# How Gamma-Ray Bursts Work > On 23 October 2026 NASA ended the science mission of its Neil Gehrels Swift Observatory: after 22 years and more than 2,000 gamma-ray bursts, atmospheric drag had pulled it too low, and a robotic rescue failed in August. This film explains what Swift was built to catch: how satellites watching for nuclear tests found mysterious gamma-ray flashes in 1967; why bursts arriving from every direction pointed beyond our galaxy; how afterglows discovered in 1997 revealed distances of billions of light-years; why bursts come in long and short kinds; how narrow jets from collapsing giant stars make the long ones; how Swift's autonomous telescopes chased them; how a gravitational wave in 2017 proved that colliding neutron stars make short bursts and forge gold; the record-breaking burst of 2022; and what a burst could do to Earth. Interactive film: https://www.planetpast.com/stories/how-gamma-ray-bursts-work/ Publisher: PlanetPast (https://www.planetpast.com/) · d => T('readPublished', l, { d: dateIn(d, l) }) 2026-10-29 · Space, Physics ## Prologue ### The brightest flashes in the universe *Space · Physics* What gamma-ray bursts are, and how we learned it. About once a day, somewhere in the sky, a flash of gamma rays outshines every other gamma-ray source. For twenty-two years NASA's Swift observatory raced to catch them. On 20 October 2026 it made its last observation. Even that high there is a thin trace of air, and an active Sun made its drag stronger. Swift sank to about two hundred and seventy-five kilometres, too low to hold its telescopes steady. A robotic rescue craft failed in August, and Swift is expected to burn up within weeks. Planned for two years, it worked for twenty-two and caught more than two thousand bursts. This film explains what they are, and how we found out. - A flash found by spy satellites - Near or billions of light-years away? - Collapsing stars and colliding stars - What a burst could do to Earth - **20 Oct 2026**: Swift’s final observation - **~600 km**: at launch, November 2004 - **~275 km**: October 2026 - 3 Jul 2026: Rescue craft launched - 19 Aug: Boost attempt fails - 20 Oct: Last observation - 23 Oct: NASA ends the mission - **2,000+**: gamma-ray bursts - **1,400+**: supernovae studied - **~7,000**: papers using its data Prologue #### Swift’s last weeks NASA Science, 23 October 2026: Swift, launched on 20 November 2004, made its last observation on 20 October; orbiting less than 275 km up, it met too much drag to observe steadily and is expected to re-enter within weeks. It observed more than 2,000 gamma-ray bursts and more than 1,400 supernovae, and its data went into about 7,000 papers. Live Science: intense solar activity increased atmospheric drag; a private boost mission costing about $30 million failed in August. Wikipedia, Swift: the original orbit was about 585 × 604 km; Katalyst Space Technologies’ LINK spacecraft launched on 3 July 2026, and on 19 August the company said it could not rendezvous because of attitude-control problems; NASA terminated operations on 23 October 2026. Swift was planned for a two-year primary mission. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [NASA Science (23 Oct 2026, updated 26 Oct): NASA’s Swift mission ends, leaves behind scientific bonanza](https://science.nasa.gov/missions/swift/nasas-swift-mission-ends/); [Live Science (26 Oct 2026): NASA’s Swift observatory ends 22-year mission to study the most powerful explosions since the Big Bang](https://www.livescience.com/space/space-exploration/nasas-swift-observatory-ends-22-year-mission-to-study-the-most-powerful-explosions-since-the-big-bang); [Wikipedia: Neil Gehrels Swift Observatory](https://en.wikipedia.org/wiki/Neil_Gehrels_Swift_Observatory) ## Chapter I · A flash from nowhere ### A flash from nowhere *Chapter I* Found while watching for bombs. The story begins in the Cold War. In the 1960s the United States put the Vela satellites in orbit to check that no one was testing nuclear weapons in space, which gives off a flash of gamma rays. On 2 July 1967 they recorded a gamma-ray flash, but it looked nothing like a bomb. More followed, from random parts of the sky. The results stayed secret until 1973, when a team at Los Alamos led by Ray Klebesadel published them. Gamma-ray bursts had been discovered, and