The effects of Δ-isobars on the equation of state of dense matter and structure of compact stars (CSs) are explored within the covariant density functional theory and confronted with the data on tidal deformability (TD) extracted from the GW170817 event. We show that the presence of Δ-isobars substantially softens the tension between the predictions of the hypernuclear density functionals and the inference from the observations of relatively small radius and small TD of canonical-mass CSs. The TDs deduced from GW170817 are compatible with the existence of hypernuclear CSs containing an admixture of Δ-isobars. We thus argue that the GW170817 event is consistent with a merger of a binary CS system having both strangeness (hyperons) and Δ-isobars in the stellar core.

We compute the mass, radius and tidal deformability of stars containing phase transitions from hadronic to quark phase(s). These quantities are computed for three types of hadronic envelopes: purely nuclear, hyperonic, and $\mathrm{\Delta }$-resonance–hyperon admixed matter. We consider either a single first-order phase transition to a quark phase with a maximally stiff equation of state (EOS) or two sequential first-order phase transitions mimicking a transition from hadronic (H) to a quark matter phase followed by a second phase transition to another quark phase. Such a construct emulates the results of the computations of the EOS, which include two-flavor color-superconducting and color-flavor-locked superconducting phases at low and high density. We explore the parameter space which produces low-mass twin and triplet configurations where equal-mass stars have substantially different radii and tidal deformabilities. We demonstrate that while for purely hadronic stiff EOS the obtained maximum mass is inconsistent with the upper limit on this quantity placed by GW170817, the inclusion of the hyperonic and $\mathrm{\Delta }$-resonance degrees of freedom, as well as the deconfinement phase transition at sufficiently low density, produces a configuration of stars consistent with this limit. The obtained hybrid star configurations are in the mass range relevant for the interpretation of the GW170817 event. We compare our results for the tidal deformability with the limits inferred from GW170817 showing that the onset of non-nucleonic phases, such as $\mathrm{\Delta }$-resonance–hyperon admixed phase and/or the quark phase(s), are favored by these data if the nuclear EOS is stiff. Also, we show that low-mass twins and especially triplets proliferate the number of combinations of possible types of stars that can undergo a merger event, the maximal number being six in the case of triplets. The prospects for uncovering the first-order phase transition(s) to and in quark matter via measurements of tidal deformabilities in merger events are discussed.

We examine the possibility that the light companion in the highly asymmetric binary compact object coalescence event GW190814 is a hypernuclear star. We use density functional theory with functionals that have been tuned to the properties of $\mathrm{\Lambda }$ hypernuclei as well as astrophysical constraints placed by the masses of the most massive millisecond pulsars, the mass-radius range inferred from the NICER experiment, and the binary neutron star merger event GW170817. We compute general-relativistic static and maximally rotating Keplerian configurations of purely nucleonic and hypernuclear stars. We find that while nucleonic stars are broadly consistent with a neutron star being involved in GW190814, this would imply no new degrees of freedom in the dense matter up to 6.5 times the nuclear saturation density. Allowing for hyperonization of dense matter, we find that the maximal masses of hypernuclear stars, even for maximal rapidly rotating configurations, are inconsistent with a stellar nature interpretation of the light companion in GW190814, implying that this event involved two black holes rather than a neutron star and a black hole.

2 figures, 1 table, and 5 pagesWe have explored the occurrence of the spherical shell closures for superheavy nuclei in the framework of the relativistic Hartree-Fock-Bogoliubov (RHFB) theory and the shell effects in terms of two-nucleon gaps $\delta_{2n(p)}$. Although the results depend slightly on the forces used, the general set of magic numbers beyond $^{208}$Pb are predicted as Z=120, 138 for protons and N=172, 184, 228 and 258 for neutrons, respectively. Specifically the RHFB calculations favor the nuclide $^{304}$120 as the next spherical doubly magic one beyond $^{208}$Pb. As indicated by the self-consistent calculations, the occurrences of superheavy shell closures are essentially related with the violation and restoration of relativistic pseudo-spin symmetry. Further analysis imply that the shell effects are sensitive to both the values of scalar and nonrelativistic effective masses, which togetherwith the violation of the relativistic symmetry may interpret the origin of model deviations