Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | A301 | |
Number of page(s) | 14 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361/202348340 | |
Published online | 18 October 2024 |
Layers of electron captures in the crust of accreting neutron stars
1
Nicholas and Lee Begovich Center for Gravitational Wave Physics and Astronomy, California State University Fullerton, Fullerton, California 92831, USA
2
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, PL-00-716 Warszawa, Poland
3
Laboratoire Univers et Théories, Observatoire de Paris, Université PSL, Université Paris Cité, CNRS, F-92190 Meudon, France
Received:
20
October
2023
Accepted:
9
August
2024
The accumulation of accreted matter onto the neutron star surface triggers exothermic reactions in the crust. The heat released as a result influences the luminosity exhibited by the X-ray transient. The most common approach to the kinetics of exothermic reactions in the crust of accreting neutron stars is to consider an infinite reaction rate. Here, we investigate accretion-related heat release in the accreted outer crust of a neutron star by including a time-dependent accretion cycle and experimentally based reaction rates in the kinetics of electron captures above the reaction threshold. A simple model was used to compute the zero temperature equation of state of a crust in which two nuclei can coexist. We solved the abundance of parent nuclei as a function of the depth in the star and the time variable using astrophysically motivated features of the accreting system. We calculated the heat release and neutrino loss associated to reactions in the outer crust. We report the existence of layers in the outer crust, which contain both parent and grand-daughter nuclei of electron captures. The reactions can occur deeper in the shell than the reaction threshold, thus releasing more heat per accreted baryon for a given accretion rate. The electron capture layers continue to exist even when the accretion has stopped. The heat sources are time- and pressure-dependent in accreting crusts of neutron stars. The total heat released is a function of astrophysical (active and quiescent time) and microscopic (reaction rate) parameters Therefore, we conclude these parameters should be considered individually and carefully for a range of different sources.
Key words: accretion / accretion disks / dense matter / equation of state / nuclear reactions / nucleosynthesis / abundances / stars: neutron
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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