The violent collision of two neutron stars hundreds of millions of years ago is providing Penn State scientists with new insights into how the universe’s heaviest elements were created.
At the center of the new research published in The Astrophysical Journal Letters was a brilliant flash picked up by NASA’s Fermi satellite, designated as GRB 230906A. The September 2023 flash observed by Fermi was a short gamma-ray burst, which is often produced when two neutron stars spiral and eventually collide.
Gamma-ray Bursts
Gamma-ray bursts are the brightest and most energetic explosions in the cosmos, capable of eclipsing entire galaxies with one flash. The enormous amount of energy released in these events forges some of the universe’s heaviest elements, like gold and platinum.
The Penn State team, led by Dr. Simone Dichiara, followed up on Fermi’s initial spotting with further observations on NASA’s Chandra X-ray Observatory and Hubble Space Telescope. Their subsequent observations located the gamma burst within a faint galaxy, itself part of a group 8.5 million light-years distant from Earth. Although the actual events may have occurred millions of years ago, the long-distance light travel is only now revealing to scientists some interesting activity as the group merges together.
Colliding Galaxies and Neutron Stars
As galaxies within the system interact and collide, star formation rates increase. These galactic collisions in GRB 230906A’s neighborhood have produced a debris field of gas and stars in which the neutron star impact took place. The debris field is known as a tidal tail, formed as the galaxy’s gravity rips stars and gas from one another, leaving behind a long string of material.
“This could be an indication that tidal interaction between galaxies can trigger star formation and two neutron stars that evolve from the new stars can end up merging into each other, making these big explosions and energetic emissions that we observe,” Dichiara said.
Forged in a Neutron Star Merger
The bright halos of light produced in binary star mergers, known as kilonova emissions, are one of the universe’s foremost heavy element forges.
“This could provide a natural explanation for why we see an enhanced rate of production of heavy elements in the halo of interacting galaxies,” Dichiara said.
In fact, the team believes that 700 million years ago, this long-running galactic merger may have birthed the stars that collided in the event. That enormous explosion as the neutron stars met also pushed heavy elements into the surrounding space.
“We got a rare glimpse into how destruction can be a catalyst for creation,” said co-author Jane Charlton, professor of astronomy and astrophysics at Penn State. “The gold that we have on Earth was produced in an explosive event of this nature. The heavy elements in our body, like iron for example, come from about 10,000 stars that were in our galaxy and died. It took billions of years, but that iron persisted on Earth and, as our bodies formed and evolved, they used that material.”
Work Continues on the Neutron Star Collision
While the galaxy group itself is known to be located around 8.5 million light-years away, the precise location of the explosion itself remains undetermined. The possibility remains that the burst was even more than 8.5 million light-years away, making it the most distant gamma-ray burst ever documented. Hopefully, the precision of the next-generation of space observatories, as well as state-of-the-art ground-based telescopes, will help to answer these questions.
“It’s very common for galaxies to have neighbors. That’s not unusual at all, but having them collide is,” Clifton concluded. “Our own Milky Way galaxy has a neighbor, the Andromeda galaxy, and four or five billion years from now, it will merge with the Milky Way galaxy.”
“This very thing could be happening, and tidal tails will form, kicking up heavy elements and enriching the universe,” Clifton added.
The paper, “A Merger within a Merger: Chandra Pinpoints the Short GRB 230906A in a Peculiar Environment,” appeared in The Astrophysical Journal Letters on March 10, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.