nobody knew what they were. - **γ**: gamma rays from a nuclear test ![A 1960s data room: a single sharp spike, unlike any bomb. AI-generated illustration.](https://assets.planetpast.com/a/39/39ee265e7ba141d4.jpg) - 2 Jul 1967: First burst recorded by Vela - 1973: Klebesadel’s team publishes Chapter I · A flash from nowhere #### Discovered by accident Wikipedia, gamma-ray burst: the Vela satellites, built to detect nuclear weapons tests, first recorded a gamma-ray burst on 2 July 1967; a Los Alamos team led by Ray Klebesadel analysed the data and published the discovery in 1973. NASA Imagine the Universe: the US Air Force’s Vela satellites monitored compliance with the nuclear test ban, and the discovery was not published until 1973 because of security concerns. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst); [NASA Imagine the Universe: gamma-ray bursts (Swift education pages)](https://imagine.gsfc.nasa.gov/educators/programs/swift/mission/grbs.html) ### Gamma rays are light, but of the highest energy there is: beyond ultraviolet, beyond X-rays, with each particle of light carrying far more energy than visible light. Our atmosphere absorbs most X-rays and gamma rays. That protects us, but it means these bursts can only be seen from above the air, by balloons, rockets and satellites. Send each kind of light down and see what reaches the ground. - Radio - Infrared, visible, ultraviolet - X-rays - Gamma rays: the highest $$E = h f$$ - $h$: Planck’s constant - $f$: frequency: highest for gamma rays - **above the air**: balloons, rockets or satellites ![A research balloon reaches about forty kilometres, above ninety-nine per cent of the atmosphere but not above all of it. AI-generated illustration.](https://assets.planetpast.com/a/ce/cee9a59478823cc0.jpg) - **Vela · BATSE · Swift**: all worked from orbit, above the absorbing air Chapter I · A flash from nowhere #### Light we cannot see from the ground NASA Imagine the Universe: “Earth’s atmosphere absorbs most X-rays and gamma-rays, so we need to put our telescopes and detectors above most of the Earth’s atmosphere”, using rocket flights, scientific balloons and satellites. A photon’s energy is E = hf; gamma rays lie at the top of the electromagnetic spectrum, above X-rays. Try it: radio and visible light reach the ground in the model; X-rays and gamma rays are stopped high in the atmosphere. Heights are schematic. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [NASA Imagine the Universe: observatories across the electromagnetic spectrum, technology](https://imagine.gsfc.nasa.gov/observatories/technology) ## Chapter II · Near or far? ### Near or far? *Chapter II* Where they come from tells us how far. For twenty years, the big question was distance. Were the bursts small events nearby, inside our own galaxy, or huge ones very far away? In 1991 NASA's Compton Gamma Ray Observatory began mapping them with an instrument called BATSE. If bursts came from our galaxy, they should crowd along the band of the Milky Way. They did not. Bursts came evenly from every direction. The Sun sits far from the centre of the Milky Way, so bursts from inside it would show up as a band. An even sky pointed far beyond it, though without a measured distance nothing was settled. Compare the two maps. - Nearby and modest: inside our galaxy - Far and enormous: other galaxies ![The whole sky flattened into an oval, with the Milky Way across the middle. AI-generated illustration.](https://assets.planetpast.com/a/d1/d1e1eea3c59f0eef.jpg) - **isotropic**: no crowding along the Milky Way’s plane > Without GRB distance measurements, it was impossible to rule out either theory. (NASA Imagine the Universe, on the BATSE years) Chapter II · Near or far? #### The map that pointed outward Wikipedia, gamma-ray burst: BATSE, on the Compton Gamma Ray Observatory launched in 1991, found that bursts were distributed isotropically on the sky, which supports an origin beyond the Milky Way. NASA Imagine the Universe: within a few years BATSE had recorded several hundred bursts; they were not concentrated in the Milky Way’s plane and arrived from all directions, which weakened the idea that they came from neutron stars in our galaxy, but without distance measurements astronomers could not rule out nearby origins such as the Oort cloud. Try it: “if from our galaxy” crowds the bursts along the Milky Way; “as observed” spreads them over the whole sky. The dots are illustrative, not BATSE’s catalogue. