# Neutron Star Mergers and their Impact on Second Generation Star Formation in the Early Universe

**Authors:** Danielle Skinner, John H. Wise  
**arXiv:** [2307.10354](https://arxiv.org/abs/2307.10354)  
**Date:** 2023-07-19  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.10354v1/

## Key points

- The study of the evolution of elements in the universe is still being investigated
- Supernova explosions play a crucial role in enriching the universe with new metals
- Neutron stars can form as remnants of supernovae and have unique properties worth studying
- Neutron star mergers can give rise to the r-process, which produces heavy elements through rapid neutron capture reactions
- Researchers conducted simulations to understand how neutron star mergers enrich their surroundings and affect second-generation stars' metal abundances
- Higher explosion energy leads to more highly enhanced r-process stars, while lower explosion energy results in a higher mass fraction of stars enhanced by r-process elements but not highly enhanced
- Shorter delay times between neutron star merger events lead to a higher mass fraction of stars being enhanced by r-process elements, but fewer highly enhanced stars compared to longer delay times
- This study provides valuable insights into enrichment processes and metal abundances in subsequent generations of stars

## Summary

The study of the evolution of elements in the universe, from the simplest ones like hydrogen and helium to heavier elements such as gold and platinum, is still a subject of intense investigation. One important process in this evolution is the enrichment of the universe with new metals through supernova explosions. These explosions occur when the very first stars in the universe reach the end of their lives and release their enriched material into their surroundings. As a result, neutron stars can form as remnants of these supernovae. Neutron stars have unique properties that make them interesting objects to study. They can end up in binary systems with other neutron stars, and if these systems merge, they can give rise to a phenomenon known as the r-process. The r-process is responsible for the production of heavy elements through rapid neutron capture reactions. In this work, researchers focused on understanding how a single neutron star merger (NSM) can enrich its surrounding environment early in its evolution and how this enrichment affects the formation of second-generation stars and their metal abundances. To investigate this scenario, they conducted high-resolution cosmological zoom-in simulations using a computational tool called Enzo. The researchers implemented a new NSM model in their simulations, varying both the explosion energy and delay time. They found that NSMs have a significant impact on enriching second-generation stars with r-process elements. When the explosion energy is high, almost all enhanced r-process stars show high levels of enhancement. On the other hand, when the explosion energy is lower, there is a higher mass fraction of stars that are enhanced by r-process elements but not as many are highly enhanced. Additionally, they observed that shorter delay times between NSM events result in a higher mass fraction of stars being enhanced by r-process elements compared to longer delay times; however shorter delay times also lead to a smaller mass fraction of highly enhanced stars compared to longer delay times. Overall, this study provides valuable insights into how neutron star mergers affect enrichment processes within their surrounding environments and influence subsequent generations' metal abundances. It represents an important step towards better understanding complex processes involved in element evolution throughout our cosmos and contributes to ongoing efforts to unravel mysteries regarding heavy element origins and distributions across space.