Roberto Aquilano

The luminosity oscillation of X-ray bursters and recurrent novae

Abstract‘Thermo-mechanical’ oscillations of a radiating spherically-symmetric shell containing a fermion gas (i.e., oscillation where only mechanical, thermodynamical, and eventually radiation phenomena are taken into account) are studied. With a reasonable choice of the three relevant parameters all other observational data are similar to the ones of X-ray bursters and recurrent novae.Therefore, thermo-mechanical oscillations could play an important role in the oscillation spectrum of these astronomical objects.

ON THE DYNAMICAL EQUATION OF A SPHERICAL RADIATING SHELL AND THE OSCILLATING STARS

A classical and post-Newtonian model of pulsating star is studied. The condition for an oscillating behavior and the corresponding period are computed.

SPHERICALLY SYMMETRIC RADIATING SHELLS AND POST-NEWTONIAN APPROXIMATION

A recipe to use post-Newtonian approximation in the case of the shell dynamics is found. The obtained motion equation coincide with the exact one.

Entropy gap and time asymmetry. 2.

In this letter the paper [R. Aquilano and M. Castagnino, Mod. Phys. Lett.A11, 755 (1996)] is improved by considering that the main source of entropy production is the star photospheres.

The Post-Newtonian Approximation and the Shells Oscillations

We use the post-Newtonian approximation to show that the shells oscillations could be very important in the physics of astronomical objects with neutron stars. The conclusions of Ref. 1 are confirmed.

SHELLS OSCILLATIONS AND RELATIVISTIC EFFECTS

In this letter we show that the shells oscillations could play an important role in the physics of X-ray bursters. We use the post-Newtonian approximation in this case and the conclusions of Ref. 1 are confirmed.

OSCILLATTONS AND STRANGE STARS

We present a model of a remnant of supernova, with a strange matter star, and in this state we introduce radial oscillations. We obtain a strange-pulsar with millisecond oscillations.

Addendum to “Mathematical structure of quantum superspace as a consequence of time asymmetry”

In this paper we improve the results of sec. VI of paper [M. Castagnino, Phys. Rev. D 57, 750 (1998)] by considering that the main source of entropy production are the photospheres of the stars.

THE ENTROPY GAP AND THE TIME ASYMMETRY

The universe time-asymmetry is essentially produced by its low-entropy unstable initial state. Using quanlitative arguments, Paul Davies has demonstrated that the universe expansion may diminish the entropy gap, therefore explaining its low-entropy state, with respect to the maximal possible entropy at any time. This idea is implemented in a qualitative way\thinspace in a simple homogeneous model. Some rough coincidence with observational data are found

On the dynamical equation of a spherical radiating shell

The thermomechanical oscillations of a radiating spherical shell are studied. With a reasonable choice of parameters this simple model reproduces the behaviour of X-ray bursters and recurrent novae. Different hypotheses on the radiation pressure are introduced and the problem is studied at the classical and post-newtonian levels.