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst); [NASA Imagine the Universe: gamma-ray bursts (Swift education pages)](https://imagine.gsfc.nasa.gov/educators/programs/swift/mission/grbs.html) ### The answer came in 1997. The Italian-Dutch satellite BeppoSAX caught a burst and quickly pinned down its position, and telescopes found a fading glow at that spot, in X-rays and then in visible light. This afterglow is made by debris from the explosion, moving at nearly the speed of light, slamming into the gas around it. It lasts hours to days, long enough to study. Light from far away is stretched to longer, redder wavelengths as the universe expands, and measuring that redshift in the spectrum gave a distance. A burst in May 1997 lay about six billion light-years away. To look so bright from so far, the bursts had to be unimaginably powerful. - seconds: the gamma-ray flash itself - hours: X-ray afterglow - hours–days: visible light, then radio ![Robotic telescopes now swing onto a burst alert in under a minute, with no astronomer in the loop. AI-generated illustration.](https://assets.planetpast.com/a/a5/a5562a5f2e43e0df.jpg) ![Once a position was known, big telescopes could find the fading spot. AI-generated illustration.](https://assets.planetpast.com/a/89/894607ed00e52858.jpg) - **z = 0.835**: redshift: how much its light was stretched - **~6 billion ly**: distance - **GRB 970228**: X-ray and visible afterglows found with BeppoSAX Chapter II · Near or far? #### The afterglow gives the distance Wikipedia, gamma-ray burst: in 1997 BeppoSAX detected the X-ray and optical afterglows of GRB 970228; GRB 970508 then gave a redshift of z = 0.835, about 6 billion light-years. Afterglows arise when matter moving at close to the speed of light drives shock waves into the surrounding gas, producing synchrotron emission from X-rays to radio. NASA Imagine the Universe: afterglow discoveries from 1997 enabled redshift measurements, and every burst with a measured redshift lies at a cosmological distance. On screen: the shell of debris glows in turn in X-rays (blue), visible light (white) and radio (red) as it slows. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst); [NASA Imagine the Universe: gamma-ray bursts (Swift education pages)](https://imagine.gsfc.nasa.gov/educators/programs/swift/mission/grbs.html) ## Chapter III · Beams of light ### Beams of light *Chapter III* Short bursts and long ones. Bursts also come in two kinds. About seventy per cent are long, lasting more than about two seconds, typically half a minute. The rest are short: most are over in a fraction of a second. Two kinds of burst hinted at two kinds of cause. And the energy was staggering: if a long burst shone equally in all directions, matching it would take the Sun hundreds of billions of years. Watch the brightness of a short burst and a long one, second by second. - Long (> ~2 s, mean ~30 s): ~70% - Short (< ~2 s, typically ~0.3 s): ~30% - **~2 s**: shorter: “short”; longer: “long” - **10⁵³ erg**: a long burst, assuming equal brightness everywhere - **~880 billion years**: for the Sun to give out as much - **~10 billion years**: the Sun’s whole expected lifetime - Across: time in seconds - Up: gamma-ray brightness - Spiky and irregular, never the same twice Chapter III · Beams of light #### Short and long Wikipedia, gamma-ray burst: bursts shorter than about 2 seconds are classed as short (about 30% of events, typically about 0.3 s) and longer ones as long (about 70%, mean around 30 s). NASA Imagine the Universe: if long bursts emitted equally in all directions they would release about 10⁵³ erg; the Sun emits about 4 × 10³³ erg per second (NASA rounds this to 10³³), and NASA gives roughly 880 billion years to match one burst, against the Sun’s expected lifetime of about 10 billion years. Try it: the light curves are illustrative shapes, not real bursts. