Biggest Boom Since the Big Bang: Hawaiʻi-Based Astronomers Uncover the Most Energetic Explosions In The Universe Yet Discovered

Releasing more energy than 100 supernovae, Extreme Nuclear Transients (ENTs) are the most energetic transients yet observed

Credit: W. M. Keck Observatory / Adam Makarenko
Maunakea, Hawaiʻi – Astronomers using data from the W. M. Keck Observatory on Maunakea, Hawaiʻi Island discovered the most energetic cosmic explosions discovered to date, naming the new class of events “extreme nuclear transients” (ENTs). These extraordinary phenomena occur when massive stars—at least three times heavier than our Sun—are torn apart after wandering too close to a supermassive black hole. Their disruption releases vast amounts of energy visible across enormous distances.

The team’s findings were detailed today in the journal Science Advances.

“We’ve observed stars getting ripped apart as tidal disruption events for over a decade, but these ENTs are different beasts, reaching brightnesses nearly ten times more than what we typically see,” said Jason Hinkle, who led the study as the final piece of his doctoral research at the University of Hawaiʻi’s Institute for Astronomy (IfA). “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.”

The immense total energy output of these ENTs are truly unprecedented. The most energetic ENT studied, named Gaia18cdj, emitted an astonishing 25 times more energy than the most energetic supernovae known. While typical supernovae emit as much energy as the Sun does in its 10 billion-year lifetime, ENTs radiate the energy of 100 Suns.

Caption: Artist’s concept of the formation of Extreme Nuclear Transients (ENTs). Credit: W. M. Keck Observatory / Adam Makarenko.
ENTs were first uncovered when Hinkle began a systematic search of public surveys for long-lived flares emanating from the centers of galaxies. He identified two unusual flares in data from the European Space Agency’s Gaia mission that were detected in 2016 and 2018.

“Gaia doesn’t tell you the physics of the event, just that something changed in brightness,” said Hinkle. The discovery launched a multi-year follow-up campaign to figure out what these sources were.

Meanwhile, a third event with similar properties was discovered in 2020 by the Zwicky Transient Facility (ZTF) and reported independently by two teams in 2023. Using data from the Keck Observatory Archive (KOA) for this new ZTF object showed it was similar to the two Gaia ENTs, adding strong support that ENTs are a distinct new class of extreme astrophysical events.

Drawing on observations from a wide array of ground- and space-based telescopes, the team determined these extraordinary events could not be supernovae because they release far more energy than any known stellar explosion. The sheer energy budget, combined with their smooth and prolonged light curves, firmly pointed to an alternative mechanism: accretion onto a supermassive black hole.

However, ENTs differ significantly from normal black hole accretion, when materials surrounding the black hole heat up and emit light and typically show irregular and unpredictable changes in brightness. The smooth and long-lived flares of ENTs indicate a distinct physical process—the gradual accretion of a disrupted star by a supermassive black hole.

Benjamin Shappee, Associate Professor at IfA and study co-author, emphasized the implications: “ENTs provide a valuable new tool for studying massive black holes in distant galaxies. Because they’re so bright, we can see them across vast cosmic distances—and in astronomy, looking far away means looking back in time. By observing these prolonged flares, we gain insights into black hole growth during a key era known as cosmic noon, when the universe was half its current age when galaxies were happening places—forming stars and feeding their supermassive black holes 10 times more vigorously than they do today.”

The rarity of ENTs, occurring at least 10 million times less frequently than supernovae, makes their detection challenging and dependent on sustained monitoring of the cosmos. Future observatories like the Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope promise to uncover many more of these spectacular events, revolutionizing our understanding of black hole activity in the distant, early universe.

“These ENTs don’t just mark the dramatic end of a massive star’s life,” stated Hinkle. “They illuminate the processes responsible for growing the largest black holes in the universe.”

Artist animation of Extreme Nuclear Transients (ENTs). The sheer energy budget, combined with their smooth and prolonged light curves, indicate an alternative mechanism: accretion onto a supermassive black hole. ENTs differ significantly from normal black hole accretion, when materials surrounding the black hole heat up and emit light and typically show irregular and unpredictable changes in brightness. The smooth and long-lived flares of ENTs indicate a distinct physical process—the gradual accretion of a disrupted star by a supermassive black hole. Credit: W. M. Keck Observatory / Adam Makarenko.
Paper: https://www.science.org/doi/10.1126/sciadv.adt0074

Media Contact: Meagan O’Shea – moshea@keck.hawaii.edu

ABOUT KOA
The Keck Observatory Archive (KOA) is a collaboration between the NASA Exoplanet Science Institute (NExScI) and the W. M. Keck Observatory (WMKO). NExScI is sponsored by NASA’s Exoplanet Exploration Program, and operated by the California Institute of Technology in coordination with the Jet Propulsion Laboratory (JPL).

ABOUT W. M. KECK OBSERVATORY
The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaiʻi feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. For more information, visit: www.keckobservatory.org