In an ejection that would have caused its rotation to slow, a magnetar is depicted losing material into space in this artist’s concept. The magnetar’s strong, twisted magnetic field lines (shown in green) can influence the flow of electrically charged material from the object, which is a type of neutron star. (Credit: NASA/JPL-Caltech)
In a nutshell
- Magnetar giant flares are now confirmed as a new source of heavy elements like gold, platinum, and uranium, thanks to a reanalysis of a mysterious gamma-ray signal from a 2004 space explosion.
- The delayed gamma-ray emission matched predictions for r-process nucleosynthesis, revealing that these rare stellar events can eject radioactive material that forges heavy elements as it decays.
- This discovery suggests magnetars may account for up to 10% of the universe’s heavy elements, reshaping our understanding of how the cosmos builds the raw materials that make up planets, electronics, and even life.
NEW YORK — The gold in your wedding ring may have come from a star’s explosive death. For decades, scientists have hunted for the factories that produce the universe’s heaviest elements, and now they’ve found an unexpected one: magnetar giant flares, cosmic explosions that release more energy in a millisecond than our Sun does in 100,000 years. Researchers have confirmed that these titanic blasts create the elements that make up our jewelry, electronics, and even our bodies.
The study, published in The Astrophysical Journal Letters, changes our understanding of where heavy elements like gold, platinum, and uranium come from. Until now, scientists thought only neutron star collisions could create these heavy elements, but this new discovery shows that magnetars, the universe’s most magnetic stars, also play a big role in making them.
The research team from various institutions reexamined a gamma-ray signal detected after a massive flare from the magnetar SGR 1806-20 in 2004. This signal, which had stumped astronomers for years, now appears to be direct evidence of radioactive decay from newly created heavy elements.
Explosive Alchemists
Magnetars are neutron stars with magnetic fields trillions of times stronger than Earth’s. When their magnetic fields reconfigure, they can produce giant flares that release enormous amounts of energy in seconds. The 2004 flare from SGR 1806-20 was so powerful that it measurably affected Earth’s upper atmosphere despite occurring about 30,000 light-years away.
Since the 1950s, scientists have known that about half the elements heavier than iron are created through the r-process, where atomic nuclei rapidly capture neutrons. But pinpointing where in the universe this happens has been challenging.
The research team found that during a magnetar giant flare, the tremendous energy released drives a shock wave into the neutron star’s crust. This shock heats and ejects material at about 10% the speed of light. Under these extreme conditions, neutrons rapidly combine with atomic nuclei to forge heavier elements, similar to what happens when neutron stars merge, but on a smaller scale.
Reinterpreting A Mystery Signal
By comparing the gamma-ray signal’s properties with theoretical predictions, the researchers concluded the flare produced about one-millionth of our Sun’s mass in r-process elements. While that might sound tiny, multiply this by the frequency of such flares across the universe, and magnetars could account for 1-10% of all r-process elements in our galaxy.
Although multiple space observatories detected this signal back in the early 2000s, its true nature wasn’t recognized until now. The scientists found that after the initial blast of gamma rays, a second wave of energy appeared about 7 minutes later, peaked between 10 and 13 minutes, and gradually faded over the next few hours. This pattern matches that of the radioactive decay of newly formed heavy elements.
Because magnetars form quickly after stars are born, they could have enriched the universe’s first galaxies with heavy elements much earlier than previously thought possible. Magnetars could also be major sources of r-process cosmic rays, high-energy particles composed of these heavy elements that travel through space.
NASA‘s upcoming Compton Spectrometer and Imager (COSI) mission, scheduled to launch in 2027, should be able to detect and characterize the r-process emission from future giant flares in much greater detail.
The team predicts that future galactic magnetar flares should also produce a brief optical/UV flash they’ve dubbed a “nova brevis” (“brief nova”) that could potentially be visible to the naked eye, though lasting only minutes. This would provide another means to study this process in action.
These stellar alchemists, with their unimaginable magnetic fields and explosive tantrums, are now confirmed contributors to Earth’s chemical inventory. When a magnetar flares, astronomers may be witnessing the birth of atoms that could one day form planets, technologies, or even life.
Paper Summary
Methodology
The researchers reanalyzed gamma-ray observations from multiple satellites (INTEGRAL SPI-ACS, Konus-WIND, and RHESSI) that detected a mysterious emission component following the December 2004 giant flare from magnetar SGR 1806-20. They compared the timing, brightness, decay rate, and spectral properties of this signal with theoretical predictions for gamma-ray emission from freshly synthesized r-process elements. Using the SkyNet nuclear reaction network, they calculated nucleosynthesis yields and resulting radioactive decay signals for ejecta with properties consistent with previous modeling of magnetar flares. They developed both analytic estimates and detailed numerical models accounting for nuclear decay lines, Doppler broadening due to ejecta velocity, and gamma-ray opacity effects to predict the expected gamma-ray emission.
Results
The analysis revealed that the delayed gamma-ray signal observed after the SGR 1806-20 giant flare matches theoretical predictions for r-process nucleosynthesis in both timing and spectral characteristics. The signal rose to peak brightness around 600-800 seconds after the initial flare, then decayed with a power-law rate proportional to t^(-1.2±0.1), consistent with radioactive decay of r-process elements. The inferred amount of r-process material produced was approximately 10^(-6) solar masses. The emission spectrum peaked around 1 MeV, matching the expected quasi-continuous spectrum from Doppler-broadened gamma-ray decay lines. Based on the rate of giant flares in the galaxy, the researchers estimate magnetars contribute approximately 1-10% of the total Galactic r-process element production.
Limitations
The researchers note that detailed features of the gamma-ray spectra are sensitive to the exact abundance yield and ejecta properties. Current observations lack the spectral resolution to identify individual decay-line features that would provide definitive “smoking gun” evidence for specific r-process isotopes. The theoretical model includes simplifications regarding the ejecta velocity distribution and opacity. There is uncertainty in translating the observed fluence to total r-process mass due to opacity effects and viewing angle considerations.
Funding/Disclosures
The research was supported by the National Science Foundation (AST-2009255), the NASA Fermi Guest Investigator Program (80NSSC22K1574), the Simons Foundation (through the Flatiron Institute), NSF grant PHY-2309135 to the Kavli Institute for Theoretical Physics, the Charles University Grant Agency (GA UK) project No. 81224, and a grant from the Simons Foundation (1161654) to the Aspen Center for Physics.
Publication Information
The paper titled “Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806–20 Magnetar Giant Flare” was authored by Anirudh Patel, Brian D. Metzger, Jakub Cehula, Eric Burns, Jared A. Goldberg, and Todd A. Thompson. It was published in The Astrophysical Journal Letters (Volume 984, L29) on April 29, 2025.