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst); [NASA Imagine the Universe: gamma-ray bursts (Swift education pages)](https://imagine.gsfc.nasa.gov/educators/programs/swift/mission/grbs.html) ### Part of the answer is that the energy is not spread evenly. Afterglows show that it is squeezed into two narrow jets, each opening at an angle estimated at between about two and twenty degrees, shooting out in opposite directions at almost the speed of light. So we only see a burst when one of its jets happens to point at Earth. For every burst we catch, many more are aimed elsewhere. Change the width of the jets and see how often one points our way. - **2°–20°**: estimated from “jet breaks” in afterglows ![Because the energy is beamed, the true output is often a few hundred times smaller than the all-sky figure. AI-generated illustration.](https://assets.planetpast.com/a/2a/2a9e8bc4a3be659f.jpg) $$f = 1 - \cos\theta$$ - $\theta$: the jet angle, measured from its axis - 2° jets: about 1 in 1,600: 0.06% - 10° jets: about 1 in 66: 1.5% - 20° jets: about 1 in 17: 6% - **most**: of all bursts point away and are never seen from Earth Chapter III · Beams of light #### Beamed, not spherical Wikipedia, gamma-ray burst: the emission is collimated into ultrarelativistic jets; jet angles estimated from afterglow “jet breaks” range from about 2 to 20 degrees. Taking θ as the angle from the jet’s axis, as in Frail et al. (2001), the share of the sky covered by two opposite cones is 1 − cos θ: about 0.06% for 2°, 1.5% for 10° and 6% for 20° (simple geometry). Beaming means the true energy is far smaller than the 10⁵³ erg of the equal-in-all-directions estimate, and that most bursts are never seen from Earth. Try it: the jets swing to random directions; the readout counts how many times one points at Earth. Widths in the model are exaggerated so they can be seen. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst); [Frail et al. (2001), Beaming in gamma-ray bursts: evidence for a standard energy reservoir (arXiv)](https://arxiv.org/abs/astro-ph/0102282v1) ### What makes the long bursts? The leading explanation is called a collapsar. A very massive star runs out of fuel and its core collapses into a black hole. Matter swirling into the young black hole drives two jets that bore out through the star in seconds. When a jet breaks the surface and points at us, we see a long burst. The evidence came in 1998, when a burst was found together with an unusual supernova, the explosion of a star, called SN 1998bw. Run the collapse. - A very massive star runs out of fuel - Its core collapses to a black hole - Infalling matter powers two jets - **> ~40 M☉**: mass suggested for stars that end this way ![A supernova can outshine every other star in its galaxy put together, for weeks, before it fades. AI-generated illustration.](https://assets.planetpast.com/a/d4/d425e50b3cbe27fa.jpg) ![GRB 980425 and SN 1998bw: one event seen two ways. AI-generated illustration.](https://assets.planetpast.com/a/5a/5a31fa65c0ec52c0.jpg) Chapter III · Beams of light #### When a giant star dies Wikipedia, gamma-ray burst: the collapsar model links long bursts to massive stars whose cores collapse into black holes; the association of GRB 980425 with supernova SN 1998bw supports it, although that burst was far less energetic than the average one. NASA Imagine the Universe: exceptionally massive stars, above about 40 solar masses, may collapse in explosions (hypernovae) roughly 100 times more energetic than a typical supernova, which may produce long bursts. Try it: the model shows the core collapsing and two jets drilling out of the star; sizes and times are schematic. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst); [NASA Imagine the Universe: gamma-ray bursts (Swift education pages)](https://imagine.gsfc.nasa.gov/educators/programs/swift/mission/grbs.html) ## Chapter IV · Swift ### Swift *Chapter IV* A telescope that turns itself. Afterglows fade fast, so in 2004 NASA launched a satellite built for speed: Swift, later named after its first lead scientist, Neil Gehrels. Its Burst Alert Telescope watches a wide patch of sky through a mask of fifty-two thousand lead tiles. The shadow a burst casts through the mask gives its rough position within about fifteen seconds. Then, with no one on the ground giving the order, Swift turns itself, and points its X-ray and ultraviolet-optical telescopes at the spot, narrowing the position to a few arcseconds, where one arcsecond is a three-thousand-six-hundredth of a degree. Trigger a burst. - **20 Nov 2004**: Delta II, Cape Canaveral - **2 years**: