We analyze and quantify how the color-flavor locked (CFL) phase in dense matter enhances the parameter space for absolute stability (strange matter). We find that the “CFL strange matter” phase can be the true ground state of hadronic matter for a much wider range of the parameters of the model (the gap of the QCD Cooper pairs $\Delta ,$ the strange quark mass $m_s,$ and the bag constant $B)$ than the state without any pairing, and derive a full equation of state and an accurate analytic approximation to the lowest order in $\Delta$ and $m_s$ which may be directly used for applications. The effects of pairing on the equation of state are found to be small (as previously expected), but not negligible, and may be relevant for astrophysics.

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 of the MCFL phase is self-consistently determined. This result is then used to investigate the possibility of absolute stability, which turns out to require a field-dependent “bag constant” to hold. That is, only if the bag constant varies with the magnetic field, there exists a window in the magnetic field vs bag constant plane for absolute stability of strange matter. Implications for stellar models of magnetized (self-bound) strange stars and hybrid (MCFL core) stars are calculated and discussed.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

Context. Recently, Doroshenko and collaborators reported a very low-mass compact star, a Central Compact Object named XMMU J173203.3−344518 inside the supernova remnant HESS J1731−347. Its tiny mass is at odds with all calculations of minimum masses of neutron stars generated by iron cores, therefore (and even if not compellingly) it has been suggested to be a “strange star”. In addition to the mass, the radius and surface temperature were extracted from the data, and the whole body of information should ultimately reveal whether this object is truly consistent with an exotic composition. Aims. Our aim is to understand the status of the compact object XMMU J173203.3−344518 in HESS J1731−347 within the existing models of strange stars, including its prompt formation. Methods. The information obtained on the mass, radius and surface temperature are compared to theoretical calculations performed within usual theoretical models using General Relativity as the assumed theory of gravitation and a handful of cooling scenarios. A qualitative discussion showing the consistency of the strange-matter driven supernova scenario with a low-mass compact star is provided. Results. We found that the object HESS J1731−347 fits within the same quark star models recently employed to explain the masses and radii of the NICER objects PSR J040+6620 and PSR J0030+0451, in which both quantities were simultaneously determined. It is also remarkable to find that a simple cooling scenario devised 30 yr ago with superconducting quarks provides an overall good explanation of the surface temperature. Conclusions. We conclude that XMMU J173203.3−344518 in the remnant HESS J1731−347 fits into a strange star scenario that is also consistent with heavier compact stars, which can also belong to the same class and constitute an homogeneous type of self-bound objects produced in Nature.

The distribution of masses for neutron stars is analysed using the Bayesian statistical inference, evaluating the likelihood of the proposed Gaussian