A light strange star in the remnant HESS J1731−347: Minimal consistency checks

Abstract

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.

Strange Quark Stars: The Role of Excluded Volume Effects

“…Another interesting aspect is that models incorporating the excluded volume effect naturally satisfy observations of the recently observed object by HESS [46]. This object is uniquely characterized by its very small mass and radius, which challenges theoretical models of objects containing hadronic matter [56]. As shown in Figure 5, models of strange quark matter agree more naturally with the observation of HESSJ1731.…”

What Is the Nature of the HESS J1731-347 Compact Object?

“…It was proposed that HESS J1731-347 could be a candidate for a strange quark star (QS) comprising all existing massradius measurements of CSs (Di Clemente et al 2022;Das & Lopes 2023;Horvath et al 2023). However, unpaired quark matter undergoes fast cooling, leading to difficulties in reproducing the surface temperature, presented by Doroshenko et al (2022).…”

Two-flavor Color Superconducting Quark Stars May Not Exist

“…Along this line, the CFL quark stars have been studied within MIT bag models in light of the compact object in HESS J1731-347. Horvath et al (2023) showed that candidate XMMU J173203.3-344518 might fit into a strange star scenario that could also be consistent with heavier compact stars using the same quark EOS in the MIT bag model, and discussed a possible scenario where a small gap (Δ 1 MeV) in the CFL phase would explain the high surface temperature of XMMU J173203.3-344518. Oikonomou & Moustakidis (2023) indicated that the parameter space could be further confined to the additional requirement for a high maximum mass (M TOV 2.6 M e ; Abbott et al 2020) without violating the conformal bound (Fujimoto et al 2022).…”