Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems
The rapid neutron-capture process (<i>r</i>-process) is responsible for the creation of roughly half of the elements heavier than iron, including precious metals like silver, gold, and platinum, as well as radioactive elements such as thorium and uranium. Despite its importance, the natu...
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| author | Avrajit Bandyopadhyay Timothy C. Beers |
| author_facet | Avrajit Bandyopadhyay Timothy C. Beers |
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| description | The rapid neutron-capture process (<i>r</i>-process) is responsible for the creation of roughly half of the elements heavier than iron, including precious metals like silver, gold, and platinum, as well as radioactive elements such as thorium and uranium. Despite its importance, the nature of the astrophysical sites where the <i>r</i>-process occurs, and the detailed mechanisms of its formation, remain elusive. The key to resolving these mysteries lies in the study of chemical signatures preserved in ancient, metal-poor stars. These stars, which formed in the early Universe, retain the chemical fingerprints of early nucleosynthetic events and offer a unique opportunity to trace the origins of <i>r</i>-process elements in the early Galaxy. In this review, we explore the state-of-the-art understanding of <i>r</i>-process nucleosynthesis, focusing on the sites, progenitors, and formation mechanisms. We discuss the role of potential astrophysical sites such as neutron star mergers, core-collapse supernovae, magneto-rotational supernovae, and collapsars, that can play a key role in producing the heavy elements. We also highlight the importance of studying these signatures through high-resolution spectroscopic surveys, stellar archaeology, and multi-messenger astronomy. Recent advancements, such as the gravitational wave event GW170817 and detection of the <i>r</i>-process in the ejecta of its associated kilonovae, have established neutron star mergers as one of the confirmed sites. However, questions remain regarding whether they are the only sites that could have contributed in early epochs or if additional sources are needed to explain the signatures of <i>r</i>-process found in the oldest stars. Additionally, there are strong indications pointing towards additional sources of <i>r</i>-process-rich nuclei in the context of Galactic evolutionary timescales. These are several of the outstanding questions that led to the formation of collaborative efforts such as the <i>R</i>-Process Alliance, which aims to consolidate observational data, modeling techniques, and theoretical frameworks to derive better constraints on deciphering the astrophysical sites and timescales of <i>r</i>-process enrichment in the Galaxy. This review summarizes what has been learned so far, the challenges that remain, and the exciting prospects for future discoveries. The increasing synergy between observational facilities, computational models, and large-scale surveys is poised to transform our understanding of <i>r</i>-process nucleosynthesis in the coming years. |
| format | Article |
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| institution | Kabale University |
| issn | 2218-1997 |
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| publishDate | 2025-07-01 |
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| spelling | doaj-art-b02ff9e0028049b9bdec4d3f75dc52682025-08-20T03:32:16ZengMDPI AGUniverse2218-19972025-07-0111722910.3390/universe11070229Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar SystemsAvrajit Bandyopadhyay0Timothy C. Beers1Department of Astronomy, University of Florida, Gainesville, FL 32611, USADepartment of Physics and Astronomy, University of Notre Dame, Notre Dame, IN 46556, USAThe rapid neutron-capture process (<i>r</i>-process) is responsible for the creation of roughly half of the elements heavier than iron, including precious metals like silver, gold, and platinum, as well as radioactive elements such as thorium and uranium. Despite its importance, the nature of the astrophysical sites where the <i>r</i>-process occurs, and the detailed mechanisms of its formation, remain elusive. The key to resolving these mysteries lies in the study of chemical signatures preserved in ancient, metal-poor stars. These stars, which formed in the early Universe, retain the chemical fingerprints of early nucleosynthetic events and offer a unique opportunity to trace the origins of <i>r</i>-process elements in the early Galaxy. In this review, we explore the state-of-the-art understanding of <i>r</i>-process nucleosynthesis, focusing on the sites, progenitors, and formation mechanisms. We discuss the role of potential astrophysical sites such as neutron star mergers, core-collapse supernovae, magneto-rotational supernovae, and collapsars, that can play a key role in producing the heavy elements. We also highlight the importance of studying these signatures through high-resolution spectroscopic surveys, stellar archaeology, and multi-messenger astronomy. Recent advancements, such as the gravitational wave event GW170817 and detection of the <i>r</i>-process in the ejecta of its associated kilonovae, have established neutron star mergers as one of the confirmed sites. However, questions remain regarding whether they are the only sites that could have contributed in early epochs or if additional sources are needed to explain the signatures of <i>r</i>-process found in the oldest stars. Additionally, there are strong indications pointing towards additional sources of <i>r</i>-process-rich nuclei in the context of Galactic evolutionary timescales. These are several of the outstanding questions that led to the formation of collaborative efforts such as the <i>R</i>-Process Alliance, which aims to consolidate observational data, modeling techniques, and theoretical frameworks to derive better constraints on deciphering the astrophysical sites and timescales of <i>r</i>-process enrichment in the Galaxy. This review summarizes what has been learned so far, the challenges that remain, and the exciting prospects for future discoveries. The increasing synergy between observational facilities, computational models, and large-scale surveys is poised to transform our understanding of <i>r</i>-process nucleosynthesis in the coming years.https://www.mdpi.com/2218-1997/11/7/229nucleosynthesisr-processneutron capture processesmetal-poor starschemical abundancesglobular clusters |
| spellingShingle | Avrajit Bandyopadhyay Timothy C. Beers Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems Universe nucleosynthesis r-process neutron capture processes metal-poor stars chemical abundances globular clusters |
| title | Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems |
| title_full | Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems |
| title_fullStr | Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems |
| title_full_unstemmed | Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems |
| title_short | Recent Advances in Understanding <i>R</i>-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems |
| title_sort | recent advances in understanding i r i process nucleosynthesis in metal poor stars and stellar systems |
| topic | nucleosynthesis r-process neutron capture processes metal-poor stars chemical abundances globular clusters |
| url | https://www.mdpi.com/2218-1997/11/7/229 |
| work_keys_str_mv | AT avrajitbandyopadhyay recentadvancesinunderstandingiriprocessnucleosynthesisinmetalpoorstarsandstellarsystems AT timothycbeers recentadvancesinunderstandingiriprocessnucleosynthesisinmetalpoorstarsandstellarsystems |