Despite its seemingly calm facade, the universe is a stage for immense cosmic violence. It’s filled with catastrophic events like colliding galaxies, the explosive demise of colossal stars (supernovae), potent X-ray bursts, and black holes that voraciously consume stars.
Amidst this cacophony of cosmic phenomena, astronomers have long held gamma-ray bursts (GRBs)—spectacular explosions born from the formation of black holes—as the universe’s most intense outbursts. These incredibly energetic events travel across immense cosmic distances, making them the brightest electromagnetic displays witnessed since the Big Bang, the widely accepted theory for the universe’s creation and development.
However, a groundbreaking discovery by astronomers at the University of Hawaii’s Institute for Astronomy (IfA) has unveiled an entirely new class of cosmic events, far surpassing the power of even GRBs. They’ve named these ‘extreme nuclear transients’ (ENTs). In astronomical terms, a ‘transient’ is any celestial object that dramatically alters its brightness over a relatively short span of time.
Mysteries of the Cosmos
These remarkable findings, recently published in the scientific journal Science Advances, detail incredible events where colossal stars strayed too near to the monstrous black holes residing at the hearts of galaxies and were, quite literally, devoured. Their demise mirrors the Greek myth of Icarus, who, flying too close to the sun, met his end when his waxen wings melted.
As explained by Jason Hinkle, the lead author of the IfA study, ENTs are fueled by material accreting from the remnants of massive stars, at least three times the mass of our Sun, which have been violently shredded by a supermassive black hole.
Black holes stand as some of nature’s most enigmatic creations, with the supermassive black holes nestled at galactic cores being the largest. Our own Milky Way galaxy hosts one such giant, known as Sagittarius A*.
When a star approaches a black hole’s event horizon—the boundary beyond which nothing, not even light, can escape—it is subjected to incredible tidal forces. These forces stretch and compress the star into a long, thin, spaghetti-like stream, unleashing immense quantities of electromagnetic energy. This spectacular release is precisely what astronomers categorize as an ENT.
These dazzling cosmic ribbons travel across vast stretches of space, emitting radio waves that remain detectable for years, providing a unique opportunity for astronomers to study them. Indeed, ENTs are so potent that scientists now consider them to be the most colossal explosions to have occurred since the very dawn of the universe with the Big Bang.
Dr. Hinkle emphasized that ENTs represent the most energetic class of transient events ever identified, releasing up to ten times more energy than anything previously observed.
Cosmic Shredding
Dr. Hinkle’s discovery of ENTs came serendipitously as he sifted through vast datasets from the European Space Agency’s Gaia spacecraft, which spent over a decade meticulously mapping our Milky Way galaxy.
He explained that their search focused on identifying ‘smooth, high-amplitude, and long-lived events.’ Starting in 2020, they began in-depth observations of two sources initially flagged in 2016 and 2018 within the Gaia data. Utilizing space-based UV/X-ray missions and ground-based spectroscopy, they measured crucial physical parameters, which first hinted at something truly extraordinary.
Further confirmation arrived in 2023 when the Zwicky Transient Facility—an observatory scanning the entire Northern sky every two days with a wide-field camera—published data on a third, similar event. This solidified their confidence that they had indeed uncovered a rare and novel class of transient phenomena.
While astronomers have previously witnessed stars being ripped apart in ‘tidal disruption events’ (TDEs) — instances where a star’s material is torn by a black hole’s gravity, releasing energy comparable to over a hundred supernovae — ENTs, though sharing similarities like extreme temperatures, intense emissions, and broad spectral lines, are fundamentally distinct.
Dr. Hinkle clarified that the galaxies hosting ENTs are significantly larger than those associated with TDEs, typically featuring more massive central black holes. ENTs are also considerably rarer than the TDEs observed in our immediate cosmic neighborhood. However, current theories suggest that ENTs might simply be TDEs involving exceptionally massive stars, which are simply too scarce to be frequently detected close by.
Furthermore, ENTs are distinct from the enigmatic ‘fast X-ray transients’ (FXTs), which are brief bursts of X-rays originating from distant galaxies. These phenomena have baffled astronomers since their initial discovery in the 1970s, primarily because their signals are less energetic and more transient than the X-ray emissions from typical GRBs, making their origins particularly difficult to pinpoint.
It has since been discovered that when high-energy particle jets successfully pierce through a star’s outer layers, they generate GRBs. Conversely, if these jets are confined within the star, they release less energetic X-ray signals, which we perceive as FXTs. Therefore, unlike ENTs, FXTs are fundamentally a short-duration X-ray event.
Shedding Light on Cosmic Extremes
Astronomers are understandably thrilled by the prospect of studying the universe through the incredible luminosity of ENTs.
Dr. Hinkle noted, “By accumulating a diverse sample of ENTs, we gain a unique opportunity to investigate massive black holes in the early universe, particularly the vast majority that aren’t actively consuming matter. This serves as an invaluable addition to existing research on active, accreting black holes from that epoch.”
This ambitious research will be significantly advanced by upcoming technologies: a new generation of telescopes and instruments equipped with AI-powered data analysis. Projects like the Vera C. Rubin Observatory in Chile and the Nancy Grace Roman Space Telescope, set for launch in 2027, are poised to fundamentally transform our comprehension of the extreme physics governing a universe brimming with cosmic destruction on truly monumental scales.
Prakash Chandra is a science writer.