A sudden blast of gamma rays that swept past Earth in December 2004 is helping solve one of astrophysics’ biggest mysteries: where the universe’s heaviest elements—like gold and platinum—come from.

At the time of the Big Bang, the universe contained only the lightest elements: hydrogen, helium, and a dash of lithium. Heavier elements like iron were later forged in the hearts of stars. But elements heavier than iron? That’s been a trickier puzzle.

A rare type of event

“It’s a pretty fundamental question in terms of the origin of complex matter in the universe,” said Anirudh Patel, a doctoral student at Columbia University in New York. “It’s a fun puzzle that hasn’t actually been solved.”

During the 2004 event, detectors aboard NASA and ESA spacecraft caught a powerful gamma-ray flash. Ten minutes later, a weaker signal arrived—but its origin remained unknown. That is, until now.

Re-examining two decades of satellite data, scientists have traced the burst back to magnetar SGR 1806-20, a neutron star with a magnetic field a trillion times stronger than Earth’s. Magnetars occasionally undergo “starquakes” that unleash staggering energy—more than the Sun emits in a million years, all in less than a second. The findings, published in The Astrophysical Journal Letters, indicate that giant magnetar flares may account for up to 10% of every element heavier than iron in the Milky Way.

“This is really just the second time we’ve ever directly seen proof of where these elements form,” the first being neutron star mergers, says study co-author Brian Metzger, a senior research scientist at the Flatiron Institute’s Center for Computational Astrophysics and a professor at Columbia University. “It’s a substantial leap in our understanding of heavy elements production.”

Piecing together evidence

In 2024, Metzger and two colleagues published a paper in the Monthly Notices of the Royal Astronomical Society which calculated the impact of a magnetar giant flare on a neutron star crust and the associated baryon mass ejection into space, where heavy elements could form.

Neutron stars form after massive stars explode, leaving cores so dense that a teaspoon of their material would weigh a billion tons. A magnetar is an even more extreme variety wrapped in a magnetic field trillions of times stronger than Earth’s. On rare occasions, when that field twists, the star’s crust can snap in a “starquake,” releasing as much energy in a fraction of a second as the Sun radiates in a million years.

In this latest find, the team compared theoretical models with archival readings from the ESA’s recently retired INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) observatory and two NASA satellites, RHESSI and the Wind craft.

Their calculations suggest the flare forged roughly two million billion billion (not a typo) kilograms of heavy elements—about one-third of Earth’s mass—and scattered the material into interstellar space at a tenth the speed of light. The giant flares create unstable and heavy radioactive nuclei that decay into stable elements such as gold. If similar flares occur across the galaxy a few times each century, they could seed young stellar systems long before slower neutron-star collisions begin to enrich the cosmos.

“Magnetar giant flares could be the solution to a problem we’ve had where young galaxies show more heavy elements than mergers alone can explain,” Patel said.

NASA’s Compton Spectrometer and Imager (COSI), scheduled for launch in 2027, will survey the sky for the tell-tale gamma-ray fingerprints of freshly minted metals. Giant flares are rare in any single galaxy but should occur about once a year somewhere in the observable universe. COSI will be able to identify individual elements created in these events, providing a new understanding of the origin of the elements.

Researchers will also follow up on other archival data to see if other secrets are hiding in observations of other magnetar giant flares.

“It’s pretty incredible to think that some of the heavy elements all around us, like the precious metals in our phones and computers, are produced in these crazy extreme environments,” Patel said.