Urca cooling pairs in the neutron star ocean and their effect on superbursts
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
- The Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, East Lansing, MI 48824 (United States)
An accretion outburst onto a neutron star deposits hydrogen-rich and/or helium-rich material into the neutron star’s envelope. Thermonuclear burning of accreted material robustly produces Urca pairs—pairs of nuclei that undergo cycles of e{sup −}-capture and β{sup −}-decay. The strong T {sup 5} dependence of the Urca cooling neutrino luminosity means that Urca pairs in the neutron star interior potentially remove heat from accretion-driven nuclear reactions. In this study, we identify Urca pairs in the neutron star’s ocean—a plasma of ions and electrons overlaying the neutron star crust—and demonstrate that Urca cooling occurs at all depths in the ocean. We find that Urca pairs in the ocean and crust lower the ocean’s steady-state temperature during an accretion outburst and that unstable carbon ignition, which is thought to trigger superbursts, occurs deeper than it would otherwise. Cooling superburst light curves, however, are only marginally impacted by cooling from Urca pairs because the superburst peak radiative luminosity L{sub peak} is always much greater than the Urca pair neutrino luminosity L{sub ν} in the hot post-superburst ocean.
- OSTI ID:
- 22868555
- Journal Information:
- Astrophysical Journal, Vol. 831, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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