planned primary mission - **52,000**: lead tiles in its coded mask - **~15 s**: to a first position ![Gamma rays cannot be focused by any lens, so the instrument reads the shadow the mask throws and works backwards to the sky. AI-generated illustration.](https://assets.planetpast.com/a/88/88864d8ae2c3ff53.jpg) - BAT (hard X-rays): 60–240″ - XRT (X-rays): ~4″ - UVOT (UV and visible): ~1″ - 9 May 2005: first short burst with an accurately identified location - From then on: arcsecond positions within minutes Chapter IV · Swift #### Built for speed Wikipedia, Swift: launched on 20 November 2004 on a Delta II from Cape Canaveral. The Burst Alert Telescope (15–150 keV) uses a coded-aperture mask of 52,000 lead tiles over a cadmium-zinc-telluride detector and gives a position within 15 seconds to 1–4 arcminutes. Momentum wheels let Swift slew autonomously toward a burst; the X-Ray Telescope (0.2–10 keV) refines the position to about four arcseconds and the 30 cm Ultraviolet/Optical Telescope to about one arcsecond. GRB 050509B (9 May 2005) was the first short-duration burst with an accurately identified location; GRB 080319B (19 March 2008) was briefly visible to the naked eye at about 7.5 billion light-years; GRB 090423 (23 April 2009) lay about 13.035 billion light-years away. NASA Science: Neil Gehrels was the mission’s first principal investigator, and NASA renamed it for him in 2018. Try it: a burst appears, the wide-field telescope spots it and Swift swings round to point at it. Turning speed is not to scale. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: Neil Gehrels Swift Observatory](https://en.wikipedia.org/wiki/Neil_Gehrels_Swift_Observatory); [NASA Science (23 Oct 2026, updated 26 Oct): NASA’s Swift mission ends, leaves behind scientific bonanza](https://science.nasa.gov/missions/swift/nasas-swift-mission-ends/); [NASA Goddard: Swift’s key discoveries](https://swift.gsfc.nasa.gov/about_swift/discoveries.html) ### Because bursts are so bright, they can be seen across most of the universe. In April 2009 Swift caught one whose light had travelled for about thirteen billion years, from when the universe was young. In March 2008, another, about seven and a half billion light-years away, was briefly bright enough to see without a telescope. Swift's sharp positions also showed which galaxies the short bursts come from, and that evidence began to point to a different cause from dying giant stars: pairs of neutron stars colliding. - GRB 970508 (1997): ~6 - GRB 080319B (2008): 7.5 - GRB 090423 (2009): 13.0 ![For under a minute in 2008, a point of light from 7.5 billion light-years away. AI-generated illustration.](https://assets.planetpast.com/a/21/21ac1346c8e6ac18.jpg) - **host galaxies**: found once XRT and UVOT gave arcsecond positions Chapter IV · Swift #### Seeing across the universe Wikipedia, Swift: GRB 090423 (23 April 2009) was, at the time, the most distant cosmic explosion seen, at about 13.035 billion light-years; GRB 080319B (19 March 2008) was bright enough to be briefly visible to the naked eye, at about 7.5 billion light-years. NASA Goddard, Swift’s key discoveries: GRB 090423 at redshift 8.3 was the most distant spectroscopically confirmed object known; arcsecond positions from XRT and UVOT allowed the host galaxies of short bursts to be identified, strengthening the case for merging neutron stars. Wikipedia, GRB 221009A: about 2.4 billion light-years away. On screen: each burst on a line of distance, drawn logarithmically, with our galaxy at the start. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: Neil Gehrels Swift Observatory](https://en.wikipedia.org/wiki/Neil_Gehrels_Swift_Observatory); [NASA Goddard: Swift’s key discoveries](https://swift.gsfc.nasa.gov/about_swift/discoveries.html); [Wikipedia: GRB 221009A](https://en.wikipedia.org/wiki/GRB_221009A) ## Chapter V · Colliding stars ### Colliding stars *Chapter V* A ripple in space, then a flash. Short bursts had a suspect: neutron stars, the ultra-dense collapsed cores left behind when massive stars explode. Two of them orbiting each other slowly spiral together. On 17 August 2017, the LIGO and Virgo detectors felt the ripples in space, gravitational waves, from such a merger. About 1.7 seconds later, two gamma-ray satellites, NASA's Fermi and Europe's INTEGRAL, recorded a short