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Takatoshi Ko

University of Tokyo

Supervisors: Aya Bamba (University of Tokyo) – Toshikazu Shigeyama (Research Center for the Early Universe)

Short Bio: I am a PhD candidate in astronomy at the University of Tokyo, specializing in the origin and diversity of supernova explosions. My research combines observations from world-class telescopes with numerical simulations to explore how white dwarfs explode under different conditions. I have led multi-wavelength studies using radio, optical, and X-ray data, and I often collaborate across disciplines̶from historical astronomy to computational physics.
My current project focuses on unraveling the mystery of SN 1181, a historically recorded supernova whose unusually faint remnant is helping us probe rare pathways of stellar explosions.

Supernova explosions produced by white dwarf binary mergers and their subsequent evolution

Project summary: Over 800 years ago, in the year 1181, astronomers in Japan and China recorded the sudden appearance of a “guest star” in the night sky. It shone brightly for about six months before vanishing from sight. Today, we understand that such events are often supernovae (SNe) the dramatic deaths of stars. For a long time, however, the remnant of this particular explosion remained unknown. Among all historically recorded SNe, SN 1181 stood out as the most recent one for which no remnant had been identified, making it a lingering mystery in both astronomy and history.

The multiband wave observation image of SN 1181 (left) and the schematic picture (right).

What makes SN 1181 especially fascinating is how unusual it is compared to typical supernovae. Most supernovae are incredibly bright and powerful, but this one was exceptionally weak – about a thousand times less energetic than usual. Even more remarkably, while most SNe leave no surviving object at their center, SN 1181 left behind a central object which, for reasons we still don’t fully understand, has recently started showing signs of renewed activity. I use a combination of multi-wavelength observations – from radio to X-ray – as well as detailed computer simulations to reconstruct the evolution of this object and investigate how such a rare and puzzling type of supernova could have occurred.
This research requires crossing traditional boundaries within astrophysics.

On one hand, I work with observational data collected by telescopes around the world; on the other hand, I develop and run theoretical models to simulate how the explosion unfolded and how the remnant evolved over time. This kind of “cross-training” allows me to bridge different perspectives – blending the insights of both observational and theoretical approaches to get a fuller picture. I also collaborate with researchers across disciplines, including plasma physics and historical astronomy, making this a truly interdisciplinary project.

Unexplored filament structure discovered by Fesen et al. 2023. This figure is taken from the fig. 4 of Fesen et al. 2023.

Solving the mystery of SN 1181 is not just about uncovering the story behind an ancient explosion. It also helps expand our understanding of how stars live and die, and the surprising variety of ways they can end their lives. By connecting centuries-old sky records with cutting-edge modern science, this research highlights the enduring and global nature of astronomy – a field that links us with the past, and continues to shape our view of the universe’s future.