New Theory Suggests Heavy Elements May Form in Gamma-Ray Burst Jets

[frankerkanol]

One of the biggest mysteries in physics is understanding how the universe's heaviest elements, such as uranium and plutonium, are created. In a groundbreaking study, a team led by Los Alamos National Laboratory researchers is exploring an uncharted territory: the jets and cocoons formed during gamma-ray bursts from collapsing stars.

As outlined in a new paper published in The Astrophysical Journal, the researchers propose that high-energy photons deep within these jets can dissolve a star’s outer layers into neutrons, triggering a cascade of reactions that could lead to the formation of heavy elements.

"The creation of heavy elements like uranium and plutonium requires extremely rare and extreme conditions," said Matthew Mumpower, a physicist at Los Alamos. "We propose a new mechanism where neutrons are generated dynamically inside the star rather than existing beforehand."

Because free neutrons decay quickly—within about 15 minutes—scenarios with enough neutrons to create heavy elements are rare. The key process for forming the heaviest elements is known as the rapid neutron-capture process, or r-process, responsible for producing all naturally occurring thorium, uranium, and plutonium.

The new framework tackles the complex physics of the r-process by introducing a fresh scenario in which heavy elements can form during the violent collapse of massive stars.

Beyond providing insights into cosmic element formation, the study also offers valuable information for multiphysics simulations, neutron transport research, and the observation of rare astrophysical events—all of which have applications in national security.

A Jet Blasting Through a Star

Mumpower's proposed scenario begins with a massive star nearing the end of its life, depleted of nuclear fuel. As gravity overwhelms it, a black hole forms at the star's core. If the black hole spins rapidly, its intense gravitational field twists magnetic fields around it, launching a high-speed jet.

As the jet carves through the star, it creates a hot cocoon of material around itself, similar to a freight train plowing through snow, according to Mumpower. At the boundary where the jet meets stellar material, high-energy photons interact with atomic nuclei, converting protons into neutrons.

Additionally, some atomic nuclei break apart into individual protons and neutrons, producing even more free neutrons. The team's calculations suggest this neutron creation process can happen extremely quickly, within nanoseconds.

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Charged protons remain trapped by the magnetic fields in the jet, but the neutral neutrons escape into the surrounding cocoon. Having experienced a relativistic shock, these neutrons become densely packed, providing ideal conditions for the r-process to occur, forging heavy elements that are eventually expelled into space.

This complex series of reactions involves a wide range of physics disciplines, touching on atomic physics, nuclear physics, hydrodynamics, and general relativity—a true multiphysics challenge.

Despite these exciting findings, challenges remain. Many of the heavy isotopes predicted to form through the r-process have never been created or observed on Earth, meaning their properties—such as atomic mass and half-life—remain largely unknown.

Nevertheless, this new theory opens promising new paths for understanding the cosmic origins of the universe’s heaviest elements.