It began as a faint flicker in a distant corner of the sky, more than 700 million light-years away. Within days, the light flared, faded, and then, against all expectation, flared again.
What astronomers were seeing was unlike anything in the standard playbook for dying stars. Thanks to an artificial intelligence system that flagged the event in real time, scientists were able to capture every phase of what may be the first recorded case of a massive star exploding as it tried to devour a black hole companion.
The supernova, named SN 2023zkd, was first detected in July 2023 by the Zwicky Transient Facility and analyzed by a team from the Center for Astrophysics | Harvard & Smithsonian (CfA) and the Massachusetts Institute of Technology (MIT). The findings, published in the Astrophysical Journal, reveal the clearest evidence yet that such extreme binary interactions can trigger a stellar detonation.
A Rare Cosmic Catastrophe
The discovery was part of the Young Supernova Experiment, a project designed to catch exploding stars in their earliest stages. The AI system flagged SN 2023zkd within hours of its appearance, giving astronomers a rare chance to follow the explosion in near real time from observatories on the ground and in space.
“Our analysis shows that the blast was sparked by a catastrophic encounter with a black hole companion, and is the strongest evidence to date that such close interactions can actually detonate a star,” said Alexander Gagliano, lead author of the study and fellow at the NSF Institute for Artificial Intelligence and Fundamental Interactions.
The leading explanation is that the massive star and black hole were locked in a decaying orbit. As they drew closer, the black hole’s gravity pulled gas from the star into a surrounding disk. This intense stress may have triggered the explosion before the star could completely engulf the black hole. Another possibility is that the black hole shredded the star entirely, with debris collisions powering the supernova’s light. In either case, the aftermath left a heavier black hole behind.
Unusual Light Patterns
From Earth, SN 2023zkd initially looked like a normal supernova — a single burst of light followed by a gradual fade. But as the months passed, the light curve did something extraordinary: it brightened again. Archival records showed that the system had been slowly brightening for more than four years before the explosion, a rare and telling sign of pre-death instability.
Analysis revealed that the supernova’s light was shaped by layers of gas shed by the star in its final years. The first brightening came from the blast wave colliding with diffuse gas, while the second peak was fueled by a slower collision with a dense, disk-shaped cloud. The structure and timing point to extreme gravitational forces from a nearby compact object.
Key Findings
- Over four years of precursor brightening before explosion.
- Two light-curve peaks, 240 days apart, of similar brightness.
- Evidence of collisions with both fast helium-rich and slower hydrogen-rich gas.
- Estimated 5–6 solar masses of surrounding material powering the peaks.
- Most consistent with a massive helium star merging with a black hole.
The Role of AI and Future Discoveries
“Our machine learning system flagged SN 2023zkd months before its most unusual behavior, which gave us ample time to secure the critical observations needed to unravel this extraordinary explosion,” Gagliano said.
V. Ashley Villar, CfA assistant professor of astronomy and co-author, added: “2023zkd shows some of the clearest signs we have seen of a massive star interacting with a companion in the years before explosion. We think this might be part of a whole class of hidden explosions that AI will help us discover.”
With the Vera C. Rubin Observatory soon scanning the entire sky every few nights, and projects like the Young Supernova Experiment using the Pan-STARRS telescopes to identify new events quickly, astronomers expect to catch more of these rare and complex explosions in action. The goal is to piece together the full life cycle of massive stars in binary systems — from stable orbits to catastrophic endings.
Publication Details
The full study, “Evidence for an Instability-Induced Binary Merger in the Double-Peaked, Helium-Rich Type IIn Supernova 2023zkd,” appears in the Astrophysical Journal. DOI: 10.48550/arXiv.2502.19469
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