49 research outputs found
Color Superconductivity in Compact Stars and Gamma Ray Bursts
We study the effects of color superconductivity on the structure and
formation of compact stars. We show that it is possible to satisfy most of
recent observational boundaries on masses and radii if a diquark condensate
forms in a hybrid or a quark star. Moreover, we find that a huge amount of
energy, of the order of erg, can be released in the conversion from a
(metastable) hadronic star into a (stable) hybrid or quark star, if the
presence of a color superconducting phase is taken into account. Accordingly to
the scenario proposed in Astrophys.J.586(2003)1250, the energy released in this
conversion can power a Gamma Ray Burst. This mechanism can explain the recent
observations indicating a delay, of the order of days or years, between a few
Supernova explosions and the subsequent Gamma Ray Burst.Comment: 15 pages, 4 figures, 1 tabl
Formation of Quark Phases in compact stars and their connection to Gamma-Ray-Bursts
We analyse the occurrence of quiescent times in the temporal structure of the
Gamma-Ray-Bursts (GRBs) light curves. We show that if a long quiescent time is
present, it is possible to divide the total duration of GRBs into three
periods: the pre-quiescence emission, the quiescent time and the
post-quiescence emission. We then discuss a model of the GRBs inner engine
based on the formation of quark phases during the life of an hadronic star.
Within this model the pre-quiescence emission is interpreted as due to the
deconfinement of quark inside an hadronic star and the formation of 2SC quark
matter. The post-quiescence emission is due to the conversion of 2SC into the
Color-Flavor-Locking (CFL) phase. The temporal delay between these two
processes is connected with the nucleation time of the CFL phase in the 2SC
phase and it can be associated with the observed quiescent times in the GRBs
light curves. The stability of CFL cores in compact stars is also discussed.Comment: 6 pages, 3 figures, to appear in the proceedings of 3th International
Conference on Nuclear Physics in Astrophysics (NPAIII), 26 - 31 March 2007
Dresden, German
Bulk Viscosity in Hybrid Stars
We compute the bulk viscosity of a mixed quark-hadron phase. In the first
scenario to be discussed, the mixed phase occurs at large densities and we
assume that it is composed of a mixing of hyperonic matter and quarks in the
Color Flavor Locked phase. In a second scenario, the mixed phase occurs at
lower densities and it is composed of a mixing of nucleons and unpaired quark
matter. We have also investigated the effect of a non-vanishing surface tension
at the interface between hadronic and quark matter. In both scenarios, the bulk
viscosity is large when the surface tension is absent, while the value of the
viscosity reduces in the second scenario when a finite value for the surface
tension is taken into account. In all cases, the r-mode instabilities of the
corresponding hybrid star are suppressed.Comment: 8 pages, 7 figures, extended version in print on Phys.Rev.
Magnetic field generated by r-modes in accreting quark stars
We show that the r-mode instability can generate strong toroidal fields in
the core of accreting millisecond quark stars by inducing differential
rotation. We follow the spin frequency evolution on a long time scale taking
into account the magnetic damping rate in the evolution equations of r-modes.
The maximum spin frequency of the star is only marginally smaller than in the
absence of the magnetic field. The late-time evolution of the stars which enter
the r-mode instability region is instead rather different if the generated
magnetic fields are taken into account: they leave the millisecond pulsar
region and they become radio pulsars.Comment: 8 pages, 8 figure
Formation of quark phases in compact stars and SN explosion
We describe possible scenarios of quark deconfinement in compact stars and we
analyze their astrophysical implications. The quark deconfinement process can
proceed rapidly, as a strong deflagration, releasing a huge amount of energy in
a short time and generating an extra neutrino burst. If energy is transferred
efficiently to the surface, like e.g. in the presence of convective
instabilities, this burst could contribute to revitalize a partially failed SN
explosion. We discuss how the neutrino observations from SN1987A would fit in
this scenario. Finally, we focus on the fate of massive and rapidly rotating
progenitors, discussing possible time separations between the moment of the
core collapse and the moment of quark deconfinement. This mechanism can be at
the basis of the interpretation of gamma ray bursts in which lines associated
with heavy elements are present in the spectrum.Comment: 9 pages, 3 figures, Proceedings "6th International Conference on
Perspectives in Hadronic Physics", May 2008, Triest
Equation of state at high densities and modern compact star observations
Recently, observations of compact stars have provided new data of high
accuracy which put strong constraints on the high-density behaviour of the
equation of state of strongly interacting matter otherwise not accessible in
terrestrial laboratories. The evidence for neutron stars with high mass (M =2.1
+/- 0.2 M_sun for PSR J0751+1807) and large radii (R > 12 km for RX J1856-3754)
rules out soft equations of state and has provoked a debate whether the
occurence of quark matter in compact stars can be excluded as well. In this
contribution it is shown that modern quantum field theoretical approaches to
quark matter including color superconductivity and a vector meanfield allow a
microscopic description of hybrid stars which fulfill the new, strong
constraints. The deconfinement transition in the resulting stiff hybrid
equation of state is weakly first order so that signals of it have to be
expected due to specific changes in transport properties governing the
rotational and cooling evolution caused by the color superconductivity of quark
matter. A similar conclusion holds for the investigation of quark deconfinement
in future generations of nucleus-nucleus collision experiments at low
temperatures and high baryon densities such as CBM @ FAIR.Comment: 6 pages, 2 figures, accepted for publication in J. Phys. G. (Special
Issue