Relativistic hybrid stars with sequential first-order phase transitions and heavy-baryon envelopes

Abstract

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 ∆-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 2SC and CFL color 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 ∆-resonance degrees of freedom, as well as the deconfinement phase transition at sufficiently low density, produce 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 ∆-resonance-hyperon admixed phase or/and the quark phase(s) is favored by this 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 star 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.

Discontinuity gravity modes in hybrid stars: Assessing the role of rapid and slow phase conversions

“…Notice that all the hybrid models of Table I allow the existence of twin objects, i.e., couples of stars with the same gravitational mass but different radii. This is a very relevant signature that may be used to scrutinize the internal composition of compact objects [8,10,[51][52][53][54]. In fact, new missions probing neutron star radii such as Neutron Star Interior Composition Explorer (NICER) will be able to measure NS radii with 5%-10% uncertainty, while the future enhanced X-ray Timing and Polarimetry (eXTP) is expected to have even better precision.…”

Light clusters in dilute heavy-baryon admixed nuclear matter

“…The formation of the heavy baryons in dense and cold nuclear matter, in particular hyperonic members of the J 1/2+ baryonic octet in combinations with the non-strange members of baryon J 3/2+ decouplet (Δ-resonances) has attracted attention in recent years [55][56][57][58][59][60][61][62][63][64]. The relativistic density functionals were successfully tuned to remove the tension between the softening of the equation of state of dense matter associated with the onset of the baryons and the astrophysical observations of the massive neutron stars with masses 2M [58][59][60].…”

Accretion‐induced collapse to third family compact stars as trigger for eccentric orbits of millisecond pulsars in binaries

“…For the present scenario, it is not immediately obvious how more massive eMSPs could be explained like PSR J1946 + 3417 (Barr et al ) with a precisely determined high mass of 1.828(22) M ⊙ . It is, however, also possible to develop the present scenario further so that another major structural rearrangement contributing to a pulsar kick may take place, even leading from a third to a fourth family (see Alford & Sedrakian ; Li et al ).…”

“…They confirm the trend of the present model: larger mass entails higher spin frequency high mass of 1.828( 22) M ⊙ . It is, however, also possible to develop the present scenario further so that another major structural rearrangement contributing to a pulsar kick may take place, even leading from a third to a fourth family (see Alford & Sedrakian 2017;Li et al 2019).…”