Biggest and brightest black hole flare ever seen reveals a cosmic feeding frenzy

While some black holes graze lightly, others devour their meals. In 2018, sky surveys picked up an outburst that brightened by a factor of 40 within a few months and, at its peak, shone with the light of about ten trillion suns.

The flare now stands as the most powerful and most distant black hole flare ever recorded.

The culprit sits ten billion light-years away in a galaxy whose core hosts an active galactic nucleus (AGN) called J2245+3743. Its central black hole is a heavyweight, roughly 500 million times the mass of our Sun.

“The energetics show this object is very far away and very bright,” said lead author Matthew Graham, a research professor of astronomy at Caltech. “This is unlike any AGN we’ve ever seen.”

Black hole flare J2245+3743

Because the universe expands, distant events don’t just look far away. They play back in slow motion. As light travels to us across stretching space, its wavelength lengthens and time appears to dilate. For J2245+3743, that matters.

Long-lived surveys like ZTF and the Catalina Real-Time Transient Survey can follow the full arc of an event that, locally, is unfolding faster.

“Seven years here is two years there. We are watching the event play back at quarter speed,” said Graham.

The flare from the distant black hole has been fading but is still going – long enough to let astronomers test and discard several competing explanations.

J2245+3743 breaks records

Active galactic nuclei are already luminous. They shine as gas in a giant, rotating disk that falls toward the black hole and heats up.

AGN can also flare as their feeding ebbs and surges. That background variability can mask rarer, brighter episodes.

In 2018, the first spectrum of J2245+3743 taken with the 200-inch Hale Telescope at Palomar looked ordinary.

Only later, in 2023 – when the decay curve lagged expectations – did a fresh spectrum from the W. M. Keck Observatory in Hawai‘i reveal just how extreme the event was.

The team checked whether the source might be beaming light toward us, an effect that could mimic extreme brightness.

“At first, it was important to establish that this extreme object was truly this bright,” said co-author K. E. Saavik Ford, a professor at CUNY.

Data from NASA’s former WISE mission helped rule out a jet aimed at Earth. With more mundane options – like a particularly luminous supernova – also failing to fit, one scenario rose to the top.

Star shredded by black hole

The favored picture is a tidal disruption event, or TDE – a close-pass star torn apart by a black hole’s gravity. Shredded stellar debris spirals in and feeds the black hole for months to years, lighting up the galactic core.

Most known TDEs occur around black holes that are not already active, so their flares stand out more cleanly.

J2245+3743 is different – it’s a feeding supermassive black hole, and the TDE flare towered over the disk’s usual burble, making it visible even against that bright backdrop.

The feast isn’t finished

How big was the doomed star? Modeling suggests at least 30 solar masses – an absolute giant. That scale already dwarfs the previous record holder, the ZTF event nicknamed “Scary Barbie” (ZTF20abrbeie).

ZTF involved a star between three and ten solar masses and produced a flare roughly 30 times weaker than J2245+3743.

The ongoing glow from J2245+3743 implies the feast isn’t finished. In Graham’s vivid phrasing, the star is like “a fish only halfway down the whale’s gullet.”

“If you converted 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,” said Ford.

Where monster stars are born

Stars this massive are rare in ordinary galaxies. But the disk of an AGN is no ordinary nursery.

It’s a dense, turbulent reservoir of gas orbiting close to a black hole. In that environment, “the matter from the disk is dumped onto stars, causing them to grow in mass,” Ford noted.

If a star grows large enough within the disk and then strays too near the black hole, the stage is set for an outsized TDE – the kind of event that could explain the unmatched brightness of J2245+3743.

This idea also helps square the timing. TDEs in AGN are tricky to spot because “normal” feeding flares can hide them.

Here, the stellar snack was so massive that the black hole’s feast overwhelmed the background, letting telescopes see the flare’s rise and protracted fall.

What this flare reveals next

The discovery hinged on persistence. ZTF, based at Caltech’s Palomar Observatory, scans the sky nightly for changing objects. Catalina does the same.

That cadence meant the team could catch the initial surge, compare it to years of prior behavior, and keep watching as the light curve evolved.

“We never would have found this rare event in the first place if it weren’t for ZTF,” said Graham.

“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.”

Lessons from J2245+3743

The result is more than a single splashy record. It’s a signpost. If a 500-million-solar-mass black hole can shred a 30-solar-mass star inside its own disk then similar events are likely playing out elsewhere.

Mining ZTF’s archive may turn up more of them. And within a few years, the NSF and Department of Energy’s Vera C. Rubin Observatory will bring an even deeper, wider view of the changing sky.

Unusually large TDEs like J2245+3743 could become a class, not an exception.

This black hole ended a star’s tale before it could write its last chapter – no supernova, no black hole of its own. The irony is sharp: a star destined to explode was instead swallowed whole by a larger cosmic object.

In the process, it gave astronomers a backlit view of how extreme black holes feed, how time stretches across cosmic distances, and how the universe’s brightest fireworks can still surprise us.

The research is published in the journal Nature Astronomy.

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