Black hole blast outshines 10 trillion Suns

That scenario best explains the findings of a new Nature Astronomy study describing the most powerful and most distant flare of energy ever seen from a supermassive black hole. The object was first detected in 2018 by the Zwicky Transient Facility (ZTF), a sky survey funded by the US National Science Foundation (NSF) and operated at Caltech's Palomar Observatory. It was also tracked by the Catalina Real-Time Transient Survey, another NSF-funded Caltech project. The flare brightened dramatically -- by a factor of 40 within months -- and at its peak was 30 times more luminous than any black hole flare observed before. At maximum intensity, it shone with the light of 10 trillion suns.

A Glimpse into the Early Universe

The black hole responsible is an active galactic nucleus (AGN), a type of black hole that actively feeds on surrounding matter. Known as J2245+3743, this AGN is estimated to have a mass 500 million times greater than the Sun and lies roughly 10 billion light-years from Earth. Because light takes time to travel across such vast distances, astronomers are seeing this event as it occurred when the universe was still young.

"The energetics show this object is very far away and very bright," says study lead author Matthew Graham, research professor of astronomy at Caltech and project scientist for ZTF. "This is unlike any AGN we've ever seen."

Although the flare is gradually fading, astronomers continue to observe it. Time itself passes differently at such distances -- a phenomenon known as cosmological time dilation. As Graham explains, "As the light travels across expanding space to reach us, its wavelength stretches as does time itself." Because of this, long-term sky surveys such as ZTF and Catalina are crucial. "Seven years here is two years there. We are watching the event play back at quarter speed," he adds.

The Star That Was Torn Apart

To uncover what could have caused this extraordinary outburst, the researchers tested various possibilities and determined the most likely cause to be a tidal disruption event (TDE). A TDE happens when a star ventures too close to a supermassive black hole and is torn apart by its immense gravity. The star's material is gradually drawn in and consumed. Since the flare from J2245+3743 is still visible, astronomers believe the black hole is in mid-meal, "like a fish only halfway down the whale's gullet," Graham says.

If this explanation is correct, the doomed star was at least 30 times as massive as the Sun. The previous record-holder for the largest known TDE -- an event nicknamed Scary Barbie -- was about 30 times weaker and involved a star only three to ten times the Sun's mass.

A Rare Event Inside a Feeding Black Hole Disk

Most of the roughly 100 known TDEs have not occurred within AGN systems, which are already surrounded by dense, swirling disks of material feeding the central black hole. These bright environments usually hide other events, making TDEs difficult to detect. However, the sheer brightness of J2245+3743 made it stand out clearly.

Initially, astronomers saw nothing unusual. When the object was first identified in 2018, spectra obtained with the 200-inch Hale Telescope at Palomar Observatory showed no special features. But by 2023, the flare was fading more slowly than expected. A follow-up spectrum from the W. M. Keck Observatory in Hawai'i revealed the AGN's extreme luminosity.

Confirming the Brightest Flare Ever Recorded

"At first, it was important to establish that this extreme object was truly this bright," says co-author K. E. Saavik Ford of the City University of New York (CUNY) Graduate Center, Borough of Manhattan Community College, and the American Museum of Natural History (AMNH). Ford explains that one alternative was that the flare's light was being beamed directly toward Earth, but data from NASA's former Wide-field Infrared Survey Explorer (WISE) mission ruled that out. With other possibilities eliminated, the team concluded that J2245+3743 represents the brightest black hole flare ever observed.

"If you convert our entire Sun to energy, using Albert Einstein's famous formula E = mc2, that's how much energy has been pouring out from this flare since we began observing it," Ford notes.

A Star's Destruction Unmatched by Supernovae

After verifying the flare's record-breaking intensity, the researchers explored its origin. "Supernovae are not bright enough to account for this," Ford says. The most consistent explanation is a supermassive black hole slowly tearing apart a colossal star.

"Stars this massive are rare," Ford continues, "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."

Searching for More Cosmic Giants

Discovering a black hole devouring such a massive star suggests that similar events might be happening elsewhere in the universe. The research team plans to search through more ZTF data to locate other examples, and future observatories such as the NSF and Department of Energy's Vera C. Rubin Observatory may also uncover additional large TDEs.

"We never would have found this rare event in the first place if it weren't for ZTF," Graham says. "We've been observing the sky with ZTF for seven years now, so when we see anything flare or change, we can see what it has done in the past and how it will evolve."

The Team Behind the Discovery

The study, titled "An Extremely Luminous Flare Recorded from a Supermassive Black Hole," was supported by the NSF, the Simons Foundation, NASA, and the German Research Foundation. Co-authors include Caltech researchers Andrew Drake, Yuanze Ding (MS '25), Mansi Kasliwal (PhD '11), Sam Rose, Jean Somalwar (now a postdoc at UC Berkeley), George Djorgovski, Shri Kulkarni, and Ashish Mahabal; Tracy Chen and Steven Groom of Caltech's IPAC astronomy center; and Daniel Stern of NASA's Jet Propulsion Laboratory (managed by Caltech). Additional contributors include Barry McKernan (CUNY Graduate Center, Borough of Manhattan Community College, and AMNH); Matteo Cantiello (Flatiron Institute and Princeton University); Mike Koss (Eureka Scientific); Raffaella Margutti (UC Berkeley); Phil Wiseman (University of Southampton, UK); Patrik Veres (Ruhr University, Germany); and Eric Bellm (University of Washington).

Caltech's ZTF is funded by the NSF and international partners, with additional support from the Heising-Simons Foundation and Caltech. Data are processed and archived by Caltech's IPAC, and NASA funds ZTF's search for near-Earth objects through its Near-Earth Object Observations program.