Bright star documented in the year 1181 was actually a supernova

Picture Japan in the year 1181, just as the Genpei War (1180-85) was taking root. As political power was being redefined, an unexpected guest star, SN 1181, appeared in the sky.

How do we know? The Azuma Kagami, an ancient diary, recounted not just the details of daily human lives and key events but also these celestial sightings, including the supernova.

Guest star (SN) 1181

Fast forward to the present day, and that once temporary guest star, now known as supernova (SN) 1181, is back in the spotlight.

But not because it shone brightly in the sky, but rather because Takatoshi Ko, a doctoral student from the Department of Astronomy at the University of Tokyo, and his team of researchers have pieced together a mystery that has lasted for centuries.

“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 Saturn’s,” explained Ko.

“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.”

Two dwarf stars created SN 1181

SN 1181 may have faded from view around 840 years ago, but it’s leaving a big impression today. It’s the result of a rare and dramatic event – two white dwarf stars collided, leading to a supernova.

The remnant of this supernova was then left behind as a single, bright, and fast-rotating white dwarf, a cosmic wonder that has piqued the interest of modern astrophysicists.

The SN 1181 remnant presented a perplexing puzzle. Its remnant has two shock regions, but how did they form?

Enter the power of computer modeling and observational analysis. With this tech, the University of Tokyo research team was able to recreate the remnant’s structure and solve this cosmic conundrum.

Tale of stars and supernova

Traditional wisdom led them to believe that when two white dwarfs crash into each other, they should explode and vanish.

But this collision left a white dwarf spinning in space. Was there a stellar wind involved, and if so, when did it start? Their adventurous exploration of space led them to fascinating findings.

According to their calculations, the wind might have started blowing within the last 20-30 years.

“If the wind had started blowing immediately after SNR 1181’s formation, we couldn’t reproduce the observed size of the inner shock region,” said Ko.

“However, by treating the wind’s onset time as variable, we succeeded in explaining all of the observed features of SNR 1181 accurately and unraveling the mysterious properties of this high-speed wind.

The astronomers were also able to simultaneously track the time evolution of each shock region, using numerical calculations.

History meets astronomy

The tale of the SN 1181 is more than just a scientific discovery. It represents a fascinating blend of historical records and modern astronomical techniques. But how does this work?

To begin with, the Azuma Kagami provided invaluable observational data. By analyzing these historical records, astronomers were able to gather crucial information about the appearance and timing of the supernova SN 1181.

In modern times, researchers used this historical data in conjunction with advanced astronomical tools and methods. They could cross-reference the ancient observations with current astronomical data.

As a result, studies successfully pinpointed the exact location of the supernova remnant within the constellation Cassiopeia.

This fusion of history and modern science showcases the importance of preserving and studying historical texts. Through such collaborative efforts, we can gain a more comprehensive understanding of the universe and its history.

On to the next chapter

“The ability to determine the age of supernova remnants or the brightness at the time of their explosion through archaeological perspectives is a rare and invaluable asset to modern astronomy,” said Ko.

“Such interdisciplinary research is both exciting and highlights the immense potential for combining diverse fields to uncover new dimensions of astronomical phenomena.”

This exploration not only furthers our understanding of white dwarf collisions but also sets the stage for unraveling other historical celestial events.

The interdisciplinary nature of this research underscores the importance of preserving ancient records, which serve as invaluable assets in modern scientific inquiries.

But the tale of the guest star (now known as supernova) isn’t over yet.

The team is now gearing up for more observations using the Very Large Array radio telescope and the 8.2 meter-class Subaru Telescope. They’re ready to delve deeper into the mysteries of the universe and hold the cosmos up to a mirror of the past.

Is there more to the tale of SN 1181? Time will tell.

The study is published in the journal The Astrophysical Journal.

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