6,634 research outputs found
Conditions for Phase Equilibrium in Supernovae, Proto-Neutron and Neutron Stars
We investigate the qualitative properties of phase transitions in a general
way, if not the single particle numbers of the system but only some particular
charges like e.g. baryon number are conserved. In addition to globally
conserved charges we analyze the implications of locally conserved charge
fractions, like e.g. local electric charge neutrality or locally fixed proton
or lepton fractions. The conditions for phase equilibrium are derived and it is
shown, that the properties of the phase transition do not depend on the locally
conserved fractions. Finally, the general formalism is applied to the
liquid-gas phase transition and the hadron-quark phase transition for typical
astrophysical environments like in supernovae, proto-neutron or a neutron
stars. We demonstrate that the Maxwell construction known from
cold-deleptonized neutron star matter with two locally charge neutral phases
requires modifications and further assumptions concerning the applicability for
hot lepton-rich matter. All possible combinations of local and global
conservation laws are analyzed, and the physical meaningful cases are
identified. Several new kinds of mixed phases are presented, as e.g. a locally
charge neutral mixed phase in proto-neutron stars which will disappear during
the cooling and deleptonization of the proto-neutron star.Comment: 18 page
Deconfinement to Quark Matter in Neutron Stars - The Influence of Strong Magnetic Fields
We use an extended version of the hadronic SU(3) non-linear realization of
the sigma model that also includes quarks to study hybrid stars. Within this
approach, the degrees of freedom change naturally as the temperature/density
increases. Different prescriptions of charge neutrality, local and global, are
tested and the influence of strong magnetic fields and the anomalous magnetic
moment on the particle population is discussed.Comment: To appear in the proceedings of conference XII HADRON PHYSICS April,
22-27, 2012, Bento Goncalves, Wineyards Valley Region, Rio Grande do Sul,
Brazil Revised version with corrections made to the text in page
The Star Cluster Population in the Tidal Tails of NGC 6872
We present a photometric analysis of the rich star cluster population in the
tidal tails of NGC 6872. We find star clusters with ages between 1 - 100 Myr
distributed in the tidal tails, while the tails themselves have an age of less
than 150 Myr. Most of the young massive ()
clusters are found in the outer regions of the galactic disk or the tidal
tails. The mass distribution of the cluster population can be well described by
power-law of the form , where , in very good agreement with other young cluster populations found in a
variety of different environments. We estimate the star formation rate for
three separate regions of the galaxy, and find that the eastern tail is forming
stars at times the rate of the western tail and times the
rate of the main body of the galaxy. By comparing our observations with
published N-body models of the fate of material in tidal tails in a galaxy
cluster potential, we see that many of these young clusters will be lost into
the intergalactic medium. We speculate that this mechanism may also be at work
in larger galaxy clusters such as Fornax, and suggest that the so-called
ultra-compact dwarf galaxies could be the most massive star clusters that have
formed in the tidal tails of an ancient galactic merger.Comment: 12 pages, 10 figures, accepted A&
A new possible quark-hadron mixed phase in protoneutron stars
The phase transition from hadronic matter to quark matter at high density
might be a strong first order phase transition in presence of a large surface
tension between the two phases. While this implies a constant-pressure mixed
phase for cold and catalyzed matter this is not the case for the hot and lepton
rich matter formed in a protoneutron star. We show that it is possible to
obtain a mixed phase with non-constant pressure by considering the global
conservation of lepton number during the stage of neutrino trapping. In turn,
it allows for the appearance of a new kind of mixed phase as long as neutrinos
are trapped and its gradual disappearance during deleptonization. This new
mixed phase, being composed by two electric neutral phases, does not develop a
Coulomb lattice and it is formed only by spherical structures, drops and
bubbles, which can have macroscopic sizes. The disappearance of the mixed phase
at the end of deleptonization might lead to a delayed collapse of the star into
a more compact configuration containing a core of pure quark phase. In this
scenario, a significant emission of neutrinos and, possibly, gravitational
waves are expected.Comment: 4 pages, 4 figure
Some properties of convection in hybrid stars
It is shown that the unusual thermodynamic properties of matter within the
region of two-phase coexistence in hybrid stars result in a change of the
standard condition for beginning of convection. In particular, the thermal flux
transported by convection may be directed towards the stellar center. We
discuss favorable circumstances leading to such an effect of "inverse
convection" and its possible influence on the thermal evolution of hybrid
stars.Comment: 13 pages, 3 figures. The discussion is extended according to referees
suggestions. New references added. Accepted to MNRA
Mass, radius, and composition of the outer crust of nonaccreting cold neutron stars
The properties and composition of the outer crust of nonaccreting cold
neutron stars are studied by applying the model of Baym, Pethick, and
Sutherland, which was extended by including higher order corrections of the
atomic binding, screening, exchange and zero-point energy. The most recent
experimental nuclear data from the atomic mass table of Audi, Wapstra, and
Thibault from 2003 is used. Extrapolation to the drip line is utilized by
various state-of-the-art theoretical nuclear models (finite range droplet,
relativistic nuclear field and non-relativistic Skyrme Hartree-Fock
parameterizations). The different nuclear models are compared with respect to
the mass and radius of the outer crust for different neutron star
configurations and the nuclear compositions of the outer crust.Comment: 5 pages, 2 figures, submitted to J. Phys. G, part of the proceedings
of the Nuclear Physics in Astrophysics III conference in Dresde
Dynamical Systems On Three Manifolds Part II: 3-Manifolds,Heegaard Splittings and Three-Dimensional Systems
The global behaviour of nonlinear systems is extremely important in control
and systems theory since the usual local theories will only give information
about a system in some neighbourhood of an operating point. Away from that
point, the system may have totally different behaviour and so the theory
developed for the local system will be useless for the global one.
In this paper we shall consider the analytical and topological structure of
systems on 2- and 3- manifolds and show that it is possible to obtain systems
with 'arbitrarily strange' behaviour, i.e., arbitrary numbers of chaotic
regimes which are knotted and linked in arbitrary ways. We shall do this by
considering Heegaard Splittings of these manifolds and the resulting systems
defined on the boundaries.Comment: 15 pages with 9 pictures. Accepted by Int. J. of Bifurcation and
Chao
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