A scientific investigation published in the Astrophysical Journal posits that intensely energetic photons, originating from the profound depths of gamma-ray burst jets emitted by a collapsing star, possess the capability to dismantle a star’s outer strata into unfettered neutrons. This phenomenon, in turn, initiates a cascade of physical transformations that culminate in the synthesis of substantial elements.
A high-energy photonic jet, depicted in white and blue, pierces through a collapsar featuring a central black hole. The surrounding red region signifies a cocoon where free neutrons might be ensnared, facilitating the r-process – the nucleosynthesis responsible for the creation of heavy elements. This imagery is provided courtesy of Los Alamos National Laboratory.
The genesis of the universe’s heaviest elements is contingent upon astrophysical environments characterized by an abundant supply of neutrons.
Within the cosmic expanse, neutrons can be found either sequestered within atomic nuclei or existing in a medium subjected to extreme pressures.
Independent neutrons are exceptionally scarce, owing to a fleeting half-life that spans less than fifteen minutes.
“The fabrication of ponderous elements such as uranium and plutonium is a process that mandates extraordinary cosmic conditions,” expounded Dr. Matthew Mumpower, a physicist affiliated with Los Alamos National Laboratory.
“The cosmos offers only a restricted number of plausible yet infrequently encountered scenarios wherein these elements can be forged, and all such loci necessitate a profusion of neutrons. Our hypothesis introduces a novel occurrence wherein these neutrons are not pre-existing but are instead generated dynamically within the stellar body.”
The pivotal mechanism for generating the most substantial elements on the periodic table is recognized as the rapid neutron-capture process, or r-process. It is currently believed to be the progenitor of all naturally occurring thorium, uranium, and plutonium observed throughout the universe.
The research team’s theoretical construct grapples with the intricate physics governing the r-process, proposing reactions and phenomena associated with stellar collapses that could precipitate the formation of heavy elements, thereby resolving these complexities.
Beyond elucidating the origins of heavy elements, the proposed framework offers solutions to critical inquiries concerning neutron propagation, sophisticated multiphysics simulations, and the detection of rare celestial events. These areas of research hold considerable significance for national security applications, which can benefit from the insights derived from this investigation.
In the scenario delineated by the researchers, a colossal star commences its demise as its internal nuclear fuel reserves are depleted.
Unable to counteract its own gravitational pull, a black hole materializes at the star’s core.
Should the black hole exhibit a sufficiently rapid rotation, the extreme gravitational forces proximate to it will induce frame-dragging, thereby twisting the magnetic field and launching a formidable jet.
Through a sequence of subsequent reactions, a broad spectrum of photons is generated, some of which possess exceedingly high energy.
“The jet propels itself through the star ahead of it, creating a heated cocoon of stellar matter enveloping the jet, analogous to a freight train plowing through a snowdrift,” remarked Dr. Mumpower.
At the interface where the jet impinges upon the stellar material, high-energy photons, in essence, light, can interact with atomic nuclei, transforming protons into neutrons.
Existing atomic nuclei may also be broken down into their constituent nucleons, thereby yielding additional free neutrons to fuel the r-process.
The team’s computational analyses indicate that the interaction between light and matter can generate neutrons with astonishing rapidity, on the order of nanoseconds.
Due to their electrical charge, protons become ensnared within the jet by the potent magnetic fields.
Neutrons, being electrically neutral, are propelled outward from the jet into the surrounding cocoon.
Having undergone a relativistic shock, the neutrons exhibit an exceptionally high density in comparison to the adjacent stellar material. Consequently, the r-process can commence, forging heavy elements and isotopes that are subsequently ejected into the cosmos as the star disintegrates.
The conversion of protons into neutrons, coupled with the egress of free neutrons into the surrounding cocoon to engender heavy elements, draws upon a comprehensive array of physical principles and encompasses all four fundamental forces of nature. This constitutes a genuine multiphysics challenge, integrating domains of atomic and nuclear physics with hydrodynamics and general relativity.
Despite the research team’s concerted efforts, substantial challenges persist, particularly given that the heavy isotopes synthesized during the r-process have never been successfully replicated on Earth.
Scientific understanding of their properties, including their atomic mass, decay half-life, and other characteristics, remains limited.
The theoretical framework involving high-energy jets, as proposed by the team, could potentially elucidate the origin of kilonovae – transient luminous events emitting optical and infrared electromagnetic radiation – which are associated with long-duration gamma-ray bursts.
“The disintegration of stars facilitated by high-energy photon jets presents an alternative genesis for the production of heavy elements and the potential kilonovae they might engender, a possibility previously unlinked to stellar collapse,” the scientists stated.
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Matthew R. Mumpower et al. 2025. Let There Be Neutrons! Hadronic Photoproduction from a Large Flux of High-energy Photons. ApJ 982, 81; doi: 10.3847/1538-4357/adb1e3
