New research led by University of Hong Kong astronomers shows that a fast expanding nebula called Pa 30 surrounding the hot Wolf-Rayet star IRAS 00500+6713 fits the profile, location and age of the ‘Guest Star’ of 1181 CE.
(a) WISE false color image of the Pa 30 nebula where blue and green stand for 11 μm emission, and red for 22 μm; (b) in this false color image, where green stands for WISE 11 μm (as in the left panel) and red for WISE 22 μm (adjusted to show extended emission), the emission from the central star is highlighted in blue from the GALEX near-UV data, while the XMM-Newton contors show that the majority of the X-ray emission originates from the core of the nebula; a background point source is seen westward of the CS in the XMM-Newton contour map; (c) the 2.1 m KPNO image; the green cross in the center of the image marks the location of the CS; panels (a)-(c) are reproduced at the same angular scale and orientation; at the Gaia distance of Pa 30 of 2,300 parsecs, an angular scale of 45” translates to about 100,000 AU. Image credit: Ritter et al., doi: 10.3847/2041-8213/ac2253.
Only nine historically recorded supernova explosions are known in our Milky Way Galaxy.
In only five cases has the remnant of the supernova been identified. For the other cases, the remnant is not known with certainty.
Of these, SN 1181 was originally seen and documented by Chinese and Japanese astronomers.
It was as ‘bright as the planet Saturn’ and remained visible for 185 days from August 6, 1181 to February 6, 1182.
The ancient astronomers also recorded an approximate location in the sky of the sighting.
“The remnant is crucial for identifying the type of supernova, while the known time of the explosion and duration constrain the models of the evolution of the remnant,” said University of Manchester’s Professor Albert Zijlstra and colleagues.
In the study, the astronomers found that the Pa 30 nebula is expanding at an extreme velocity of more than 1,100 km per second.
They used this velocity to derive an age at around 1,000 years, which would coincide with the events of 1181 CE.
“The historical reports place the guest star between two Chinese constellations, Chuanshe and Huagai. IRAS 00500+6713 (dubbed Parker’s star) fits the position well,” Professor Zijlstra said.
“That means both the age and location fit with the events of 1181.”
Pa 30 and IRAS 00500+6713 have previously been proposed as the result of a merger of two white dwarfs.
Such events are thought to lead to a rare and relatively faint type of supernova, called a Type Iax supernova.
“Only around 10% of supernovae are of this type and they are not well understood. The fact that SN 1181 was faint but faded very slowly fits this type,” Professor Zijlstra said.
“It is the only such event where we can study both the remnant nebula and the merged star, and also have a description of the explosion itself.”
The merging of remnant stars, white dwarfs and neutron stars, give rise to extreme nuclear reactions and form heavy, highly neutron-rich elements such as gold and platinum.
“Combining all this information such as the age, location, event brightness and historically recorded 185-day duration, indicates that Parker’s star and Pa 30 are the counterparts of SN 1181,” Professor Zijlstra said.
“This is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible. It is nice to be able to solve both a historical and an astronomical mystery.”
The team’s work was published in the Astrophysical Journal Letters.
Andreas Ritter et al. 2021. The Remnant and Origin of the Historical Supernova 1181 AD. ApJL 918, L33; doi: 10.3847/2041-8213/ac2253