Supernova SN 1181 was seen with the naked eye in Japan and Chine 843 years ago in 1181 CE. However, its remanent could not be identified for a long time. In 2021, the nebula Pa 30 situated towards the constellation Cassiopeia was identified with the supernova SN 1181. The white dwarf star at the centre of the Pa 30 nebula, now called Parker’s star, is the remanent of supernova event which was result of merger of two white dwarfs. This supernova event was rare and is classified as SN Type Iax. A recent study indicates that the remanent of this supernova is undergoing fusion again which began recently around 1990.
Earth and Sun will not remain the way they are for ever. Earth will remain habitable for another 4 billion years till Sun enters its end stage (barring manmade or natural disasters like nuclear war, impact with an asteroid, massive volcanic eruption, etc).
Sun is an ordinary, relatively young star in our home galaxy. Like all stars, Sun also has a life course –it was born about 4.6 billion years ago and will die in future. In about 4 billion years from now, it will run out of hydrogen that fuels nuclear fusion in its core for energy generation when gravitational collapse begins. Increased pressure due to core collapse will trigger nuclear fusion of heavier elements in the core. As a result, temperature of Sun will increase, and the outer layer of solar atmosphere will expand far out in the space and engulf nearby planets including Earth. This red giant stage will continue for about a billion year. Eventually, Sun will collapse to become a white dwarf.
Unlike the way in which Sun will die in future, the end stage of a massive of star is an astronomical event. When stars heavier than 8 solar masses run out of fuel for nuclear fusion and are unable to produce adequate energy to counteract strong inward gravitational pull, their core collapse in a short period of time. The implosion creates enormous shock waves and powerful luminous transient event called supernova and a compact remanent result (the supernova remanent will be a neutron star if the mass of the original star is between 8 to 20 solar masses. If the mass of the original star is more than 20 solar masses, then the supernova remanent will be a black hole).
Supernovae may also be triggered by the sudden re-ignition of nuclear fusion in a white dwarf when its temperature is raised enough to trigger runaway nuclear fusion. This happens due to merger with another white dwarf or due to an accumulation of material from a binary companion.
Supernova SN 1181
In the last two millennia, nine luminous transient astronomical events (supernova) have been observed in our home galaxy Milky Way. One such powerful event was observed and chronicled in Japan and China about 843 years ago in 1181 CE. The “Guest Star” was visible for 185 days from 6 August 1181 to 6 February 1182. This was named Supernova 1181 (SN1181) however, identification of its remanent could not be confirmed until recently.
Identification of Supernova Remanent SNR 1181
A circular infrared emission nebula was found in NASA’s data archive in 2013 by an amateur astronomer Dana Patchick who named it nebula Pa 30. Professional astronomers observed a faint patch of diffuse emission but did not find hydrogen emission. A massive dwarf (WD) star was discovered inside the infrared shell few years later in 2019 which showed unique properties and was thought to have formed because of merger of Carbon-Oxygen white dwarf (CO WD) and Oxygen-Neon white dwarf (ONe WD). The merger of the two white dwarfs caused a supernova event. Subsequently, in 2021, it was found that the nebula Pa 30 exhibited sulphur emission lines and an expansion velocity of 1100 km/sec. Its age was estimated to be around 1000 years and was found to be located around the point where the ‘guest star’ was seen in 1181 CE. These findings led to identification of Pa 30 nebula situated towards the constellation Cassiopeia with supernova seen over eight centuries ago. The white dwarf star at the centre of the Pa 30 nebula, now called Parker’s star is the remanent of supernova event SN1181 and the event is classified as SN Type Iax. Evidence from a later study published in 2023 support the above findings.
The high-speed stellar wind started blowing recently after the year 1990
The remnant of SNR 1181was created by the merger of two white dwarfs. Usually, when two white dwarfs merge, they explode and disappear. However, this merger created a rare type of supernova called a Type Iax and left behind a single, fast-spinning white dwarf. The spinning white dwarfs release fast-flowing streams of particles (called stellar wind) immediately after its formation. In this case, the central star of the P 30 nebula shows many filaments converging near the central star due to fast stellar wind blowing over the shell of supernova ejecta. Astronomers observed an outer shock region and an inner shock region in SNR 1181.
In a recent study, researchers analysed the latest X-ray data and developed a model that showed that the observed size of the inner shock region is not commensurate with the expected size had the stellar wind begun blowing soon after the formation of the remanent. As per their computer model, the actual observed size of the inner shock region indicates that the high-speed stellar wind started blowing recently after the year 1990. This is quite astounding. This may have happened because some supernova ejecta fell back to the white dwarf surface later which increased the temperature and pressure beyond the threshold to allow onset of thermonuclear reaction and burning restarted. The researchers are now working towards validation of the model.
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References:
- Ritter A., et al 2021. The Remnant and Origin of the Historical Supernova 1181 AD. The Astrophysical Journal Letters. 918 (2): L33. arXiv:2105.12384. DOI: https://doi.org/10.3847/2041-8213/ac2253
- Schaefer B.E., 2023. The path from the Chinese and Japanese observations of supernova 1181 AD, to a Type Iax supernova, to the merger of CO and ONe white dwarfs. Monthly Notices of the Royal Astronomical Society, Volume 523, Issue 3, August 2023, Pages 3885–3904. DOI: https://doi.org/10.1093/mnras/stad717 . Preprint version arXiv:2301.04807
- Takatoshi Ko, et al 2024. “A dynamical model for IRAS 00500+6713: the remnant of a type Iax supernova SN 1181 hosting a double degenerate merger product WD J005311,” The Astrophysical Journal: July 5, 2024, DOI: https://doi.org/10.3847/1538-4357/ad4d99
- University of Tokyo. Press release – Fresh wind blows from historical supernova. Posted 5 July 2024. Available at https://www.u-tokyo.ac.jp/focus/en/press/z0508_00361.html
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