In the heart of distant galaxies, astronomers have witnessed the most violent stellar death throes ever recorded.
A massive star, several times heavier than our Sun, strays too close to the gravitational abyss of a supermassive black hole. It does not explode, not in the conventional sense. Instead, it unravels — shredded by tidal forces, stretched into a stream of stellar debris, and fed to the black hole like spaghetti into a maw. As this cosmic banquet begins, a brilliant flare of light ignites, bright enough to pierce billions of light-years of darkness. It persists not for seconds or hours, but for years.
Move over, supernovae. Astronomers call these phenomena Extreme Nuclear Transients, or ENTs. And they are, quite simply, the most energetic single events the universe has ever shown us since the Big Bang.
“We’ve observed stars getting ripped apart as tidal disruption events for over a decade, but these ENTs are different beasts,” said Jason Hinkle, the University of Hawaiʻi astronomer who led the discovery. “Not only are ENTs far brighter than normal tidal disruption events, but they remain luminous for years, far surpassing the energy output of even the brightest known supernova explosions.”
A New Kind of Massive Cosmic Explosion
The research team first spotted signs of ENTs while combing through public data from the European Space Agency’s Gaia mission. Hinkle noticed two mysterious flares, Gaia16aaw and Gaia18cdj, that didn’t fit any known pattern. Their light curves were smooth and brightened gradually, standing in stark contrast to the erratic flickers of typical black hole outbursts or the sudden flashes of supernovae.
Then came the kicker. A third event, AT2021lwx, was detected independently by the Zwicky Transient Facility. It too shone with a quiet, persistent intensity. “When I saw these smooth, long-lived flares from the centers of distant galaxies,” Hinkle said, “I knew we were looking at something unusual.”
The brightness was just the beginning. These events weren’t just unusual—they were off the cosmic charts. The most luminous of the group, Gaia18cdj, released 2.5 × 10⁵³ ergs of energy — 25 times more than the most powerful known supernovae. For comparison, our Sun will produce just one ten-billionth of that energy over its entire 10-billion-year lifetime.
Not a Supernova, Not an AGN
These were no ordinary explosions. Supernovae couldn’t explain the observations. Neither could the chaotic feeding habits of active galactic nuclei (AGNs), where black holes devour surrounding material. ENTs evolved too smoothly, emitted too much energy, and lasted far too long.
<!– Tag ID: zmescience_300x250_InContent_3
–>
Instead, the team zeroed in on a more exotic possibility: the tidal disruption of a massive star — a stellar body more than three times the mass of our Sun — by an ultramassive black hole, some hundreds of millions of times heavier than the Sun.
As the doomed star strays too close to the black hole, immense gravitational forces tear it apart. The debris forms a temporary disk around the black hole, slowly falling inward and heating up to extreme temperatures. This process releases a sustained blaze of radiation — one that can outshine entire galaxies for months or years.
The Fingerprints of Destruction
To confirm this scenario, Hinkle and his team launched a years-long observational campaign using facilities including the W. M. Keck Observatory and NASA’s Swift satellite. They tracked each ENT across the electromagnetic spectrum, from X-rays to infrared.
The ENTs’ spectra glowed with hot, blue light and broad hydrogen lines, both hallmarks of high-energy accretion onto a black hole. Their blackbody temperatures hovered around 15,000 Kelvin, consistent with models of tidal disruption. And their host galaxies, located at redshifts near 1, placed the events around 7 to 8 billion years in the past — an epoch when star formation and black hole growth were both at their peak.
“ENTs provide a valuable new tool for studying massive black holes in distant galaxies,” said co-author Benjamin Shappee. “Because they’re so bright, we can see them across vast cosmic distances — and in astronomy, looking far away means looking back in time.”
Rarer Than Rare
But, even in a sky filled with telescopes, ENTs are vanishingly rare.
The study estimates their rate at about one per thousand cubic gigaparsecs per year — a volume equivalent to roughly 30 million Milky Way-sized galaxies. That’s 10,000 times rarer than ordinary supernovae.
Their scarcity isn’t surprising. For an ENT to occur, a rare set of cosmic coincidences must align. A massive star must exist in the central region of a galaxy, a supermassive black hole must be present, and the star must drift close enough to be destroyed — but not swallowed whole.
Even then, many ENTs may go unseen. Their dust-shrouded environments may obscure the flare in visible light, and some events may fail to trigger standard detection algorithms. In fact, Gaia itself missed AT2021lwx — likely due to interference from a bright nearby star.
A New Frontier for Black Hole Science
These violent deaths offer more than a fireworks show. They illuminate the invisible. Because ENTs trace interactions between stars and black holes, they open a new window into the mysterious lives of supermassive black holes in distant galaxies — especially those that lie dormant most of the time.
They also push the boundaries of known physics. The sheer energy of ENTs rules out many mechanisms, from radioactive decay in supernovae to spinning magnetars or dense clumps of stellar debris.
“No stellar explosion model can account for what we’re seeing,” the authors write. Instead, ENTs belong to a new — and extreme — frontier of astrophysics.
“These ENTs don’t just mark the dramatic end of a massive star’s life,” Hinkle said. “They illuminate the processes responsible for growing the largest black holes in the universe.”
What’s Next?
Astronomers have just discovered them, but the future of ENT discovery already looks promising. Two next-generation observatories — the Vera C. Rubin Observatory in Chile and NASA’s Roman Space Telescope — are expected to dramatically improve the odds of spotting these rare events. Their wide-field surveys and infrared sensitivity could reveal ENTs from the early universe, as far back as 12 billion years ago.
If so, these cataclysms could become cosmic signposts — blinking beacons that map the rise of supermassive black holes across time and space.
For now, though, the ENTs remain exceptional and few.
The findings appeared in the journal Science Advances.
