It was, at first, a flicker in the data-a faraway active galactic nucleus showing a modest uptick in brightness. Over months, the signal swelled into a cosmic beacon, outshining anything of its kind ever recorded. As astronomers following J2245+3743-a supermassive black hole 500 million times the mass of the Sun-soon came to realise, they were seeing a tidal disruption event on a massive scale: a huge star being torn apart and consumed, producing a flare with the luminosity of 10 trillion suns.
The flare’s rise was dramatic, said astronomer Matthew Graham of Caltech, who is also the ZTF project scientist. First detected on April 2, 2018, by the Zwicky Transient Facility at Caltech’s Palomar Observatory and the Catalina Real-Time Transient Survey, the event brightened by a factor of 40 over a few months. At its peak, it was 30 times more luminous than the previous record-holder, the TDE nicknamed “Scary Barbie.” “This is unlike any AGN we’ve ever seen,” he added. Spectroscopic data from the W. M. Keck Observatory in Hawaii confirmed the extraordinary brightness, ruling out the possibility that the light was simply beamed toward Earth.
The mechanics of a TDE are as violent as they are precise: A star that strays too close to a black hole gets stretched and compressed by tidal forces until it is shredded. The debris forms an accretion stream, spiralling inward, where gravitational energy is converted into intense electromagnetic radiation. In J2245+3743’s case, the doomed star was estimated to be about 30 solar masses, exceptionally large for a TDE. As K. E. Saavik Ford of the City University of New York explained, “Stars this massive are rare, but we think stars within the disk of an AGN can grow larger. The matter from the disk is dumped onto stars, causing them to grow in mass.”
Most of the nearly 100 TDEs so far spotted have occurred in relatively quiet galaxies, where the absence of an active accretion disk makes a TDE’s light easier to spot. In active galactic nuclei, the surrounding disk’s own emissions can mask the flare. But J2245+3743’s enormous scale made its signal impossible to miss. Its accretion disk-which was already feeding the black hole-may have played a part in the star’s growth prior to its destruction, a process consistent with models of stellar evolution in AGN disks.
In other words, the measurement of the luminosity of this flare was a delicate process that involved spectroscopic analysis. The bolometric corrections, using the emission-line spectra taken with instruments like the low-resolution spectrograph on Hale Telescope and Keck’s LRIS, enabled astronomers to confirm that energy was outputted isotropically. Exclusion of relativistic beaming and confirmation that brightness is an intrinsic property of the event were enabled by NASA’s Wide-field Infrared Survey Explorer.
So, the slow fade of the flare revealed another layer of complexity: cosmological time dilation. Since J2245+3743 lies 10 billion light-years away, the expansion of the universe stretches both the wavelength of its light and the passage of time. “Seven years here is two years there. We are watching the event play back at quarter speed,” Graham said. This phenomenon enables astronomers to trace the evolution of the TDE in extraordinary detail, but also means that the actual destruction of the star unfolds much faster in its own frame of reference.
By March 2025, the flare had radiated about 10^54 ergs of energy-the energy equivalent of the Sun’s entire mass converted to radiation via Einstein’s E=mc². Even after two years in its own time, the AGN’s flux remains two magnitudes above its pre-flare level, suggesting that the “stellar snack” is still being digested. Graham likened it to “a fish only halfway down the whale’s gullet.”
This record-breaking flare thus redefines the luminosity upper limits of TDE events and provides new, extended search parameters for incoming events. Long-term, high-cadence surveys, such as ZTF, are necessary to have any hope of discovering events of this rarity, but other examples may be buried in archival data, awaiting detection by new facilities such as the Vera C. Rubin Observatory. The finding serves as a reminder that out there in space-time are countless more such black holes feasting on stars similarly spectacularly, their light awaiting arrival billions of years hence.
