Gapless neutron superfluidity can explain the late time cooling of transiently accreting neutron stars

Abstract

The current interpretation of the observed late time cooling of transiently accreting neutron stars in low-mass X-ray binaries during quiescence requires the suppression of neutron superfluidity in their crust at variance with recent ab initio many-body calculations of dense matter. Focusing on the two emblematic sources KS~1731$-$260 and MXB~1659$-$29, we show that their thermal evolution can be naturally explained by considering the existence of a neutron superflow driven by the pinning of quantized vortices. Under such circumstances, we find that the neutron superfluid can be in a gapless state in which the specific heat is dramatically increased compared to that in the classical BCS state assumed so far, thus delaying the thermal relaxation of the crust. We have performed neutron-star cooling simulations taking into account gapless superfluidity and we have obtained excellent fits to the data thus reconciling astrophysical observations with microscopic theories. The imprint of gapless superfluidity on other observable phenomena is briefly discussed.

5 pages, 2 figures. Accepted for publication in Physical Review Letters

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Cited by in corpus (6)

• Dense Matter in Neutron Stars with eXTP
• Superfluid fraction in the crystalline crust of a neutron star: role of BCS pairing
• Cooling of neutron stars in soft X-ray transients with realistic crust composition
• Gapless neutron superfluidity in the crust of the accreting neutron stars KS 1731-260 and MXB 1659-29
• Detecting superfluid transition in the pulsar core
• Thermodynamic stability of superflows in General Relativity and Newtonian gravity