In Simple Terms
Some distant cosmic events send out powerful flashes of light and energy that can last from seconds to hours. Scientists are learning that these explosions can happen in more ways than they once thought, and that they may help explain where elements such as gold come from. Each new discovery is revealing both how the universe works and how much remains unknown.
When Blips in Space Looked Like Nuclear Tests
Far out in the universe, a star may collapse or two incredibly dense stellar remnants may collide, sending out beams of radiation and particles moving almost as fast as light. If one of those beams points toward Earth, space observatories can detect a flash of gamma rays: extremely energetic radiation invisible to our eyes, but potentially the first sign of a violent cosmic explosion. After the flash, the surrounding region glows at other wavelengths, from X-rays to visible light and radio waves.
The discovery of these explosions did not begin with an observatory built to explore the distant universe. It began with a Cold War military program. In the 1960s, the United States launched the Vela satellites to monitor Earth for signs of nuclear weapons tests. On July 2, 1967, two satellites detected an unusual signal. At first, it looked like a possible nuclear explosion, but its radiation pattern did not match what scientists expected from a test on Earth. The signal also appeared to come from space.
When researchers examined the satellite data, they found 16 similar events recorded between July 1969 and July 1972. The information was initially kept secret. The findings were made public in 1973, after scientists confirmed that the signals did not point to a hidden Soviet test. At the time, no one had a clear explanation for the phenomenon, so researchers called the flashes gamma-ray bursts, or GRBs.
Over the following decades, space observatories—including NASA’s Compton Gamma Ray Observatory, the European INTEGRAL observatory, and NASA’s Fermi and Swift observatories—detected thousands of bursts. These observations showed that the signals were not from explosions on Earth or imagined sources; they were natural events happening in distant celestial objects. Today, observatories detect about one burst per day on average, although many go unnoticed because their beams are not aimed at us.
What Makes the Flashes So Powerful?
A gamma-ray burst does not release energy evenly in every direction. In the usual explanation of these events, two narrow, oppositely directed jets shoot out from near a black hole, carrying extremely hot material and fast-moving particles traveling close to the speed of light. Scientists think the particles may include electrons and positrons, and possibly protons, while magnetic fields help guide them. We usually see only a jet that happens to travel close to Earth’s line of sight.
The bursts vary in duration, and for many years scientists used a simple division: short events lasting no more than two seconds, and long ones lasting tens of seconds. Short bursts were generally linked to the mergers of two neutron stars—small, extraordinarily dense stellar remnants—while long bursts were associated with the collapse of a massive star. In either case, material can gather around the newly formed black hole, which may pull some of it in and eject some through its jets. The amount of available material, and how quickly it falls inward, affect how long the jets remain active.
In just seconds, a gamma-ray burst can release as much energy as the Sun produces over its entire lifetime. Another estimate compares the energy with roughly a million trillion trillion Hiroshima-sized bombs. These events are therefore more powerful than supernova explosions, even though supernovae are among the most energetic phenomena in the universe. The vast distances involved, however, weaken the signal that reaches Earth: most observed bursts come from galaxies billions of light-years away.
If a jet hit a planet directly from a distance of a few thousand light-years, the consequences for its atmosphere could be serious. Physicist and astronomer Brian Thomas of Washburn University has studied the possibility of such an impact on Earth. The radiation could break apart oxygen and nitrogen molecules and help create nitrogen oxides, which deplete ozone. If the ozone layer weakened for nearly a decade, living things could be exposed to more ultraviolet radiation. But this is a hypothetical scenario, and the chance of it happening is extremely small. It is not an everyday threat to us.
Cosmic Factories for the Elements Around Us
Gamma-ray bursts matter for another reason: they may reveal how some of the materials that make up our world came into existence. Through the reactions inside them, the first stars produced hydrogen, helium, and heavier elements up to iron. Creating many elements heavier than iron requires conditions rich in free neutrons. Atomic nuclei can capture these neutrons rapidly in a process known as rapid neutron capture, or the r-process.
Scientists think that about half of the elements heavier than iron form this way, including gold, platinum, uranium, thorium, and iodine. The right conditions may arise when two neutron stars collide, or during some especially violent stellar collapses. Observing a flash can therefore tell researchers more than where it came from: it can help them trace the origins of elements with very different roles. Iodine is part of thyroid hormones, uranium contributes to the heat inside Earth, and gold and platinum are important for cultural and industrial purposes.
A major piece of evidence arrived in 2017. On August 17, the American LIGO and Italian Virgo observatories detected ripples in spacetime coming from the galaxy NGC 4993, about 130 million light-years away in the constellation Hydra. The signal’s characteristics revealed that the two objects involved were neutron stars that had collided. Shortly afterward, NASA’s Fermi telescope detected a gamma-ray burst from the same direction, named GRB 170817A.
