An international research team led by Chinese scientists has discovered new evidence about Type II-P supernovae, suggesting that some of these stellar explosions may originate from merged binary stars.

The study, involving researchers from China, Greece, the United Kingdom, the United States, Ireland, and Switzerland, was recently published in the journal Science Bulletin.

Type II-P supernovae account for about 40 percent of all observed supernovae. Understanding the progenitor stars, or the stars that explode as these supernovae, is essential for studying massive star evolution, stellar explosion mechanisms, and the formation of compact objects.

Though theorists suggested these supernovae might originate from binary systems, direct evidence was elusive because progenitors from both single and binary systems appear as red supergiants before exploding.

Using Hubble Space Telescope data, the research team identified the red supergiant progenitor of supernova SN 2018gj. Although it had typical properties, it was located in an old stellar environment at the edge of its host galaxy, and the supernova's light curve had a short "plateau" phase.

The team used methods including direct progenitor detection, environmental analysis, and hydrodynamic simulations to demonstrate the supernova's binary origin.

"This work is a prime example of deep collaboration between observational and theoretical astronomers. It offers a new strategy to uncover the hidden origins of supernovae," said Sun Ningchen, co-first author and an associate professor at the University of Chinese Academy of Sciences and the National Astronomical Observatories of the Chinese Academy of Sciences.

"By utilizing state-of-the-art binary evolution simulations, we also uncovered the complex evolutionary history of the progenitor system, which involved mass transfer and the eventual merger of two stars," said Emmanouil Zapartas, co-first author of the study and a research fellow at the Institute of Astrophysics at the Foundation for Research and Technology-Hellas and National and Kapodistrian University of Athens in Greece.

"One of the major achievements of this study was the careful examination of all of these possibilities, utilizing among other things some of the major space telescopes, such as the Hubble Space Telescope and the Spitzer Space Telescope, to obtain a comprehensive story for this supernova and the history of its progenitor. We have now finally identified a long predicted, but so far elusive merger progenitor for this type of supernova," said Philipp Podsiadlowski, a co-author and leading theoretical astrophysicist at the London Centre for Stellar Astrophysics and the University of Oxford in the UK.

Niu Zexi, co-first author and special research assistant at UCAS, added: "It also highlights the crucial role of binary interactions in shaping the observational diversity of Type II-P supernovae."

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