Fizicienii sugerează că stelele în ultimele lor momente s-ar desfășura și ar crea astfel elemente grele.

Understanding the origin of heavy elements in the periodic table is one of the most challenging problems in physics. A team from the Los Alamos National Laboratory in the U.S. is exploring an uncharted territory: the gamma-ray jets and the surrounding cocoon emerging from collapsed stars. This research, presented in The Astrophysical Journal, suggests that high-energy photons produced deep within these jets could dissolve the outer layers of a star into neutrons, initiating a series of physical processes that lead to the formation of heavy elements.

Matthew Mumpower, a physicist at Los Alamos, explains that creating heavy elements like uranium and plutonium requires extreme conditions. Few cosmic scenarios allow for their formation, all necessitating an abundance of neutrons. The proposed phenomenon involves dynamically generating these neutrons rather than having an initial supply.

Neutrons have a short half-life of about 15 minutes, limiting scenarios for their availability in quantities sufficient for heavy element formation. The key to producing the heaviest elements lies in the rapid neutron capture process, known as the "r-process," believed to be responsible for most of the naturally occurring thorium, uranium, and plutonium in the universe.

The framework the team proposes aims to understand the challenging physics behind the r-process by outlining reactions and processes occurring around stellar collapse that could lead to heavy element formation. This framework also addresses critical questions related to neutron transport, multiphysics simulations, and the observation of rare events—all of which bear implications for national security applications derived from this research.

In Mumpower’s proposed scenario, a massive star approaches the end of its life as its nuclear fuel runs out. With no energy left to counteract its own gravity, a black hole forms at the star’s center. If this black hole rotates rapidly enough, its strong gravitational effects twist the surrounding spacetime and launch a powerful jet. Through successive reactions, a broad spectrum of photons is created, some with extremely high energies.

This jet penetrates the star, creating a hot cocoon of material around it. At the interface of the jet and the stellar material, high-energy photons can interact with atomic nuclei, transmuting protons into neutrons. Existing atomic nuclei can also be dissolved into individual nucleons, generating even more free neutrons to fuel the r-process. The team’s calculations indicate that the interaction between light and matter can create neutrons extraordinarily quickly, on the order of nanoseconds.

Due to their charge, protons are trapped within the jet by strong magnetic fields. Neutrons, being neutral, are expelled into the cocoon. After experiencing a relativistic shock, these neutrons become extremely dense compared to the surrounding stellar material, allowing the r-process to commence, forging heavy elements and isotopes that are expelled into space as the star disintegrates.

This process of converting protons into neutrons and allowing free neutrons to escape into the surrounding cocoon to form heavy elements involves various physical principles and incorporates all four fundamental forces of nature. Nevertheless, challenges persist, as the heavy isotopes created during the r-process have never been made on Earth, and researchers know little about their properties, such as atomic mass and half-life.

The theoretical framework proposed by the team for high-energy jets could also help explain the origin of kilonovae—brilliant bursts of electromagnetic radiation in the optical and infrared spectra associated with long gamma-ray bursts. Until now, kilonovae have primarily been linked to the collision of two neutron stars or the merger of a neutron star with a black hole. These intense collisions might serve to confirm through observations the "cosmic factories" of heavy elements.

The dissolution of stars via high-energy photon jets presents an alternative origin for the production of heavy elements and associated kilonovae—a possibility not previously associated with collapsing stars. Scientists have also discovered iron and plutonium in sediment from the ocean floor. These deposits have been confirmed as extraterrestrial in origin, although, similar to events producing kilonovae, the exact cosmic sources remain unknown. The proposed scenario involving high-energy jets from collapsed stars offers an intriguing possibility for the sources of these heavy elements found beneath the sea.

To fully understand their proposed framework, Mumpower and his team plan to run simulations of their models, including complex microphysics interactions. This research not only contributes to the fundamental understanding of heavy element formation but also holds implications for various fields, including astrophysics and national security. As scientists continue to explore these cosmic phenomena, they hope to unravel the intricate connections between stellar events and the elemental makeup of our universe.