Cosmic crime scene reveals ancient supernova aftermath of dead star merger

The ultimate cosmic "cold case" has lingered for 843 years — and now, space detectives may have solved it at last. In 1181 AD, as the Genpei War raged in Japan, a mystery "guest star" briefly flashed over Asia's skies. Astronomers had puzzled over the brief event until 2021, when a team of researchers tracked it to its location in the cosmos. Yet, the cause of the event, now designated supernova (SN) 1181, remained shrouded in mystery.

That was until a team of scientists used computer modeling and observational analysis to recreate the event, finding it was a supernova caused by two "dead star" white dwarfs colliding together. The structure of the remnant white dwarf and leftovers of double shock formation were left behind by the rare occurrence of these two colliding white dwarfs. 

But there is more. The same team found that, as recently as 20 to 30 years ago, high-speed stellar winds began blowing from the surface of the remnant white dwarf. This discovery emphasizes the power of combining the cutting-edge Science of modern Astronomy with historical records to learn about the cosmos. More specifically to these findings, the new results could help better understand the variety of supernovas.

"There are many accounts of this temporary guest star in historical records from Japan, China and Korea. At its peak, the star's brightness was comparable to that of Saturn," team leader Takatoshi Ko, from the Department of Astronomy at the University of Tokyo, said in a statement. "It remained visible to the naked eye for about 180 days until it gradually dimmed out of sight. The remnant of the SN 1181 explosion is now very old, so it is dark and difficult to find."

'Dead stars' clashing in the heavens

White dwarfs are the cooling stellar embers created when stars with masses similar to that of the sun die. As these stars exhaust hydrogen, the fuel needed for nuclear fusion in their cores, the outward push of radiation pressure created by this process also ends. This ends a stellar tug-of-war that the radiation pressure has waged with the inward push of the stars' own gravities for billions of years.

With gravity the victor in this cosmic challenge, these stars' cores undergo gravitational collapse, shedding their outer layers during the so-called red giant phase. Our star, the sun, will undergo this process in around 5 billion years, swelling out to around the orbit of Mars as a red giant and swallowing the inner planets, including Earth. 

Related: Time might be a mirage created by quantum physics, study suggests