It had all begun as a small, forgotten point of light buried deep in the extensive archives of a 2018 sky survey-the quiescent entry of an event that was to reveal itself as the most luminous black hole flare ever recorded. The cosmic eruption was emanating from an active galactic nucleus bearing the designation J2245+3743 and blazed with the combined brilliance of 10 trillion suns, erupting 10 billion light-years away when the universe was young.
The great flare was created through a tidal disruption event in which gravity of the supermassive black hole rips apart a star that comes too close. In this case, a star at least 30 times more massive than the Sun fell into the gravitational maw of a 500-million-solar-mass black hole. Stellar material spiralled inward, and, under enormous gravitational forces, matter was converted into radiant energy, creating a flare 30 times more luminous than any previously observed black hole flare.
It was first detected by the Zwicky Transient Facility at the Palomar Observatory of Caltech, part of a network of ground-based telescopes surveying the sky for transient events. In 2018, it brightened by a factor of 40 in several months to reach peak luminosity and then started to fade away. Follow-up spectroscopy at the time yielded little, and the event was set aside. It wasn’t until 2023 that astronomers looked again at the data, calculating the immense distance involved and, consequently, the tremendous energy output implied by such brightness shining across billions of light-years.
“This is really a one-in-a-million object,” said Matthew Graham, Caltech research professor of astronomy and lead author of the study. “The energetics show this object is very far away and very bright. This is unlike any AGN we’ve ever seen.” The team ruled out alternative explanations such as relativistic jets aimed directly at Earth or a massive supernova. Observations from NASA’s retired Wide-field Infrared Survey Explorer confirmed the flare’s emission was isotropic that is radiating in all directions.
Cosmological time dilation partly explains the longevity of the flare: Seven years here is two years there. We are watching the event play back at quarter speed. The expansion of space stretches not only light wavelengths but also time intervals, so this effect means that ground-based telescopes can monitor the flare’s evolution over a period of years. The event can still be seen today, its light slowly fading as the black hole continues to devour the remains of the star “a fish only halfway down the whale’s gullet,” as Graham put it in a colorful figure of speech.
Events as large as this one are extremely rare, especially in active galactic nuclei. In many cases, the presence of an AGN could mask most TDEs, making their detection much more challenging. Nevertheless, the enormous scale of J2245+3743’s flare punctured through the background variability. Previous record-holders, such as the event nicknamed “Scary Barbie,” included far smaller stars and produced flares roughly 30 times weaker. The finding emphasizes that stars embedded within the disks of AGNs can grow to exceptional masses-continuously fed by the dense material surrounding the supermassive black hole-prior to their eventual cataclysmic demise.
The flare represents a unique laboratory for the study of extreme accretion physics from an astrophysical point of view. The energy release is rivaling the total conversion of the Sun’s mass into energy via the Einstein relation E = mc²-sustained over several years. Events like this serve to emphasize the complex interaction that exists between a black hole and its surroundings, probing into conditions in the early universe and modeling variability in AGN. “to probe the interaction of supermassive black holes with their environments early in the universe.” said Joseph Michail, of the Harvard-Smithsonian Center for Astrophysics.
The group is continuing to mine ZTF archives for comparable events and looks forward to future detections from the Vera C. Rubin Observatory, whose wide-field surveys may uncover other unusually massive tidal disruptions. Every such event opens up a new frontier in high-energy astrophysics, revealing the dynamic and violent processes shaping galaxies across cosmic time.
