R-process Rain from Binary Neutron Star Mergers in the Galactic Halo

Abstract

Compact binary mergers involving at least one neutron star are promising sites for the synthesis of $\text{r}$-process elements found in stars and planets. However, mergers can take place at significant offsets from their host galaxies, with many occurring several kpc from star-forming regions. It is thus important to understand the physical mechanisms involved in transporting enriched material from merger sites in the galactic halo to the star-forming disk. We investigate these processes, starting from an explosive injection event and its interaction with the halo medium. We show that the total outflow mass in compact binary mergers is too low for the material to travel to the disk in a ballistic fashion. Instead, the enriched ejecta is swept into a shell, which decelerates over $\lesssim 10$ pc scales and becomes corrugated by the Rayleigh-Taylor instability. The corrugated shell is denser than the ambient medium, and breaks into clouds which sink toward the disk. These sinking clouds lose thermal energy through radiative cooling, and are also ablated by shearing instabilities. We present a dynamical heuristic that models these effects to predict the delay times for delivery to the disk. However, we find that turbulent mass ablation is extremely efficient, and leads to the total fragmentation of sinking $\text{r}$-process clouds over $10-100$ pc scales. We thus predict that enriched material from halo injection events quickly assimilates into the gas medium of the halo, and that enriched mass flow to the disk could only be accomplished through turbulent diffusion or large-scale inflowing mass currents.

arXiv comment12 pages, 5 figures

References in corpus (48)

• Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
• How Do Galaxies Get Their Gas?
• Galactic Winds
• Interstellar Turbulence I: Observations and Processes
• Short-Duration Gamma-Ray Bursts
• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis
• Nucleosynthesis in neutrino-driven winds: I. The physical conditions
• Mapping Large-Scale Gaseous Outflows in Ultraluminous Galaxies with Keck II ESI Spectra: Variations in Outflow Velocity with Galactic Mass
• The Observed Offset Distribution of Gamma-Ray Bursts from Their Host Galaxies: A Robust Clue to the Nature of the Progenitors
• Production of all the r-process nuclides in the dynamical ejecta of neutron star mergers
• On the astrophysical robustness of neutron star merger r-process
• The mass ejection from the merger of binary neutron stars
• R-Process Nucleosynthesis in Dynamically Ejected Matter of Neutron Star Mergers
• Gaseous Galaxy Halos
• R-process enrichment from a single event in an ancient dwarf galaxy
• Collapsars as a major source of r-process elements
• The r-process nucleosynthesis in the various jet-like explosions of magnetorotational core-collapse supernovae
• The Locations of Short Gamma-ray Bursts as Evidence for Compact Object Binary Progenitors
• On the formation history of Galactic double neutron stars
• The long-term evolution of neutron star merger remnants - I. The impact of r-process nucleosynthesis
• Estimating the Contribution of Dynamical Ejecta in the Kilonova Associated with GW170817
• Hubble Space Telescope Observations of Short GRB Host Galaxies: Morphologies, Offsets, and Local Environments
• The Origin of r-Process Elements in the Milky Way
• The cocoon emission - an electromagnetic counterpart to gravitational waves from neutron star mergers
• r-Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole - Neutron Star Mergers
• The survival of gas clouds in the Circumgalactic Medium of Milky Way-like galaxies
• Short-lived ${}^{244}$Pu Points to Compact Binary Mergers as Sites for Heavy r-process Nucleosynthesis
• Numerical simulations of the jet dynamics and synchrotron radiation of binary neutron star merger event GW170817/GRB170817A
• On the Progenitor of Binary Neutron Star Merger GW170817
• Rayleigh-Taylor instability in Magnetohydrodynamic Simulations of the Crab Nebula
• Gas Condensation in the Galactic Halo
• High Velocity Rain: The Terminal Velocity of Model of Galactic Infall
• R-Process elements from magnetorotational hypernovae
• Simulations of High-Velocity Clouds. I. Hydrodynamics and High-Velocity High Ions
• Evidence from Disrupted Halo Dwarfs that $r$-process Enrichment via Neutron Star Mergers is Delayed by $\gtrsim 500$ Myrs
• The lanthanide fraction distribution in metal-poor stars: a test of neutron star mergers as the dominant r-process site
• r-process enrichment of ultra-faint dwarf galaxies by fast merging double neutron stars
• The delayed time distribution of massive double compact star mergers
• Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
• Dust formation in macronovae
• No velocity-kicks are required to explain large-distance offsets of Ca-rich supernovae and short-GRBs
• Turbulent mixing of r-process elements in the Milky Way
• Merger delay time distribution of extended emission short GRBs
• Evidence for r-process delay in very metal-poor stars
• Mass, Morphing, Metallicities: The Evolution of Infalling High Velocity Clouds
• The Location and Environments of Neutron Star Mergers in an Evolving Universe
• Modelling the chemical evolution of the Milky Way

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