gamma-ray burst from the same part of the sky. Telescopes then found a glowing cloud of debris in a galaxy a hundred and thirty million light-years away, rich in newly made heavy elements, including gold. Run the merger. - The collapsed core of a dead star - Left behind when a massive star explodes - Pairs spiral in as they lose energy - 0 s: Gravitational waves: LIGO and Virgo - +1.7 s: Short burst GRB 170817A: Fermi, INTEGRAL - +11 h: Glowing debris found in NGC 4993 - **NGC 4993**: an elliptical galaxy about 130 million light-years away ![The debris cloud forged heavy elements: an estimated ten Earth masses of gold and platinum. AI-generated illustration.](https://assets.planetpast.com/a/0d/0de5078faf7f1abd.jpg) - **~10⁻¹⁵**: largest possible gap between its speed and light’s, as a fraction Chapter V · Colliding stars #### A collision seen two ways Wikipedia, GW170817: LIGO and Virgo detected the gravitational wave on 17 August 2017, produced by two neutron stars merging in the galaxy NGC 4993, about 130 million light-years (40 Mpc) away. The short burst GRB 170817A was detected by Fermi and INTEGRAL about 1.7 seconds later, confirming that neutron star mergers produce short gamma-ray bursts. About 11 hours later an optical transient, a kilonova, was found; its r-process nucleosynthesis made an estimated 16,000 Earth masses of heavy elements, including about 10 Earth masses of gold and platinum. The difference between the speed of gravitational waves and of light was constrained to about one part in 10¹⁵. Try it: the two stars spiral in, merge, flash and leave a glowing cloud. Orbits and sizes are schematic. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: GW170817](https://en.wikipedia.org/wiki/GW170817); [NASA Goddard: Swift’s key discoveries](https://swift.gsfc.nasa.gov/about_swift/discoveries.html) ## Chapter VI · The brightest of all ### The brightest of all *Chapter VI* Felt in Earth’s upper atmosphere. On 9 October 2022, Swift and NASA's Fermi telescope caught the brightest gamma-ray burst ever recorded. Astronomers nicknamed it the BOAT: the brightest of all time. It came from about two point four billion light-years away, close for a burst. Its gamma rays even disturbed Earth's ionosphere, the electrically charged upper atmosphere, for several hours. By one estimate, a burst this bright, seen from Earth, comes once in ten thousand years. And it was two point four billion light-years away. So what would a burst much closer do? - **9 Oct 2022**: seen by Swift and Fermi - **Sagitta**: the constellation it came from - **afterglow**: the brightest ever seen, beating GRB 030329 - **2.4 billion ly**: distance - **z = 0.151**: redshift - Ionosphere disturbed for several hours - Picked up by lightning detectors in India and Germany - Compared by a solar physicist to a major solar flare - **1 in 10,000 years**: estimated, from brightness and distance Chapter VI · The brightest of all #### The BOAT Wikipedia, GRB 221009A: detected on 9 October 2022 by Swift and the Fermi Gamma-ray Space Telescope, from the constellation Sagitta, about 2.4 billion light-years away (redshift 0.151). It is considered the brightest gamma-ray burst ever recorded, nicknamed “BOAT”, with the brightest afterglow ever seen. It had the strongest effect on Earth’s atmosphere of any burst on record: lightning detectors in India and Germany registered a mild disturbance of the ionosphere lasting several hours; a solar physicist compared its imprint to that of a major solar flare. From its brightness and proximity it is estimated to be a once-in-10,000-year event. On screen: the burst’s gamma rays reach the day side of Earth and light up the ionosphere; the colours are illustrative. