arXiv subjects

F. Weber

Publications and source records attributed to F. Weber.

77 records · Page 5Linked to original sources

arXiv1997

Signal of Quark Deconfinement in the Timing Structure of Pulsar Spin-Down

The conversion of nuclear matter to quark matter in the core of a rotating neutron star alters its moment of inertia. Hence the epoch over which conversion takes place will be signaled in the spin-down "signal_prl.tex" 581 lines, 22203 characters characteristics of pulsars. We find that an observable called the braking index should be easily measurable during the transition epoch and can have a value far removed (by orders of magnitude) from the canonical value of three expected for magnetic dipole radiation, and may have either sign. The duration of the transition epoch is governed by the slow loss of angular momentum to radiation and is further prolonged by the reduction in the moment of inertia caused by the phase change which can even introduce an era of spin-up. We estimate that about one in a hundred pulsars may be passing through this phase. The phenomenon is analogous to ``bachbending'' observed in the moment of inertia of rotating nuclei observed in the 1970's, which also signaled a change in internal structure with changing spin.

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arXiv1996

Impact of medium effects on the cooling of non-superfluid and superfluid neutron stars

Neutrino emission from the dense hadronic component in neutron stars is subject to strong modifications due to collective effects in the nuclear medium. We implement new estimates of the neutrino emissivities of two processes operating in the nuclear medium into numerical cooling simulations of neutron stars. The first process is the modified Urca process, for which the softening of the pion exchange mode and other polarization effects as well as the neutrino emission arising from the intermediate reaction states are taken into account. The second process concerns neutrino emission through superfluid pair breaking and formation processes. It is found that the medium effects on the emissivity of the modified Urca process result in a strong density dependence, which gives a smooth crossover from the standard to the nonstandard cooling scenario for increasing star masses. For superfluid stars, the superfluid pair breaking and formation processes accelerate mildly both the standard and the nonstandard cooling scenario. This leads to a good agreement between the theoretical cooling tracks and the rather low temperatures observed for objects like PSRs 0833-45 (Vela), 0656+14, and 0630+18 (Geminga). The robustness of our findings against variations in both the underlying equation of state of baryonic matter and the used fast cooling processes is demonstrated. Hence we conclude that the two recalculated neutrino emissivities studied here enable one to reproduce theoretically most of the observed pulsar temperatures by varying the masses of neutron star models.

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arXiv1996

From Quark Matter to Strange Machos

This paper gives an overview of the properties of all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from strange stars to strange dwarfs. In contrast to their non-strange counterparts, --neutron stars and white dwarfs--, their properties are determined by two (rather than one) parameters, the central star density and the density at the base of the nuclear crust. This leads to stellar strange-matter configurations whose properties are much more complex than those of the conventional sequence. As an example, two generically different categories of stable strange dwarfs are found, which could be the observed white dwarfs. Furthermore we find very-low-mass strange stellar objects, with masses as small as those of Jupiter or even lighter planets. Such objects, if abundant enough in our Galaxy, should be seen by the presently performed gravitational microlensing searches.

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arXiv1996

Quark Matter, Massive Stars and Strange Planets

This paper gives an overview of the properties of all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from strange stars to strange dwarfs. In contrast to their non-strange counterparts, --neutron stars and white dwarfs--, their properties are determined by two (rather than one) parameters, the central star density and the density at the base of the nuclear crust. This leads to stellar strange-matter configurations whose properties are much more complex than those of the conventional sequence. As an example, two generically different categories of stable strange dwarfs are found, which could be the observed white dwarfs. Furthermore we find very low-mass strange stellar objects, with masses as small as those of Jupiter or even lighter planets. Such objects, if abundant enough in our Galaxy, should be seen by the presently performed gravitational microlensing searches. Further aspects studied in this paper concern the limiting rotational periods and the cooling behavior of neutron stars and their strange counterparts.

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arXiv1996

Thermal Evolution of Compact Stars

A collection of modern, field-theoretical equations of state is applied to the investigation of cooling properties of compact stars. These comprise neutron stars as well as hypothetical strange matter stars, made up of absolutely stable 3-flavor strange quark matter. Various uncertainties in the behavior of matter at supernuclear densities, e.g., hyperonic degrees of freedom, behavior of coupling strengths in matter, pion and meson condensation, superfluidity, transition to quark matter, absolute stability of strange quark matter, and last but not least the many-body technique itself are tested against the body of observed cooling data.

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