Work

Cooling of Hybrid Stars with a 2SC+⟨ dd ⟩ Phase

Year: 2026

Type: article

Abstract: In 2019, Fujimoto, Fukushima, and Weise proposed a new color-superconductive state, the 2-flavor color superconducting (2SC)+$\mathinner {\langle {dd}\rangle }$ phase, which can be smoothly connected to the low-density baryon superfluidity in contrast to the 2SC phase. In this scenario, the neutron ${}^3P_2$ superfluidity on the low-density side of the phase transition is inherited by unpaired d-quarks in the 2SC phase on the high-density side. Since this could be realized in hybrid stars (neutron stars containing hadronic and quark matter), the 2SC+$\mathinner {\langle {dd}\rangle }$ phase may change the properties of neutron stars compared to the traditional 2SC phase. In this work, we study the thermal evolution of hybrid stars with the 2SC+$\mathinner {\langle {dd}\rangle }$ phase for the first time. We find that neutron stars with the 2SC+$\mathinner {\langle {dd}\rangle }$ phase become hotter than those with the 2SC phase, and are close to the color flavor-locked phase. The ${}^{3}P_2$ superfluidity plays an important role in cooling curves with not the 2SC but 2SC+$\mathinner {\langle {dd}\rangle }$ phases due to the suppression of quark $\beta$-decay. We therefore point out that, if the scenario of the 2SC+$\mathinner {\langle {dd}\rangle }$ phase is true, it could be specified through low-temperature observations such as those of Vela, 3C58, Vela Jr., and Vela-like pulsar.

Source: Progress of Theoretical and Experimental Physics

DOI: 10.1093/ptep/ptag122

Authors: Tsuneo Noda, Akira Dohi, Nobutoshi Yasutake, Huan Chen, Toshiki Maruyama, Toshitaka Tatsumi