecta is made of chains of tiny gas knots rather than smooth streaks, as previously thought. This suggests thermal or density variations in the material surrounding the star shaped the ejecta as it expanded away from the explosion.
Dr Timothy Cunningham, Assistant Professor and STFC Ernest Rutherford Fellow, University of Warwick said: "These images give us the clearest picture yet of Pa 30's structure, and it's not what we expected. The filaments are made of chains of tiny knots rather than smooth streaks, providing new constraints on the nature of the space around the star before it exploded and the physical processes that have shaped the expanding ejecta. It's rare to get this level of detail on a supernova we can date to a specific week in history."
SN 1181 is one of only five supernovae in the Milky Way known to have been observed from Earth before the invention of the telescope. Eight separate texts record the sighting between 4 and 6 August 1181. At the time, the Genpei War was being fought in Japan, Henry II was on the throne of England, and the new star was even addressed in a poem to Saladin, the first sultan of Egypt and Syria.
Pa 30, a blue central star surrounded by a firework-shaped shell, is the top candidate for the supernova remnant. Surviving stars are normally 'kicked' away by a supernova explosion, but the central star of Pa 30 sits almost exactly at the centre. This implies a highly symmetrical explosion that did not send the star off course.
The findings add to evidence that SN 1181 was a rare Type Iax supernova. Unlike standard Type Ia explosions, which destroy their stars, Type Iax events are lower-energy, incomplete explosions that leave a surviving star. Pa 30 is the only known Type Iax remnant in the Milky Way.
Celestial events carried powerful meaning for medieval societies. The Bayeux Tapestry shows Halley's Comet in 1066, followed by a messenger warning King Harold II, linking the sign in the sky to his downfall. The story of the 1181 supernova is one of humans working together, across time and space, to understand the changing Universe.
