Recent Advances in Understanding R-Process Nucleosynthesis in Metal-Poor Stars and Stellar Systems

Abstract

The rapid neutron-capture process (r-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 r-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. In this review, we explore r-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 r-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 r-process found in the oldest stars. Additionally, there are strong indications pointing towards additional sources of r-process-rich nuclei in the context of Galactic evolutionary timescales. 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 r-process nucleosynthesis in the coming years.

26 pages, 8 figures; Published in the journal Universe; This article belongs to the Special Issue "Advances in Nuclear Astrophysics"

References in corpus (64)

• Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
• Identification of strontium in the merger of two neutron stars
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• Neutron Star Mergers and Nucleosynthesis of Heavy Elements
• 4MOST: Project overview and information for the First Call for Proposals
• What is a globular cluster? An observational perspective
• AT2017gfo: an anisotropic and three-component kilonova counterpart of GW170817
• JWST detection of heavy neutron capture elements in a compact object merger
• Neutron-capture elements in the very metal-poor star HD122563
• Estimating the Contribution of Dynamical Ejecta in the Kilonova Associated with GW170817
• First stars VII. Lithium in extremely metal poor dwarfs
• Probing the Formation of the First Low-Mass Stars with Stellar Archaeology
• Production of Light Element Primary Process nuclei in neutrino-driven winds
• The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation
• Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars
• The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability
• Overview of the DESI Milky Way Survey
• The miniJPAS survey: a preview of the Universe in 56 colours
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• Neutron Star Mergers as the Origin of r-Process Elements in the Galactic Halo Based on the Sub-halo Clustering Scenario
• Multiple populations in globular clusters and their parent galaxies
• Revised and new proper motions for confirmed and candidate Milky Way dwarf galaxies
• The R-process Alliance: First Magellan/MIKE Release from the Southern Search for R-Process-enhanced Stars
• Remnants and ejecta of thermonuclear electron-capture supernovae: Constraining oxygen-neon deflagrations in high-density white dwarfs
• The Hamburg/ESO R-process Enhanced Star survey (HERES) X. HE 2252-4225, one more r-process enhanced and actinide-boost halo star
• High-resolution abundance analysis of very metal-poor r-I stars
• Lithium abundances in CEMP stars
• Magnetorotational supernovae: A nucleosynthetic analysis of sophisticated 3D models
• Enrichment history of r-process elements shaped by a merger of neutron star pairs
• Learning about the intermediate neutron-capture process from lead abundances
• Can neutron star mergers alone explain the r-process enrichment of the Milky Way?
• Beyond spectroscopy. I. Metallicities, distances, and age estimates for over twenty million stars from SMSS DR2 and Gaia EDR3
• The R-Process Alliance: Chemo-Dynamically Tagged Groups of Halo $r$-Process-Enhanced Stars Reveal a Shared Chemical-Evolution History
• Neutron-capture elements in the metal-poor globular cluster M15
• Horizons: Nuclear Astrophysics in the 2020s and Beyond
• Milky Way Tomography with the SkyMapper Southern Survey. II. Photometric Re-calibration of SMSS DR2
• Element abundance patterns in stars indicate fission of nuclei heavier than uranium
• The origins of light and heavy r-process elements identified by chemical tagging of metal-poor stars
• Signatures of R-process Enrichment in Supernovae from Collapsars
• J-PLUS: Stellar Parameters, C, N, Mg, Ca and [α/Fe] Abundances for Two Million Stars from DR1
• Detailed Abundances of 15 Stars in the Metal-Poor Globular Cluster NGC 4833
• Neutron rich matter in the laboratory and in the heavens after GW170817
• The R-Process Alliance: J1521-3538, a very metal-poor, extremely r-process-enhanced star with [Eu/Fe]=+2.2, and the class of r-III stars
• Stellar Loci V: Photometric Metallicities of 27 Million FGK Stars based on Gaia Early Data Release 3
• Correlations of r-Process Elements in Very Metal-Poor Stars as Clues to their Nucleosynthesis Sites
• The R-Process Alliance: Chemo-Dynamically Tagged Groups II. An Extended Sample of Halo $r$-Process-Enhanced Stars
• Hydrodynamic Simulations of Electron-capture Supernovae: Progenitor and Dimension Dependence
• Extreme r-process enhanced stars at high metallicity in Fornax
• The R-Process Alliance: Fifth Data Release from the Search for R-Process-Enhanced Metal-poor Stars in the Galactic Halo with the GTC
• Extremely metal-poor stars in the Fornax and Carina dwarf spheroidal galaxies
• r-process Abundance Patterns in the Globular Cluster M92
• The universality of the rapid neutron-capture process revealed by a possible disrupted dwarf galaxy star
• Chemical Evolution of R-process Elements in Stars (CERES): IV. An observational run-up of the third r-process peak with Hf, Os, Ir, and Pt
• Finding $r$-II sibling stars in the Milky Way with the Greedy Optimistic Clustering algorithm
• Actinide-boosting r Process in Black Hole-Neutron Star Merger Ejecta
• Proto-Neutron Star Convection and the Neutrino-Driven Wind: Implications for the r-Process
• Li distribution, kinematics and detailed abundance analysis among very metal-poor stars in the Galactic halo from the HESP-GOMPA survey
• Observations of multiple populations in star clusters
• The S-PLUS Ultra-Short Survey: first data release
• Discovery of an Extremely r-process-enhanced Thin-disk Star with [Eu/H] = +0.78
• Abundance Analysis of New $r$-Process-Enhanced Stars from the HESP-GOMPA Survey
• A chemodynamical analysis of bright metal-poor stars from the HESP-GOMPA survey -- Indications of a non-prevailing site for light r-process elements
• Internal r-process abundance spread of M15 and a single stellar population model
• Cosmological insights into the early accretion of r-process-enhanced stars II. Dynamical identification of lost members of Reticulum II