Fusion of neutron rich oxygen isotopes in the crust of accreting neutron stars

Abstract

Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge $Z$. Nuclei with $Z\le 6$ can fuse at low densities in a liquid ocean. However, nuclei with Z=8 or 10 may not burn until higher densities where the crust is solid and electron capture has made the nuclei neutron rich. We calculate the $S$ factor for fusion reactions of neutron rich nuclei including ${}^{24}$O + ${}^{24}$O and ${}^{28}$Ne + ${}^{28}$Ne. We use a simple barrier penetration model. The $S$ factor could be further enhanced by dynamical effects involving the neutron rich skin. This possible enhancement in $S$ should be studied in the laboratory with neutron rich radioactive beams. We model the structure of the crust with molecular dynamics simulations. We find that the crust of accreting neutron stars may contain micro-crystals or regions of phase separation. Nevertheless, the screening factors that we determine for the enhancement of the rate of thermonuclear reactions are insensitive to these features. Finally, we calculate the rate of thermonuclear ${}^{24}$O + ${}^{24}$O fusion and find that ${}^{24}$O should burn at densities near $10^{11}$ g/cm${}^3$. The energy released from this and similar reactions may be important for the temperature profile of the star.

7 pages, 4 figs, minor changes, to be published in Phys. Rev. C

References in corpus (5)

• Models of crustal heating in accreting neutron stars
• Coulomb tunneling for fusion reactions in dense matter: Path integral Monte Carlo versus mean field
• Fusion reactions in multicomponent dense matter
• Cooling of the quasi-persistent neutron star X-ray transients KS 1731-260 and MXB 1659-29
• Phase separation in the crust of accreting neutron stars

Cited by in corpus (17)

• Possible Resonances in the 12C + 12C Fusion Rate and Superburst Ignition
• Cooling of the crust in the neutron star low-mass X-ray binary MXB 1659-29
• Microscopic sub-barrier fusion calculations for the neutron star crust
• The Variable Quiescent X-ray Emission of the Neutron Star Transient XTE J1701-462
• Rapid Cooling of the Neutron Star in the Quiescent Super-Eddington Transient XTE J1701-462
• Neon Cluster Formation and Phase Separation During White Dwarf Cooling
• Thermal conductivity and phase separation of the crust of accreting neutron stars
• The structure of accreted neutron star crust
• Sub-barrier enhancement of fusion as compared to a microscopic method in 18O+12C
• Nuclear and dark matter heating in massive white dwarf stars
• Experimental constraints on shallow heating in accreting neutron-star crusts
• The Swift capture of a long X-ray burst from XTE J1701-407
• Enhanced dynamics in fusion of neutron-rich oxygen nuclei at above-barrier energies
• Nuclear Quantum Many-Body Dynamics: From Collective Vibrations to Heavy-Ion Collisions (2nd edition)
• Heating in Magnetar Crusts from Electron Captures
• Impact of Pycnonuclear Fusion Uncertainties on the Cooling of Accreting Neutron Star Crusts
• Crust composition and the Shallow Heat Source in KS 1731-260