14 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.
Effects of color superconductivity on the structure and formation of compact stars
We show that if color superconducting quark matter forms in hybrid or quark
stars it is possible to satisfy most of recent observational boundaries on
masses and radii of compact stellar objects. An energy of the order of
erg is released in the conversion from a (metastable) hadronic star
into a (stable) hybrid or quark star in presence of a color superconducting
phase. If the conversion occurs immediately after the deleptonization of the
proto-neutron star, the released energy can help Supernovae to explode. If the
conversion is delayed the energy released can power a Gamma Ray Burst. A delay
between the Supernova and the subsequent Gamma Ray Burst is possible, in
agreement with the delay proposed in recent analysis of astrophysical data.Comment: 4 pages, 2 figures. To be published in Phys.Rev.
The supernova-GRB connection
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 1053 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. Possible experimental evidences, indicating a range of time delay between a Supernova explosion and a subsequent Gamma Ray Burst, are here discussed and interpreted
Gamma ray bursts and the transition to quark matter in compact stars
We discuss a model for long Gamma-Ray-Bursts in which the central engine is associated with the conversion process of a metastable hadronic star into a star containing quark matter. We analyze the observational signatures of the model, i.e. the Supernova-GRB temporal connection and the existence of long quiescent times in the temporal structure of Gamma-Ray-Bursts
Early appearance of Δ isobars in neutron stars
We discuss the formation of Δ isobars in neutron star matter. We show that their threshold density strictly correlates with the density derivative of the symmetry energy of nuclear matter: the L parameter. By restricting L to the range of values indicated by recent experimental and theoretical analysis, i.e., 40MeV≲L≲62MeV, we find that Δ isobars appear at a density of the order of 2 to 3 times the nuclear matter saturation density, i.e., the same range as for the appearance of hyperons. The range of values of the couplings of the Δs with the mesons is restricted by the analysis of the data obtained from photoabsorption, electron and pion scattering on nuclei. If the potential of the Δ in nuclear matter is close to the one indicated by the experimental data then the equation of state becomes soft enough that a “Δ puzzle” exists, similar to the “hyperon puzzle” widely discussed in the literature. Possible solutions to this puzzle are also discussed
Dense hadronic matter in neutron stars
The existence of stars with masses up to 2M and the hints of the existence
of stars with radii smaller than 11 km seem to require, at the same
time, a stiff and a soft hadronic equation of state at large densities. We
argue that these two, apparently contradicting, constraints are actually an
indication of the existence of two families of compact stars: hadronic stars
which could be very compact and quark stars which could be vary massive.
In this respect, a crucial role is played, in the hadronic equation of state, by the delta isobars whose early appearance shifts to large densities the formation of hyperons. We also discuss how recent experimental information on the symmetry energy of nuclear matter at saturation indicates, indirectly, an early appearance of delta isobars in neutron star matter