Direct Urca Processes with Hyperons in Cooling Neutron Stars

Abstract

In the relativistic mean field approximation, the relativistic energy losses of the direct Urca processes with nucleons (N-DURCA) and hyperons (Y-DURCA) are studied in the degenerate baryon matter of neutron stars. We investigate the effects of hyperon degrees of freedom and the Y-DURCA processes on the N-DURCA processes, and the total neutrino emissivity of neutron star matter. The results show that the existence of hyperons decreases the abundance of protons and leptons, and can sharply suppress the neutrino emissivity of the N-DURCA processes.

Gravitational Instability in Neutrino Dominated Accretion Disks

“…In our next work, we will take self-gravitation effects [9,13,14] into consideration for the vertical struc-ture of NDAFs, and calculate the variation of the vertical distribution of the density, temperature and electron fraction, and annihilation luminosity with different mass accretion rates and viscous parameters. In addition, we may discuss the mass of the possible fragments from the disk and its fall back timescale.…”

“…Gravitational instability has been studied in lots of astronomical phenomena. [9] It may cause the collapse of interstellar gas clouds and subsequent star formation. It is also discussed in the classical accretion disks.…”

“…( 8). The cooling due to the neutrino radiation 𝑄 𝜈 can be considered as the sum of Urca processes, [9] electron-positron pair annihilation, nucleon-nucleon bremsstrahlung, and plasmon decay (see Refs. [4,6]).…”

“…We numerically solve Eqs. (18) under the boundary condition (9) for 𝜌, 𝜐 𝑟 , 𝜐 𝜙 , 𝑐 𝑆 , 𝑃 , and 𝑇 by given 𝛼, Ṁ , 𝑀 , and 𝑟. In our calculations we take 𝑀 = 3𝑀 ⊙ .…”

Direct Urca processes involving singlet proton superfluidity in neutron star cooling

“…It means that all the possible baryon neutrino emission processes would happen during the neutrino cooling stage [11][12][13][14][15][16][17][18][19][20]. Among them, the most powerful enhancement of neutrino emission is provided by the nucleon direct Urca processes (NDUP), secondarily is the hyperon direct Urca processes (HDUP) [21][22][23][24][25][26][27][28]. Besides, the degrees of freedom of hyperons tend to soften the equation of state (EOS) calculated in the relativistic mean field (RMF) model based on SU (6) spin-flavor symmetry(quark model for the vector meson-hyperon coupling constants), then reduce the maximum mass of NS to about 1.6-1.7M ⊙ [29][30][31][32][33][34][35].…”