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Published July 2018 | Published + Accepted Version
Journal Article Open

The first direct double neutron star merger detection: Implications for cosmic nucleosynthesis

Abstract

Context. The astrophysical r-process site where about half of the elements, heavier than iron are produced, has been a puzzle for several decades. Here we discuss the role of one of the leading ideas – neutron star mergers (NSMs) – in the light of the first direct detection of such an event in both gravitational (GW) and electromagnetic (EM) waves. Aims. Our aim is to understand the implications of the first GW/EM observations of a NSM for cosmic nucleosynthesis. Methods. We analyse bolometric and NIR lightcurves of the first detected double NSM and compare them to nuclear reaction network-based macronova models. Results. The slope of the bolometric lightcurve is consistent with the radioactive decay of neutron star ejecta with Y_e ≲ 0.3 (but not larger), which provides strong evidence for an r-process origin of the electromagnetic emission. This rules out in particular "nickel winds" as major source of the emission. We find that the NIR lightcurves can be well fitted either with or without lanthanide-rich ejecta. Our limits on the ejecta mass together with estimated rates directly confirm earlier purely theoretical or indirect observational conclusions that double neutron star mergers are indeed a major site of cosmic nucleosynthesis. If the ejecta mass was typical, NSMs can easily produce all of the estimated Galactic r-process matter, and – depending on the real rate – potentially even more. This could be a hint that the event ejected a particularly large amount of mass, maybe due to a substantial difference between the component masses. This would be compatible with the mass limits obtained from the GW-observation. Conclusions. The recent observations suggests that NSMs are responsible for a broad range of r-process nuclei and that they are at least a major, but likely the dominant r-process site in the Universe.

Additional Information

© 2018 ESO. Article published by EDP Sciences. Received: 17 October 2017; Accepted: 4 April 2018; Published online 26 July 2018. We thank the anonymous referee for her/his insightful comments that helped to improve our paper. It is a great pleasure to thank Friedrich-Karl Thielemann for insightful discussions. SR has been supported by the Swedish Research Council (VR) under grant number 2016-03657_3, by the Swedish National Space Board under grant number Dnr. 107/16. SR, JS and AG are supported by the research environment grant "Gravitational Radiation and Electromagnetic Astrophysical Transients (GREAT)" funded by the Swedish Research council (VR) under Dnr 2016-06012. MMK acknowledges support by the GROWTH project funded by the National Science Foundation under PIRE Grant No 1545949. This work has further been supported by the CompStar network, COST Action MP1304. Some of the simulations were performed on the resources provided by the North-German Supercomputing Alliance (HLRN). A portion of this work was also carried out under the auspices of the National Nuclear Security Administration of the US Department of Energy at Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396 (O.K., R.W.). Some of the simulations used in this work were performed on the resources provided by the Los Alamos National Laboratory Institutional Computing Program (O.K.,R.W.). OK and RW are thankful to Aimee L. Hungerford, Chris L. Fryer, and Christopher J. Fontes for inspiring and productive discussions.

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Published - aa32117-17.pdf

Accepted Version - 1710.05445.pdf

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August 19, 2023
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