The ultimate cosmic “cold case” has remained unsolved for 843 years, but now space detectives may have finally cracked it. In 1181 AD, as the Genpei War raged in Japan, a mysterious “guest star” briefly appeared in the Asian skies. Astronomers were left puzzled by the brief event, until in 2021 a team of researchers tracked its location in space. However, the cause of the event, now dubbed the “cold case,” remains unclear. Supernova (SN) 1181 remained shrouded in mystery.
That was until a team of scientists used computer modeling and observational analysis to recreate the phenomenon and discover that it was a supernova caused by the collision of two “dead stars”, white dwarfs. White dwarf And the rare event of these two white dwarfs colliding left behind traces of a double shock wave formation.
But that’s not all. The same research team was working on high-speed Stellar wind The white dwarf remnant has begun to erupt from its surface. This discovery highlights the power of combining the cutting-edge science of modern astronomy with the historical record to learn about the universe. More specifically to these discoveries, the new results: Various supernovae.
“There are many reports about this Temporary guest appearance “The explosion of SN 1181 has been recorded in historical records in Japan, China and Korea. At its peak, the star’s brightness was comparable to that of Saturn,” team leader Takatoshi Taka of the University of Tokyo’s Department of Astronomy said in a statement. “It remained visible to the naked eye for about 180 days before gradually fading and disappearing from view. The remnants of SN 1181’s explosion are now so old that they are dim and difficult to find.”
Related: Peering into the remnants of an 800-year-old supernova, researchers observe a “zombie” star
“Dead Stars” Colliding in the Sky
White dwarfs are the cooling embers of stars similar in mass to our Sun that are created when they die. When these stars run out of energy, Hydrogen, the fuel necessary for nuclear fusion At the star’s core, the outward push of radiation pressure created by this process also ends, ending a billion-year-old stellar tug-of-war between radiation pressure and the inward push of the star’s own gravity.
When gravity wins this cosmic challenge, the cores of these stars undergo gravitational collapse, shedding their outer layers during what’s called a “collapse.” Red giant phase Our star, The sun will go through this process in about 5 billion years. It swells up to around the eye socket, Mars It has become a red giant and is engulfing the inner planets. Earth.
Eventually, the outer layers of these dead stars drift away, leaving the cooling stellar cores as cosmic embers around the universe. Size of the Earth It is called a white dwarf.
Diagram showing the evolution of the supernova remnant SNR 1181 (Image provided by: T.Ko)
The Sun exists alone, but about 50% of stars of a similar mass Binary System They can also merge with other stars, which themselves become dense, compact white dwarfs.
As White dwarf binary As the white dwarfs spin around each other, they send out tiny ripples in space and time called “gravitational waves,” carrying away angular momentum and pulling the white dwarfs together. Conventional wisdom holds that the collision would destroy both white dwarfs, but in rare cases, a phenomenon called “gravitational waves” does occur. Iax type supernova What’s left behind is a single, rapidly rotating white dwarf star.
This new study suggests that SNR 1181 is just such a supernova remnant. Observations of the remnant have revealed that SNR 1181 apparently consists of an outer and an inner impact region. Ko and his colleagues analyzed X-ray data from SNR 1181 to create a computer model to explain the observations and reconstruct the evolution of the structure in this phenomenon. For example, they hoped to understand why the colliding dead star left behind a daughter white dwarf.
Diagram showing the two shock wave regions of the remnant SNR 1181. The bright white area in the center is the white dwarf star. (Image credit: T. Ko, H. Suzuki, K. Kashiyama et al./The Astrophysical Journal (2024))
Shortly after the white dwarf formed, the object wasStellar wind But the team discovered something that defied expectations.
“If the wind had started blowing immediately after SNR 1181’s formation, we would not have been able to reproduce the observed size of the internal shock wave regions,” explains Ko. “However, by treating the time when the wind started blowing as a variable, we were able to accurately explain all of SNR 1181’s observed features and unravel the mysterious nature of this high-speed wind. Using numerical calculations, we were also able to simultaneously track the evolution of each shock wave region over time.”
Even more surprising to the team was their discovery that the stellar wind from this collision-generated white dwarf likely began very recently, perhaps around 20 years ago.
This finding could suggest that some nuclear fusion is still occurring within the white dwarf, causing it to “start burning” again. This could be the result of a type Iax supernova that would have been seen by combatants on Earth fighting for control of Japan during the Genpei War, a conflict between the Taira and Minamoto clans that began in 1180 and ended five years later. The battle saw the downfall of the Taira and the establishment of the Kamakura Shogunate.
The team behind these discoveries aim to confirm their results with further observations of SNR 1181. Very large arrays The New Mexico (VLA) radio telescope and the 8.2-meter Subaru Telescope At the summit of Mauna Kea in Hawaii.
“The ability to determine the age and brightness of supernova remnants from an archaeological perspective is a rare and valuable asset to modern astronomy,” said Coe. “Interdisciplinary research like this is exciting and highlights the great potential for combining different fields to discover new aspects of astronomical phenomena.”
The study was published July 5. Astrophysical Journal.