The event was accompanied by a glow known as a kilonova, associated with the ejection of neutron-rich material—a promising environment for making heavy elements. One calculation estimated that the amount of gold and platinum produced may have been equivalent to 10 times the mass of Earth. The observation did not settle every question. Its importance was that it brought gravitational waves, gamma rays, and the glow that followed together in a single event, offering strong support for the idea that neutron-star mergers forge some of the heaviest elements.
Long Bursts That Blurred the Lines
The rules seemed straightforward until an event appeared in December 2021. GRB 211211A was detected in a galaxy 1.1 billion light-years away and lasted about 50 seconds—a duration usually associated with long bursts caused by the collapse of a massive star. But a team that included astronomer Jillian Rastinejad of the University of Maryland, College Park, used observatories in Hawaii and Arizona and found none of the expected signs of a supernova. Instead, they observed a reddish glow that appeared consistent with the production of heavy elements in a kilonova.
The study, published in 2022, showed that the event did not follow the standard pattern expected from the collapse of a massive star, but its explanation remains debated. Perhaps two neutron stars merged, but the long burst raises a question: how could their remains have supplied fuel to jets for 50 seconds? One possibility is that a black hole tore apart a companion neutron star, producing a large amount of material that gradually fell into the black hole. Another idea is that a large disk of material formed around the merger’s remnant and kept feeding the jets. Astrophysicist Eric Burns of Louisiana State University, meanwhile, suggested that the second object might have been a white dwarf—a remnant of a smaller star like the Sun—which could take longer to be swallowed.
Then, in 2023, GRB 230307A lasted 200 seconds without showing clear signs of a supernova. Astronomers pointed the James Webb Space Telescope at its source and detected infrared light from tellurium, an element associated with the r-process. This strengthened the possibility that neutron stars were involved, but it did not explain how such a long burst was produced. Gravitational-wave observations might have helped identify the objects, but LIGO and Virgo were offline for maintenance at the time.
The Brightest Burst Still Has Secrets
On October 9, 2022, scientists detected another event that became known as the Brightest Of All Time, or BOAT. It came from 2.4 billion light-years away, and its beam struck Earth so powerfully that orbiting gamma-ray observatories were temporarily overwhelmed by the signal. The flow of gamma rays lasted more than 10 minutes. The event also affected the upper layers of Earth’s atmosphere, and disturbances were detected in radio communications and in lightning activity recorded by sensors in India.
Scientists believe the burst began when a star with a mass of up to about 30 times that of the Sun collapsed to form a black hole. Astronomers estimate that an event this powerful might reach Earth once every 10,000 years. Months after the burst, the James Webb Space Telescope identified the associated supernova. Scientists had hoped to find signs of heavy elements made by the collapsing star, but the observations revealed no clear evidence of them. The burst did not solve the mystery of where heavy elements come from. Instead, it raised a new question: do stellar collapses produce these elements in smaller quantities than scientists expected?
Seven Hours of Intermittent Radiation
On July 2, 2025, the Fermi telescope recorded a new event designated GRB 250702B, coming from a dusty galaxy about 8 billion light-years away. Its energy was estimated to be equivalent to the radiation produced by 1,000 Suns over 10 billion years. It was not brighter than BOAT, but it broke a record for duration: the burst lasted at least seven hours. It also appeared to fade and flare up again three times.
A single explosion from an ordinary star is difficult to reconcile with such a long event. One proposed idea is that the jet wobbled, moving into and out of our field of view so that its emission appeared to stop and start again. But that does not explain the duration. A faster-spinning collapsing star could slow the rate at which material falls into it, but if it spins too rapidly, it may not collapse in the required way. As a result, teams—including one led by graduate student Eliza Knights and Brian Thomas—have explored more unusual systems.
One model proposes a small black hole with about three times the Sun’s mass and a diameter of roughly 10 miles, orbiting a low-mass star. The black hole may initially have pulled hydrogen from the star, leaving behind a helium core, before sinking into the star and devouring and tearing apart its material. In this scenario, the star’s core collapses toward the black hole while jets shoot from its poles, pierce the star’s outer layers, and may cause the star to explode as a supernova. This is a possible explanation, not a settled conclusion. The event is unique so far, and a sample of one burst is too small to establish which model is right with confidence.
The Bottom Line
Gamma-ray bursts offer a view of extreme cosmic events, but they are more than distant flashes of light. They reveal how matter behaves near black holes, let scientists test ideas about the origins of heavy elements, and act as beacons for exploring ancient galaxies. Events such as the 2017 neutron-star merger have confirmed some scientific predictions. Bursts observed in 2021, 2023, and 2025, however, show that the traditional division between short and long events cannot explain everything astronomers see.
Researchers still face three interconnected challenges: understanding the violent physics that powers these explosions, building more capable observatories to capture their details, and working with the small number of rare events that can be studied closely. Some mysteries may remain open for years, but a single new observation could quickly change the picture. These events can last seconds—or, as one did, seven hours—and offer a rare chance to watch the universe change through our instruments.