Nucleosynthesis in Strange Star Mergers

The possible existence of deconfined matter in the cores of neutron stars has been studied for over three decades without a firm indication either for or against this proposition. Analysis mostly rely on the comparison of mass-radius curves obtained for different compositions with observational data on the mass of the most massive objects of this kind accurately determined. Nevertheless, there are other possibilities for indirectly studying the internal composition of this class of compact objects, e.g, analyzing cooling behavior, X-ray bursts, supernova’s neutrinos. We present calculations on the expected nucleosynthesis spectra for the strange star-strange star merger scenario as means to test the strange quark matter hypothesis and its realization inside such objects. This would result very different from the typical r-process nucleosynthesis expected in neutron star mergers since the high temperature deconfinement of strange matter would produce large amounts of neutrons and protons and the mass buildup would proceed in a Big-Bang nucleosynthesis like scenario. The neutron to proton ratio would allow to reach the iron peak only, a very different prediction from the standard scenario. The resultant light curve indicate it may be compatible with that of a kilonova depending on the specific details of the ejecta.Facultad de Ciencias Astronómicas y Geofísica

Strangelet spectra from type II supernovae

We study in this work the fate of strangelets injected as a contamination in the tail of a ‘‘strange matterdriven’’ supernova shock. A simple model for the fragmentation and braking of the strangelets, when they pass through the expanding oxygen shell is presented and solved to understand the reprocessing of this component. We find that the escaping spectrum is a scaled-down version of the one injected at the base of the oxygen shell. The supernova source is likely to produce low-energy particles of A∼100– 1000 quite independently of the initial conditions. However, it is difficult that ultrarrelativistic strangelets (such as the hypothetical Centauro primaries) can have an origin in those explosive events.Facultad de Ciencias Astronómicas y Geofísica

Strange-pulsar evolution and soft γ-repeaters

Soft γ-repeaters are puzzling sources which produce γ-transients, and which have been tentatively identified as a separate subclass from sources which produce «classical» γ-bursts. We sketch the features of a model for soft γ-repeaters based on the evolutionary history of strange pulsars. It is shown that the main features of soft γ-repeaters can be explained by strange-pulsar evolutionFacultad de Ciencias ExactasFacultad de Ciencias Astronómicas y Geofísica

Nucleosynthesis in Strange Star Mergers

The possible existence of deconfined matter in the cores of neutron stars has been studied for over three decades without a firm indication either for or against this proposition. Analysis mostly rely on the comparison of mass-radius curves obtained for different compositions with observational data on the mass of the most massive objects of this kind accurately determined. Nevertheless, there are other possibilities for indirectly studying the internal composition of this class of compact objects, e.g, analyzing cooling behavior, X-ray bursts, supernova’s neutrinos. We present calculations on the expected nucleosynthesis spectra for the strange star-strange star merger scenario as means to test the strange quark matter hypothesis and its realization inside such objects. This would result very different from the typical r-process nucleosynthesis expected in neutron star mergers since the high temperature deconfinement of strange matter would produce large amounts of neutrons and protons and the mass buildup would proceed in a Big-Bang nucleosynthesis like scenario. The neutron to proton ratio would allow to reach the iron peak only, a very different prediction from the standard scenario. The resultant light curve indicate it may be compatible with that of a kilonova depending on the specific details of the ejecta.Facultad de Ciencias Astronómicas y Geofísica

Can a phase transition of nuclear matter to quarks strange matter trigger the explosion of supernovae of type II?

It was speculated (Witten, 1984) about the possibility that quarks (u,d,s) strange matter will be the fundamental level of the hadronic matter. If this is true, it seems possible the existence of transitions of exothermic phases of nuclear matter to strange matter. The conditions reached at the nucleus post-bounce epoch for a supernova of type II should be adequate for this process to take place. Assuming the existence of this transition we present the consequences of an explosion under these conditions. We used a gas at a finite temperature as equation of state for the quarks matter, while for the nuclear matter we used the equation of state for free neutrons as also the model of Bethe-Johnson. We conclude that in both situations the process is possible and it may be the responsible for the type II supernova explosions.Asociación Argentina de Astronomí

Does PSR J1417-4402 system behave as a "Redback"?

We study the present evolutionary status of the binary system containing the 2.66 ms pulsar PSR J1417-4402 in a 5.4 day orbit. This is the pulsar in the original source 3FGL J1417.5-4402, that has undergone a transition from X-ray state to a pulsar state, just like some redbacks did. The system has many characteristics similar to redback pulsars family, but is on a much wider orbit. We show that close binary evolution including irradiation feedback driven by the luminosity due to accretion onto the neutron star component of the pair, and evaporation due to pulsar emission, is able to account for the masses of the components and the photometric data of the donor star. The tracks leading to the present PSR J1417-4402 are degenerate within a range of parameters, suggesting that the same physics invoked to explain the redback/black widows groups leads to the formation of much wider orbit systems, outside the redback region limits.Facultad de Ciencias Astronómicas y Geofísica

Identifying the formation mechanism of redback pulsars

We analyse the evolution of close binary systems containing a neutron star that lead to the formation of redback pulsars. Recently there has been some debate on the origin of such systems and the formation mechanism of redbacks may still be considered as an open problem. We show that the operation of a strong evaporation mechanism, starting from the moment when the donor star becomes fully convective (or alternatively since the formation of the neutron star by accretion induced collapse), produces systems with donor masses and orbital periods in the range corresponding to redbacks with donors appreciably smaller than their Roche lobes, i.e., they have low filling factors (lower than 0.75). Models of redback pulsars can be constructed assuming the occurrence of irradiation feedback. They have been shown to undergo cyclic mass transfer during the epoch at which they attain donor masses and orbital periods corresponding to redbacks, and stay in quasi-Roche lobe overflow conditions with high filling factors. We show that, if irradiation feedback occurs and radio ejection inhibits further accretion onto the neutron star after the first mass transfer cycle, the redback systems feature high filling factors. We suggest that the filling factor should be considered as a useful tool for discriminating among those redback formation mechanisms. We compare theoretical results with available observations, and conclude that observations tend to favour models with high filling factors.Instituto de Astrofísica de La Plat

Magnetic color-flavor-locked stars

Using the solutions of the gap equations of the magnetic-color-flavor-locked (MCFL) phase of paired quark matter in a magnetic field, and taking into consideration the separation between the longitudinal and transverse pressures due to the field-induced breaking of the spatial rotational symmetry, the equation of state (EoS) of the MCFL phase is self-consistently determined. Implications for stellar models of magnetized (self-bound) strange stars and hybrid (MCFL core) stars are discussed.FAPESPCNPqOffice of Nuclear Theory of the Department of Energy de-sc000217