Neutron stars components

As just described, the most precise measurements of masses come from double neutron star systems. There are currently five such systems known, three of which will coalesce due to gravitational radiation in less than the age of the universe, 1010 yr (Taylor 1994). These three systems in particular allow very precise measurements of the masses of the components, which are between 1.33 M and 1.45 M0 (Thorsett Chakrabarty 1999). The other two double neutron star systems also have component masses consistent with a canonical 1.4 M . It has been suggested that the tight grouping of masses implies that the maximum mass of a neutron star is 1.5 M0 (Bethe Brown 1995). However, it is important to remember that double neutron star systems all have the same evolutionary pathway and thus the similar masses may simply be the result of a narrow selection of systems. 

In section I we consider the dynamics of rotation of a two-component neutron star and obtain the relaxation solutions for spin-down rate of the star. In section II we compare our solutions for the relaxation process with the observation data from the Vela pulsar. 

Let us consider the rotational dynamics of a two-component neutron star taking into account the pinning and depinning of neutron vortices. Equations of motion of the superfluid and normal components have the following forms [15, 17] ... 

However, a more realistic model for the phase transition between baryonic and quark phase inside the star is the Glendenning construction [16], which determines the range of baryon density where both phases coexist. The essential point of this procedure is that both the hadron and the quark phase are allowed to be separately charged, still preserving the total charge neutrality. This implies that neutron star matter can be treated as a two-component system, and therefore can be parametrized by two chemical potentials like electron and baryon chemical potentials [if. and iin. The pressure is the same in the two phases to ensure mechanical stability, while the chemical potentials of the different species are related to each other satisfying chemical and beta stability. The Gibbs condition for mechanical and chemical equilibrium at zero temperature between both phases reads... 

We shall consider the behavior of the magnetic field at distances r much larger than Ap and Aq. Also we take into account that Aq < Ap < a, Aq < p < R and q < Ar> < R — a. Therefore the components of the magnetic field in the different regions of neutron star are for r < a... 

The value of the compactification radius, Rc In the present approach this radius was a free parameter. For demonstration we chose the radius Rc = 0.33 10 13 cm, when the strange A baryon could behave as the first excitation of a neutron. Such an extradimensional object can mimics a compact star with neutrons in the mantle and A s in the core. With smaller Rc the exotic component appears at larger densities - we may run into the unstable region of the hybrid star and the extra dimension remains undetectable. However, with larger Rc the mass gap becomes smaller and the transition happens at familiar neutron star densities. In this way, reliable observations could lead to an upper bound on Rc. 

Figure 2. The dependences of gravitational mass M on central pressure Pc for the sets of EoS with variants HEA(a), Bonn(b) and BJ — V(c). Solid lines correspond to the models of neutron stars without a quark core (the variant of nucleon component is indicated). On an enlarged scale the phase transition area is shown for EoS 3a.

The analysis of nucleosynthesis in hypernovae suggests a possible classification scheme of supernova explosions [111]. In this scheme, core collapse in stars with initial main sequence masses Mms < 25 — 30M leads to the formation of neutron stars, while more massive stars end up with the formation of black holes. Whether or not the collapse of such massive stars is associated with powerful hypernovae ( Hypernova branch ) or faint supernovae ( Faint SN branch ) can depend on additional ( hidden ) physical parameters, such as the presupernova rotation, magnetic fields. [39], or the GRB progenitor being a massive binary system component [145, 117]. The need for other parameters determining the outcome of the core collapse also follows from the continuous distribution of C+O cores of massive stars before the collapse, as inferred from observations, and strong discontinuity between masses of compact remnants (the mass gap between neutron stars and black holes) [28]2. 

The second equality makes use of the fact that the volume per unit and the number density are inversely related, v = p dv = —p dp. The final equality separates the isoscalar component of the pressure (the only term present for symmetric matter) from that originating from neutron/proton asymmetry. At large asymmetries, the second term dwarfs the first, so it is this term that is principally responsible for resisting the gravitational collapse of a neutron star. 

Thus the 13 C neutron source (with a little assistance from 22Ne) in thermally pulsing low- and intermediate-mass stars is well established as the chief source of the main component of s-process nuclides in the Solar System. It is not quite clear, however, whether the r0 parameter is something unique, or just the average over a more-or-less broad distribution of values nor is it clear why a similar s-process pattern is seen in stars that are metal-deficient by factors of up to 100 (see Pagel Tautvaisiene 1997). 

Chromium. The isotopic heterogeneity is limited to this isotope which can be compared with the normal refractory inclusions of Allende. Both Cr dehcits and excesses are formd ranging from -7.6 e to +210 e (Fig. 8b). The fractions showing the highest enrichment in Cr with no correlated effects in Cr, Cr, Cr points towards a nucleosynthetic component, which is 99% pure in Cr. This component is probably the same as the component found in the CV3 inclusions, and which is produced in a neutron-rich nuclear statistical equilibrium in presupemova massive stars. 

The s process builds up an abundance distribution with peaks at mass numbers (A = Z + N) 87,138 and 208 and pronounced even-odd imbalance. The main component of the s process is associated with thermal pulsations of stars in the asymptotic giant branch (1-3 Mq) which produce neutron densities between 10 and 10 cm (Fig. 5.6). 

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