According to CNN, the supernova, named “SN 1181”, is one of several supernovas that date back to the time before the invention of the telescope and is referred to as a “guest star” in Chinese and Japanese historical records because it appeared temporarily.
In their research, astronomers created a computer model of the evolution of the supernova, which is 7,000 light-years away from Earth, from the initial explosion to the present day.
The team compared the model with archive telescopic observations of the nebula, a giant cloud of gas and dust that is still visible, and found that SN 1181 is a rare Type Iax thermonuclear explosion caused by the collision of two white dwarf stars.
“SN 1181” is the only example in the Milky Way Galaxy
“Type Iax” supernovas are a rare type of supernova called “Type Ia” that occur in binary star systems. They are weaker and dimmer than “Type Ia” supernovas, leaving behind a “zombie star”. It is thought that this type of supernova is not an explosion but rather a release of energy from the collision of two stars.
Lead author of the study, Takatoshi Ko, a doctoral student in astronomy at the University of Tokyo, said there are currently 20 to 30 candidates for such supernovae, but “SN 1181” is the only example in the Milky Way Galaxy.
The study also found that the high-speed stellar wind, which had been detected in previous studies but whose cause had not been explained, started about 20 years ago and originated from the surface of the “zombie star” in the center.
Ko noted that the computer model showed that “SN 1181” was a “Type Iax” supernova, consistent with data from the European Space Agency (ESA) XMM-Newton Space Telescope and the US Aeronautics and Space Administration (NASA) Chandra X-ray Observatory, and that there were two separate shock regions in the formed nebula.
The “zombie star” at its center may be starting to burn again
Ko emphasized that the first shock zone was caused by a supernova wave caused by the collision of dwarf stars, and noted that the newly emerging shock wave may indicate that the “zombie star” in the center began to burn again in the last 20-30 years, centuries after the initial explosion.
“We assume that ‘SN 1181’ was a Type Iax supernova with an incomplete explosion, which caused the star to reignite. As a result, the material ejected by the explosion could not escape completely and remained under the gravitational influence of the central white dwarf. These materials may have accumulated on the white dwarf due to gravity, causing it to reignite,” Ko said.
A white dwarf was detected spinning at high speed in the center
Albert Zijlstra, an astrophysics professor at the University of Manchester in England, located “SN 1181” in the Milky Way Galaxy in 2021 and determined that the center of the nebula created by the explosion was a rapidly rotating white dwarf the size of Earth that had exhausted its nuclear fuel.
Zijlstra noted that it was unusual for the central zombie star to contain no hydrogen or helium, and that “SN 1181” could be evidence of the merger of two dwarf stars rather than an explosion.
The research was published in the journal “The Astrophysical Journal”.
