The explosion observed in the sky more than eight centuries ago probably did not completely destroy the star that produced it.
In 1181, Chinese and Japanese astronomers described a new star that remained visible for nearly six months. It was actually a supernova, but its remnant remained undiscovered for a long time. A nebula discovered much later, called Pa 30, is in the right location and has an age consistent with this historical event.
Artist’s view of the Pa 30 supernova remnant. Sulfur filaments radiate around the surviving star at the center.
Credit: W. M. Keck Observatory / Adam Makarenko.
Pa 30 has an unusual appearance. Long filaments radiate around its center, giving the whole structure a shape reminiscent of a dandelion. At its center is an extremely hot stellar object. This survivor provides a major clue: the explosion may not have completely dispersed the original star.
To examine this scenario, the researchers mapped part of the remnant in three dimensions. They used the Keck Cosmic Web Imager, installed at the Keck Observatory in Hawaii. This instrument measures light at every point and makes it possible to deduce the speed of the material from the shift in its spectral lines.
The filaments are moving at about 1,000 km/s. Most importantly, their motion remains close to free expansion: they appear to have been moving outward from the explosion without being significantly slowed down. By tracing their paths backward, the researchers obtained a date consistent with the year 1181. This strongly reinforces the identification of Pa 30 as the remnant of the historical supernova.
Composite image of the Pa 30 remnant combining X-rays from Chandra and XMM-Newton, infrared from WISE, and visible light.
Credit: NASA/CXC/U. Manitoba/C. Treyturik ; ESA ; NOIRLab/MDM/Dartmouth/R. Fesen ; NASA/JPL-Caltech.
The map also reveals a large cavity at the center of the filamentary structure. The filaments begin abruptly at a certain distance from the center, near the edge of a ring already observed in infrared. The amount of matter is also not distributed equally in all directions, a possible sign of an asymmetric explosion.
The event probably belongs to a rare category called a Type Iax supernova. In this scenario, a white dwarf undergoes a thermonuclear explosion that is less destructive than that of a typical Type Ia supernova. Part of the star may then survive. This survivor is sometimes nicknamed a “zombie star.”
Historical records point in the same direction. The 1181 supernova was less luminous than the major stellar explosions usually visible to the naked eye for months. An incomplete thermonuclear explosion could explain both this low luminosity and the current presence of a stellar remnant at the center.
One question remains: no one yet knows precisely how Pa 30’s remarkable filaments formed. A shock wave traveling back inward may have compressed matter and produced these structures. Further observations will have to determine whether this mechanism truly matches the observed geometry.