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: GRB 221009A](https://en.wikipedia.org/wiki/GRB_221009A) ### Could one harm us? Only if it were close and aimed straight at Earth. A burst within several thousand light-years, pointed our way, could strip away part of the ozone layer and let in more of the Sun's ultraviolet light. Some scientists have suggested such a burst may have played a part in a mass extinction about four hundred and fifty million years ago, but that is a hypothesis, not an established finding. In a galaxy like ours, long bursts are estimated to happen once every ten thousand to a million years, and most point elsewhere. Compare a burst far away with one nearby. ![A barred spiral about 100,000 light-years across; the Sun lies in a spiral arm. AI-generated illustration.](https://assets.planetpast.com/a/38/381eb96e6ee33cda.jpg) - **1 kpc ≈ 3,260 ly**: the unit astronomers use for such distances - Nearby aimed burst could thin the ozone: modelled - Ordovician extinction link: a hypothesis - Low estimate: 10,000 - High estimate: 1,000,000 Chapter VI · The brightest of all #### Should we worry? Wikipedia, gamma-ray burst: a burst within a few kiloparsecs (one kiloparsec is about 3,260 light-years) aimed at Earth could deplete the ozone layer and raise ultraviolet levels at the surface; the Late Ordovician mass extinction, about 450 million years ago, has been suggested as possibly caused by one, which remains a hypothesis. For a galaxy the size of the Milky Way, estimates of the rate of long bursts range from one every 10,000 years to one every 1,000,000 years, and beaming means that most of them would not point at Earth. Try it: “far away” places a burst across the galaxy, “nearby” within several thousand light-years of the Sun; neither points at us in the model. The 3D scenes are teaching models, not to scale: stars, jets, satellites and distances are drawn so they can be seen together. Sources: [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst) ## Epilogue ### Flashes from the edge of time *Epilogue* Swift falls, the watch goes on. In under sixty years, a mysterious flash found by satellites watching for nuclear tests became one of the best-understood explosions in the universe: dying giant stars and colliding neutron stars, beaming their energy across billions of light-years. Swift will soon burn up, but the watch goes on. SVOM, a French and Chinese satellite launched in 2024, now turns itself towards each new flash, the way Swift did for twenty-two years. - 1967: Vela records the first burst - 1991: BATSE: bursts from every direction - 1997: Afterglows give distances - 1998: A burst with a supernova - 2004: Swift launched - 2017: Neutron star merger, waves and burst - 2022: The BOAT - 2026: Swift’s mission ends - **2,000+**: bursts caught in 22 years - **SVOM**: France and China, launched 22 June 2024 ![SVOM carries four instruments, two built in China and two in France. AI-generated illustration.](https://assets.planetpast.com/a/a3/a3cfddf123463b10.jpg) > All of the GRBs that have had their redshifts measured are at cosmological distances. (NASA Imagine the Universe) Epilogue #### Sources and notes Every figure in this film comes from the sources below, which were read for it. CEA Irfu: SVOM, a French–Chinese mission, launched on a Long March 2C from Xichang on 22 June 2024; its ECLAIRs gamma-ray detector spots bursts and reorients the satellite automatically. Energies, distances and rates are those quoted by the sources, and the 3D scenes are simplified teaching models, not to scale. All stills are AI-generated illustrations, not photographs. Sources: [NASA Science (23 Oct 2026, updated 26 Oct): NASA’s Swift mission ends, leaves behind scientific bonanza](https://science.nasa.gov/missions/swift/nasas-swift-mission-ends/); [Live Science (26 Oct 2026): NASA’s Swift observatory ends 22-year mission to study the most powerful explosions since the Big Bang](https://www.livescience.com/space/space-exploration/nasas-swift-observatory-ends-22-year-mission-to-study-the-most-powerful-explosions-since-the-big-bang); [Wikipedia: Neil Gehrels Swift Observatory](https://en.wikipedia.org/wiki/Neil_Gehrels_Swift_Observatory); [Wikipedia: gamma-ray burst](https://en.wikipedia.org/wiki/Gamma-ray_burst); [NASA Imagine the Universe: gamma-ray bursts (Swift education pages)](https://imagine.gsfc.nasa.gov/educators/programs/swift/mission/grbs.html); [NASA Imagine the Universe: observatories across the electromagnetic spectrum, technology](https://imagine.gsfc.nasa.gov/observatories/technology); [NASA Goddard: Swift’s key discoveries](https://swift.gsfc.nasa.gov/about_swift/discoveries.html); [Wikipedia: GW170817](https://en.wikipedia.org/wiki/GW170817); [Wikipedia: GRB 221009A](https://en.wikipedia.org/wiki/GRB_221009A); [CEA Irfu (June 2024): successful launch of the SVOM satellite](https://irfu.cea.fr/en/dap/2024/06/successful-launch-of-svom-satellite)