and a massive core (e.g., Ref. [@nsb1]). The crust constitutes a few per cent of the star’s mass and is about $\sim 1$ km thick. The mass density $\rho$ at the crust-core boundary is $\approx \rho_0/2$, where $\rho_0\approx 2.8 \times 10^{14}$ g cm$^{-3}$ is the density of saturated nuclear matter. The crust is further divided into the outer and inner crust. The outer crust (more generally, the outer envelope; where $\rho$ is below the neutron drip density $\la 4 \times 10^{11}$ g cm$^{-3}$) consists of atomic nuclei and strongly degenerate electrons. In the inner crust, free neutrons appear in addition to the electrons and nuclei; these neutrons can be in superfluid state.

  Process                                                                    $Q_{\rm s}$ \[erg cm$^{-3}$ s$^{-1}$\]
  ---------------- --------------------------------------------------------- ----------------------------------------
  Modified Urca    ${\rm n+N\to p+N+e+}\bar{\nu}$ ${\rm p+N+e\to n+N+}\nu$   $ 10^{20}-3 \times 10^{21}$
  Bremsstrahlung   ${\rm N+N\to N+N+}\nu+\bar{\nu}$                          $ 10^{19}-10^{20}_{}$

  : Main slow neutrino emission in nucleon matter

\[tab-nucore-slow\]

The neutron star core can be divided into the outer and inner core. The outer core extends to $\rho \sim (2-3) \rho_0$ and consists of neutrons (n), with an admixture of protons (p), electrons (e) and possibly muons. All these particles are strongly degenerate. The inner core extends to the stellar center 