Can Neutron Star Mergers Alone Explain the r-process Enrichment of the Milky Way?

Mandel, Ilya; Belczyński, Krzysztof; Goriely, Stéphane; Janka, Hans-Thomas; Just, Oliver; Ruiter, Ashley J.; Vanbeveren, D.; Kruckow, Matthias U.; Briel, M. M.; Eldridge, J. J.; Stanway, Elizabeth R.

doi:10.3847/2041-8213/acad82

Cited by 31 publications

(12 citation statements)

References 126 publications

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“…The multimessenger detection of the neutron star merger (NSM) GW170817 (Abbott et al 2017) confirmed (Drout et al 2017;Kasen et al 2017;Kasliwal et al 2017;Tanaka et al 2017;Watson et al 2019) the long-standing theory that the decompression of NS material following its disruption during a merger could trigger an r-process (Lattimer & Schramm 1974, 1976Symbalisty & Schramm 1982;Meyer 1989;Davies et al 1994;Freiburghaus et al 1999). However, questions remain as to whether NSMs can explain the full pattern of r-process enrichment observed across time and space (e.g., Côté et al 2019;Zevin et al 2019;van de Voort et al 2020;Jeon et al 2021;Molero et al 2021;de los Reyes et al 2022;Naidu et al 2022;Cavallo et al 2023;Kobayashi et al 2023).…”

Section: Introductionmentioning

confidence: 80%

Hydrodynamic Mixing of Accretion Disk Outflows in Collapsars: Implications for r-process Signatures

Barnes

Duffell

2023

ApJ

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The astrophysical environments capable of triggering heavy-element synthesis via rapid neutron capture (the r-process) remain uncertain. While binary neutron star mergers (NSMs) are known to forge r-process elements, certain rare supernovae (SNe) have been theorized to supplement—or even dominate—r-production by NSMs. However, the most direct evidence for such SNe, unusual reddening of the emission caused by the high opacities of r-process elements, has not been observed. Recent work identified the distribution of r-process material within the SN ejecta as a key predictor of the ease with which signals associated with r-process enrichment could be discerned. Though this distribution results from hydrodynamic processes at play during the SN explosion, thus far it has been treated only in a parameterized way. We use hydrodynamic simulations to model how disk winds—the alleged locus of r-production in rare SNe—mix with initially r-process-free ejecta. We study mixing as a function of the wind mass, wind duration, and the initial SN explosion energy, and find that it increases with the first two of these and decreases with the third. This suggests that SNe accompanying the longest long-duration gamma-ray bursts are promising places to search for signs of r-process enrichment. We use semianalytic radiation transport to connect hydrodynamics to electromagnetic observables, allowing us to assess the mixing level at which the presence of r-process material can be diagnosed from SN light curves. Analytic arguments constructed atop this foundation imply that a wind-driven r-process-enriched SN model is unlikely to explain standard energetic SNe.

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Section: Introductionmentioning

confidence: 80%

Hydrodynamic Mixing of Accretion Disk Outflows in Collapsars: Implications for r-process Signatures

Barnes

Duffell

2023

ApJ

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“…Since the gravitational wave detection from the neutron star merger GW170817 (Abbott et al 2017) and subsequent spectroscopic observations (Watson et al 2019), neutron star mergers are probably the main producers of rprocess elements, as predicted by modern simulations (Thielemann et al 2017). Recently, Ekanger et al 2023 confirmed that black hole-neutron star mergers also produce a significant amount of r-process elements through nucleosynthesis yields from numerical simulations, as indicated by previous studies as well (e.g., Lattimer & Schramm 1976;Freiburghaus et al 1999;Nishimura et al 2016;Kobayashi et al 2023). The r-process also happens at other astrophysical sites, such as core-collapse supernovae (e.g., Wheeler et al 1998;Ekanger et al 2023) and magnetorotational supernovae (e.g., Winteler et al 2012;Reichert et al 2021Reichert et al , 2023.…”

Section: Introductionmentioning

confidence: 54%

A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE

Sales-Silva,

Cunha,

Smith

et al. 2024

ApJ

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This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of ∼2000 stars in the Galactic bulge bar spatially contained within ∣X Gal∣ < 5 kpc, ∣Y Gal∣ < 3.5 kpc, and ∣Z Gal∣ < 1 kpc, and spanning metallicities between −2.0 ≲ [Fe/H] ≲ +0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our bulge-bar sample when compared to Nd, with the r-process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd] < 0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r-process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the bulge dominated by yields from core-collapse supernovae and r-process astrophysical sites, such as magnetorotational supernovae.

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“…Some studies suggest that these merger rates depend on redshift and metallicity such that in low metallicity environments, the BHNS merger rate is actually higher than the BNS merger rate. This would alter the evolution history of enrichment of stars with heavy nuclei, and also in principle change the distribution of BH masses and spins (see Kobayashi et al 2023, and sources therein). To check the robustness of the local rate assumption, we look at the redshift evolution of BHNS mergers within a redshift of ∼ 0.05 (corresponding to the proposed LIGO O4 BNS sensitivity range and LSST's magnitude limited distance of ∼ 200 Mpc) for the three models in Zhu et al (2021b).…”

Section: Discussionmentioning

confidence: 99%

“…In parallel, another method used to understand this question involves considering the abundance evolution over time for all elements, known as galactic chemical evolution (GCE; see, e.g., Côté et al 2017Côté et al , 2018Kobayashi et al 2020). GCE studies combine galaxy evolution, population syntheses of transients like mergers and supernovae, and nucleosynthesis models to explain the sources of the periodic table (Côté et al 2019;Kobayashi et al 2023). Considering a holistic view of the sources of all the elements, that can fold in nucleosynthesis results, is an important, and independent, theoretical approach for understanding the sources of the r-process elements.…”

Section: Introductionmentioning

confidence: 99%

Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae

Nick¹,

Bhattacharya²,

Horiuchi³

2023

Preprint

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We perform a comparative analysis of nucleosynthesis yields from binary neutron star (BNS) mergers, black hole-neutron star (BHNS) mergers, and core-collapse supernovae (CCSNe) with the goal of determining which are the most dominant sources of rprocess enrichment observed in stars. We find that BNS and BHNS binaries may eject similar mass distributions of robust r-process nuclei post merger (up to 3rd peak and actinides, A ∼ 200 − 240), after accounting for the volumetric event rates. Magnetorotational (MR) CCSNe likely undergo a weak r-process (up to A ∼ 140) and contribute to the production of light element primary process (LEPP) nuclei, whereas typical thermal, neutrino-driven CCSNe only synthesize up to 1st r-process peak nuclei (A ∼ 80 − 90). We also find that the upper limit to the rate of MR CCSNe is 1% the rate of typical thermal CCSNe; if the rate was higher, then weak r-process nuclei would be overproduced. Although the largest uncertainty is from the volumetric event rate, the prospects are encouraging for confirming these rates in the next few years with upcoming surveys. Using a simple model to estimate the resulting kilonova light curve from mergers and our set of fiducial merger parameters, we predict that ∼ 7 BNS and ∼ 2 BHNS events will be detectable per year by the Vera C. Rubin Observatory (LSST), with prior gravitational wave (GW) triggers.

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Can Neutron Star Mergers Alone Explain the r-process Enrichment of the Milky Way?

Cited by 31 publications

References 126 publications

Hydrodynamic Mixing of Accretion Disk Outflows in Collapsars: Implications for r-process Signatures

Hydrodynamic Mixing of Accretion Disk Outflows in Collapsars: Implications for r-process Signatures

A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE

Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae

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