The strange star left by the supernova of the year 1181

In 1181, a new star shone near the Cassiopeia constellation for six months before disappearing. This event was recorded by Chinese and Japanese observers as the appearance of a “guest star.” And it has baffled astronomers for centuries.

1181 is one of the few supernovae documented before the invention of telescopes. Furthermore, it was the one that remained the longest without being able to relate it to any of the celestial objects visible today. Now known as the supernova SN 1181, its remnant (the remains of the explosion) was only identified in 2021, corresponding to the Pa 30 nebula, found in 2013 by amateur astronomer Dana Patchick while examining an archive of images from the WISE space telescope. as part of a citizen science project. Citizen science is called research that is nourished by the free collaboration of volunteers, without requiring them to have technical training, to help scientists with simple but time-consuming tasks.

However, far from the mystery disappearing, one enigma was replaced by another: this nebula is not the typical supernova remnant. In fact, astronomers were intrigued to find in the center of the remnant an object that they could only describe as a “zombie star.” It is not a neutron star nor is it a black hole.

But then what is it?

Supernova 1181 is believed to have occurred when a thermonuclear explosion occurred in a dense, dead star, the type known as a white dwarf. Normally, the white dwarf is completely destroyed in this type of explosion, but in this case, part of the star survived. This star fragment is a kind of “zombie star.”

This type of unusual partial explosion is called a type Iax supernova.

Another enigma is that strange filaments emanate from this zombie star, somewhat reminiscent of the petals of a dandelion flower.

Artist’s recreation of the supernova remnant called Pa 30, the collection of debris from the supernova explosion seen from Earth in the year 1181. Unusual filaments protrude from a dusty layer of ejecta. At the center of the remnant resides an object that is neither a normal star, nor a neutron star, nor a black hole. It is a hot, swollen star, dubbed a “zombie star,” that could cool down to become a white dwarf again. (Image: WM Keck Observatory / Adam Makarenko)

Now, using the KCWI spectrograph that the California Institute of Technology (Caltech) has installed at the WM Keck observatory in Hawaii, United States, scientists have managed to delve deeper into the structure of these strange filaments.

The team includes, among others, Ilaria Caiazzo and Tim Cunningham, both from the Austrian Institute of Science and Technology.

The authors of the study have managed to create a detailed 3D map of the nebula and its enigmatic filaments.

In addition, they have found out that the material in the filaments travels at about 1,000 kilometers per second.

The general shape of the supernova, apart from the dandelion-shaped filaments, is another puzzle. The team has found that the set of material within the filaments that is being expelled away from the explosion site is unusually asymmetric. This suggests that the asymmetry has its origin in the initial explosion itself.

Although some things about the supernova of the year 1181 are now better known thanks to this study, others remain enigmas and more research will be needed to clarify them.

The study is titled “Expansion properties of the young supernova type Iax remnant Pa 30 revealed.” And it has been published in the academic journal The Astrophysical Journal Letters. (Fountain: NCYT by Amazings)