A nearby neutron-star merger explains the actinide abundances in the early Solar System

Abstract

A growing body of evidence indicates that binary neutron-star mergers are the primary origin of heavy elements produced exclusively through rapid neutron capture1,2,3,4 (the ‘r-process’). As neutron-star mergers occur infrequently, their deposition of radioactive isotopes into the pre-solar nebula could have been dominated by a few nearby events. Although short-lived r-process isotopes—with half-lives shorter than 100 million years—are no longer present in the Solar System, their abundances in the early Solar System are known because their daughter products were preserved in high-temperature condensates found in meteorites5. Here we report that abundances of short-lived r-process isotopes in the early Solar System point to their origin in neutron-star mergers, and indicate substantial deposition by a single nearby merger event. By comparing numerical simulations with the early Solar System abundance ratios of actinides produced exclusively through the r-process, we constrain the rate of occurrence of their Galactic production sites to within about 1−100 per million years. This is consistent with observational estimates of neutron-star merger rates6,7,8, but rules out supernovae and stellar sources. We further find that there was probably a single nearby merger that produced much of the curium and a substantial fraction of the plutonium present in the early Solar System. Such an event may have occurred about 300 parsecs away from the pre-solar nebula, approximately 80 million years before the formation of the Solar System.

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Fig. 1: The path of r-process elements.
Fig. 2: Simulated r-process abundance ratio near the pre-solar nebula.
Fig. 3: Simulated abundance ratios for multiple r-process isotopes.

Data availability

The datasets generated during and/or analysed during the current study are available in the Zenodo repository, https://doi.org/10.5281/zenodo.2556447. Source Data for Figs. 2 and 3 are provided with the paper.

Code availability

The computer code that was used for the calculations is available from the corresponding author upon reasonable request.

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Acknowledgements

We are grateful to S. Goldstein, D. Helfand, T. Huard, Z. Marka, P. Mueller, C. Scharf and W. Zajc for their valuable comments and suggestions. We also thank the University of Florida and Columbia University in the City of New York for their generous support.

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I.B. and S.M. contributed to the origination of the idea for the project and worked out the general details collaboratively. I.B. carried out the calculations.

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Correspondence to Imre Bartos.

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The authors declare no competing interests.

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Extended Data Table 1 Abundance ratios of r-process isotopes

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Bartos, I., Marka, S. A nearby neutron-star merger explains the actinide abundances in the early Solar System. Nature 569, 85–88 (2019). https://doi.org/10.1038/s41586-019-1113-7

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