Kilonova r-Process Nucleosynthesis 2D: Reaction-Network…

What is Nucleosynthesis?

Nucleosynthesis is the process by which atomic nuclei are formed from protons and neutrons. In kilonova events, this process occurs as a result of neutron capture and beta decay in the aftermath of a neutron star merger.

This 2D model specifically focuses on the rapid neutron-capture process (r-process), where heavy elements are synthesized through a series of neutron captures followed by beta decays.

The r-Process and Neutron Capture

During kilonova events, the intense burst of neutrons from the merger of two neutron stars provides the necessary conditions for the r-process to occur. These neutrons are captured by seed nuclei, forming heavier elements.

Neutron capture is a key step in nucleosynthesis, where each successive capture increases the atomic mass number (A) while maintaining the proton-to-neutron ratio near stability.

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Beta Decay and Nucleus Stability

After neutron capture, the resulting nucleus may be unstable due to an imbalance in the proton-to-neutron ratio. To achieve stability, beta decay occurs, converting a neutron into a proton, an electron (beta particle), and an antineutrino.

This process continues until a stable isotope is formed, often at or near the magic numbers of nucleons (50, 82, 126) which correspond to full shells in the nucleus.

The Nuclide Chart and Nucleosynthesis Patterns

The nuclide chart is a graphical representation of all known isotopes. During nucleosynthesis, elements are formed at specific positions on this chart as they capture neutrons and undergo beta decay.

In the 2D model, you can observe how the abundance of different nuclei changes over time, forming distinct peaks corresponding to the stable isotopes that result from neutron captures and beta decays.

Frequently asked questions

What are kilonovae?

Kilonovae are the luminous events following a neutron star merger. They emit intense radiation, including light, as heavy elements are synthesized through the r-process.

Why is the r-process important for understanding heavy element formation?

The r-process explains how most of the heaviest elements in the universe, such as gold and platinum, are formed. It is crucial for our understanding of stellar nucleosynthesis and the chemical enrichment of galaxies.

How does this 2D model differ from a Monte-Carlo simulation?

This deterministic model directly integrates the flow equation across the full proton-number/mass-number grid, providing explicit numerical solutions. In contrast, Monte-Carlo simulations use stochastic sampling to approximate the nucleosynthesis process.

What are neutron shell closures and why do they matter?

Neutron shell closures occur at specific numbers of neutrons (50, 82, 126) that correspond to stable isotopes. These closures lead to the formation of distinct peaks in the abundance of heavy elements during nucleosynthesis.

Try it live

Everything above runs in your browser — open Kilonova r-process Nucleosynthesis 2D: Reaction-Network Flow and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Kilonova r-process Nucleosynthesis 2D: Reaction-Network Flow simulation

Kilonova r-Process Nucleosynthesis 2D: Reaction-Network Flow