That picture has now changed with real time observations of the supernova SN 2022esa, which captured the collapse of a massive star leading to a supernova and the formation of a black hole. A team at Kyoto University set out to test whether all very massive stars, those at least 30 times the mass of the Sun, die without visible fireworks or whether some end their lives in especially energetic and luminous explosions.

Their work led to the discovery of a type Ic supernova interacting with dense circumstellar material, classified as a type Ic-CSM event, which appears to mark the explosion of a Wolf-Rayet star. Wolf-Rayet stars are extremely massive and luminous, and many astronomers regard them as prime progenitors for the formation of black holes.

To probe the nature of this unusual supernova, the team combined observations from the Seimei telescope in Okayama with those from the Subaru telescope in Hawaii. Using these facilities, they tracked the evolution of SN 2022esa and were able to confirm its identity as an Ic-CSM supernova, showing that the birth of at least some black holes is not silent but instead accompanied by strong electromagnetic signals.

At late times, about a year after discovery, images from Subaru showed SN 2022esa in its host galaxy 2MFGC 13525 after it had faded in brightness by more than a factor of 100 compared with its initial peak. The researchers noted that the spectral features that define Ic-CSM supernovae typically emerge only in such late phases, and that extracting them requires dedicated follow up using 8 meter class telescopes like Subaru.

The supernova also revealed a striking pattern in its light curve, displaying a clear and stable period of roughly one month in the evolution of its brightness. From this behavior the team inferred that the progenitor system underwent stable periodic eruptions about once a year in the years before the star finally exploded.

Such regular activity points strongly to a binary origin, because stable periodicity of this kind is difficult to explain with a single star. The researchers concluded that the progenitor was most likely a Wolf-Rayet star in a close binary with another massive star, or possibly already orbiting a black hole companion.

The eventual fate of such a system, once both massive components complete their evolution and collapse, is expected to be a pair of black holes in orbit around each other. Systems of this kind are key sources for gravitational wave detectors, which can observe the ripples in spacetime produced when black hole binaries spiral together and merge.

"The fates of massive stars, the birth of a black hole, or even a black hole binary, are very important questions in astronomy," says first author Keiichi Maeda. "Our study provides a new direction to understand the whole evolutional history of massive stars toward the formation of black hole binaries."

The work also highlights the advantages of coordinating different types of telescopes with complementary capabilities. Seimei provided flexible and rapid response observations, while Subaru contributed the high sensitivity needed for deep, late phase spectroscopy and imaging of the fading supernova.

The team plans to keep using both facilities for future campaigns targeting astronomical transients and stellar explosions such as supernovae. "We expect many interesting discoveries on the nature of astronomical transients and explosions like supernova," Maeda adds.

The research is reported in the paper "Peculiar SN Ic 2022esa: An explosion of a massive Wolf-Rayet star in a binary as a precursor to a BH-BH binary?" published on 30 December 2025 in Publications of the Astronomical Society of Japan. The article is available with the doi 10.1093/pasj/psaf140.

Research Report:Peculiar SN Ic 2022esa: An explosion of a massive Wolf-Rayet star in a binary as a precursor to a BH-BH binary?

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