Analytic heating rate of neutron star merger ejecta derived from Fermi's theory of beta decay

Kenta Hotokezaka, Re'em Sari, Tsvi Piran

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Macronovae (kilonovae) that arise in binary neutron star mergers are powered by radioactive beta decay of hundreds of r-process nuclides. We derive, using Fermi's theory of beta decay, an analytic estimate of the nuclear heating rate. We show that the heating rate evolves as a power law ranging between t-6/5 and t-4/3. The overall magnitude of the heating rate is determined by the mean values of nuclear quantities, e.g. the nuclear matrix elements of beta decay. These values are specified by using nuclear experimental data. We discuss the role of higher order beta transitions and the robustness of the power law. The robust and simple form of the heating rate suggests that observations of the late-time bolometric light curve α t-4/3 would be directevidence of a r-process driven macronova. Such observations could also enable us to estimate the total amount of r-process nuclei produced in the merger.

Original languageAmerican English
Pages (from-to)91-96
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 11 Jun 2017

Bibliographical note

Publisher Copyright:
© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


  • Gamma-ray burst: general
  • Stars: neutron


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