Nucleosynthesis in decompressed Neutron stars crust matter Sarmistha Banik Collaborators: Smruti Smita Lenka & B. Hareesh Gautham BITS-PILANI, Hyderabad Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Content Introduction Decompressed matter at Nuclear Statistical Equilibrium (NSE) Result Summary Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Introduction Understanding the formation of heavy and super heavy nuclei in the universe is a challenging problem. Element upto Fe is produced through fusion in star interior. Elements heavier than Fe are produced by neutron capture. The rapid neutron capture process (r-process) has long been known to be responsible for the production of many heavy, neutron-rich nuclei. Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Decompressed Matter One of the possible sites of r process is NS-NS mergers or NS-BH mergers. During the last phases of their inspiral process long tidal arms develop stretching into a disc/torus made of cold material from their crust. Through its expansion, this material decompresses, which may be accompanied by r- process. [ J. M. Lattimer & D.N. Schramm, APJ 213 (1977) 225. ] End products of r-process depend on the initial composition of the matter before decompression. Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Neutron star structure Atmosphere (atoms) n ≤ 10 4 g/cm 3 Outer Crust (free e − s, lattice of nuclei) 10 4 −4×10 11 g/cm 3 Inner crust (lattice of nuclei with free e − s and neutrons) Outer core (atomic particle fluid) Inner core (exotic subatomic particles) n ≥ g/cm 3 Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Importance of crust Crust thermal conductivity is important to determine the relation between observed X-ray flux and the temperature of the core. Electrical resistivity of the crust is important for the evolution of NS magnetic field. The presence of crystal lattice of atomic nuclei is mandatory for modelling of radio-pulsar glitches. Can make rapidly rotating pulsar a source of gravitational waves. Instabilities in the fusion of light elements in the outer crust of an accreting NS, are thought to be responsible for X-ray bursts. Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Magnetic field in Neutron stars Intense magnetic field is (B ∼ G) believed to exist on the surfaces of some neutron stars. For magneters B is upto G. Inside the star the magnitude of fields may be even higher. The limiting interior field strength for a star is set by the virial theorem, 2T + W + 3Π +M = 0 T = total rotational kinetic energy W = gravitational potential energy Π = due to internal energy M = magnetic energy. Since T, Π > 0, M max ∼ W. Such high magnetic fields motivate the study of the physical properties of the Neutron Star matter in fields of extreme magnitude. Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

NS crust in the presence of B The composition of the Neutron Star inner crust as a function of density in presence of strong magnetic fields was determined by R. Nandi et. al. [Astrophys. J 736 (2011) 156] Inner crust of a Neutron Star begins at neutron drip point defined by µ n = m n c 2. It contains nuclear cluster immersed in electron and neutron gas under the condition of charge neutrality and β stability (µ n = µ p + µ e ). The nuclear clusters are assumed to be arranged in a bcc lattice which are approximated by Wigner-Seitz cells defined as spheres. Electrons are extremely relativistic and are assumed to be uniformly distributed in the cell. Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

NS crust in the presence of B The equilibrium nuclei present in the Neutron Star Inner Crust as a function of density with and without magnetic field are determined using BLV separation procedure. [Bonche, Levit and Vauthetin NPA 427(1984) 278] Most Stable nuclei as a function of baryon density is determined by minimizing the free energy under the condition of beta equilibrium and charge neutrality. Strong magnetic fields enhance the proton fraction in the inner crust of a neutron star. It also increases the charge and mass number of nuclei present in the inner crust. Free energy is lower as compared to the non-magnetic case which suggests that the nuclei are more stable in presence of strong magnetic fields. Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Decompressed Matter at NSE Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

NSE Reference: A. Odrzywolek. “NSE abundance data”, Atomic Data and Nuclear Data Tables, 98: (2012) Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

NSE

NSE Results Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Result Nuclei are more abundant at low temperature. Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Result

Result Abundance of nuclei increases with increasing mass density Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Result

Result

Result

Coulomb correction term Reference: M. Kostka et al, “R-Java 2.0: the nuclear physics” [arXiv: v1] Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Reference: 1. S. Goriely et al, “The decompression of the outer star crust & r-process nucleosynthesis”, Potekhin & Chabrier, “Equation of state of fully ionized electron-ion plasmas. II. Extension to relativistic densities & to the solid phase”, 2002 Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Adding the Coulomb corrections to the binding energy in eqn. (3), we solve eqns. (1) & (2) by N-R method to find the proton & neutron fraction which are used to calculate mass abundance. Then the number abundances of nuclei are calculated using eqn. (4). Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Result Result (Considering Coulomb correction)  From these figures, it can be seen that abundance increases slightly for higher temperature when we consider Coulomb corrections.  There’s no much effect of Coulomb correction on abundance for low T. With Coulomb “ ” Without Coulomb “ “ With Coulomb “ ” Without Coulomb “ ” With Coulomb “ ” Without Coulomb “ ” Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Result Result (Considering Coulomb correction)  It is clear from these figures that nuclei abundance increases slightly for lower density when we consider Coulomb corrections.  Inclusion of Coulomb correction has no effect on abundance for higher density. With Coulomb “ ” Without Coulomb “ ” With Coulomb “ ” Without Coulomb “ ” With Coulomb “ ” Without Coulomb “ ” Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Result Result (Considering Coulomb correction) With Coulomb “ ” Without Coulomb “ ” With Coulomb “ ” Without Coulomb “ ” With Coulomb “ ” Without Coulomb “ ” Advances in Astroparticle Physics and Cosmology (AAPCOS 2015), SINP, Kolkata

Summary

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