S. M. Chitre

A dust model for the cosmic microwave background

The cosmic microwave background may be explained on the basis of absorption and reemission of the light from galaxies by graphite whiskers of lengthsl≃0.1-1 mm. The mass density of such particles required is of the order of 10−34 g cm−3.

The effect of intergalactic dust on the measurement of the cosmological deceleration parameterq0

In a recent attempt to explain the cosmic microwave background without the big bang, a thermalization mechanism involving intergalactic whisker grains of graphite was proposed. The effect of absorption by the intergalactic medium in general, and of the above type in particular, on the measurement of the deceleration parameterq0 of the expanding universe is discussed. Its effect is shown to be comparable in magnitude but opposite to that of the luminosity evolution in galaxies. A consequential selection effect is also discussed.

INFRARED EMISSION FROM X-RAY SOURCES

The infrared emission from some X-ray sources is attributed to proton—cyclotron masering process operating near the polar regions of an accreting neutron star in a binary system.

A model for the rapid X-ray Burster

A model for the Rapid X-ray Burster (MXB 1730-333) based on an accreting rotating magnetized neutron star in a binary system is proposed. The bursts are attributed to instabilities produced at an equilibrium surface above the poles of the neutron star, which is created by the infalling gas supported by a combination of radiation and relativistic gas pressures. The special feature of the proposed model is that, when accretion onto the poles is prevented by radiation pressure, relativistic gas streams out of the polar region.

Gravitational screens and superluminal separation in quasars

The differential bending of radio waves by a suitably placed gravitational screen such as an intervening galaxy can lead to large magnification of the separation velocity of the components in the nuclear region of a quasar. It is suggested tha the apparent superluminal separation of such components observed in some quasars by the VLBI techniques could be due to velocity magnifications of this type. The astrophysical feasibility of this explanation is critically examined, and an optical search for objects of large mass-to-light ratio en route to quasars showing superluminal separation is advocated.

Infrared bursts from liller I/MXB 1730-333

The observation of infrared bursts from the globular cluster Liller I has been reported by Kulkarniet al. (1979) and confirmed by Joneset al. (1980). The infrared bursts which resemble Type I X-ray bursts in their characteristics are plausibly attributed to a cyclotron maser instability operating at few tens of neutron star radii above the poles of a magnetized neutron star in a binary system. It is suggested that similar infrared bursts should in general be observable from Type I X-ray burst sources.

Diffusion Coefficients of Nucleons in the Inhomogeneous Big Bang Model

There is a strong possibility that a first order QCD phase transition from the quark-gluon plasma to the confined hadronic matter had occurred in the early universe when the temperature was about 100 MeV. This phase transition might have produced isothermal baryon number fluctuations [1,2,3]. Applegate and Hogan [2,3] have suggested that the characteristic size of these fluctuations could be such that protons would not be able to diffuse across them before the onset of nucleosynhthesis, but the neutrons would as they have no electrical charge and therefore suffer less scattering. Their calculations have shown that the difference in the mean free paths of neutrons and protons and the resultant diffusive segregation influences the formation of the light elements very significantly.In ref. [3] the diffusion coeffficients were calculated using a mobility formula and the Einstein relation between mobility and the diffusion coefficient [4]. We calculate the diffusion coefficients in the framework of relativistic kinetic theory [5] in the temperature range 108 ≤ T ≤ 5.109 °K, assuming all particles to be classical. For these temperatures neutrons and protons are no longer in equilibrium with respect to weak interactions and as a result they retain their identity for diffusive segregation to take place.Neutrons are scattered by electrons through the interaction of their magnetic moments and by protons due to nuclear interaction.Protons,on the other hand, undergo Coulomb scattering by electrons and are also scattered by neutrons.With these elementary cross-sections as input we calculate the neutron-electron and neutron-proton diffusion coefficients using the first order Chapman-Enskog expressions [5].

Faster-than-light motion in quasars

Over the past fifteen years, observations of some quasars with the techniques of very-long-baseline interferometry have shown that the angular separation between pairs of radio-emitting regions in their cores is increasing year after year. If the quasars are indeed as far away as implied by Hubble’s law, then these angular motions translate into linear speeds several times the speed of light. Several theoretical scenarios have been proposed to show that the observed motions are illusory. The leading contender in this field — the relativistic beam model — and an alternative offered by the concept of a gravitational screen are described and compared in the light of recent observational data.

Partition functions of nuclei in Hartree-Fock approximation

Thermodynamic properties of an excited iron-peaked nucleus are calculated in the framework of a self-consistent temperature-dependent Hartree-Fock theory using the Skyrme effective interaction. It is found that for temperatures up to 10 MeV, the nuclei have a substantially higher internal energy and lower entropy per particle than previous calculations. The thermodynamic implications for gravitational collapse are discussed.

Composition and adiabatic index of matter at high temperatures

The equation of state and the adiabatic index of thermally dissociated matter composed of nucleons, electrons, positrons, neutrinos, antineutrinos and photons are calculated in the density and temperature ranges, 109≲q(g cm−3)≲1013, 2×1010≲T K≲5×1011, respectively. The interaction between nucleons is explicitly included. This leads to a softening of the equation of state. The implications of the results for the problem of supernova collapse are discussed.