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

Abstract

Once further confirmed in future analyses, the radius and mass measurement of HESS J1731-347 with M = 0.77 − 0.17 + 0.20 M ⊙ and R = 10.4 − 0.78 + 0.86 km will be among the lightest and smallest compact objects ever detected. This raises many questions about its nature and opens up the window for different theories to explain such a measurement. In this article, we use the information from Doroshenko et al. on the mass, radius, and surface temperature together with the multimessenger observations of neutron stars to investigate the possibility that HESS J1731-347 is one of the lightest observed neutron star, a strange quark star, a hybrid star with an early deconfinement phase transition, or a dark matter–admixed neutron star. The nucleonic and quark matter are modeled within realistic equation of states (EOSs) with a self-consistent calculation of the pairing gaps in quark matter. By performing the joint analysis of the thermal evolution and mass–radius constraint, we find evidence that within a 1σ confidence level, HESS J1731-347 is consistent with the neutron star scenario with the soft EOS as well as with a strange and hybrid star with the early deconfinement phase transition with a strong quark pairing and neutron star admixed with dark matter.

Ultracompact hybrid stars consistent with multimessenger astrophysics

“…The alternative value c 2 s = 2/3 is intermediate between the maximally stiff and the asymptotic high-density value c 2 s = 1/3 corresponding to a conformally symmetric quark phase. Other values of c 2 s have been considered very recently by several authors (Brodie & Haber 2023;Sagun et al 2023) in the context of HESS J1731-347 for al-ternate nucleonic EoSs.…”

Two-flavor Color Superconducting Quark Stars May Not Exist

“…We mention here that there are several alternative models discussed in the literature for HESS J1731-347, such as (hybrid) neutron stars (Brodie & Haber 2023;Huang et al 2024;Kubis et al 2023;Laskos-Patkos et al 2024;Li & Sedrakian 2023;Tsaloukidis et al 2023), and dark-matteradmixed neutron stars (Routaray et al 2023;Sagun et al 2023). In practice, measuring the mass and radius of compact stars is an extremely challenging task (see further discussions in, e.g., Brandes et al 2023;Jiang et al 2023;.…”

Pair Creation in Hot Electrosphere of Compact Astrophysical Objects

“…Recent study of quark stars has focused on their evolution within full general relativity (Zhou et al 2021;Zhu & Rezzolla 2021), their cooling (Zapata et al 2022), finite temperature effects (Chu et al 2019(Chu et al , 2021, strong rotation (Sun & Huang 2022) and differential rotation (Szkudlarek et al 2019), effects from the presence of magnetic field (Terrero et al 2021), limits on possible electric charge (Gonçalves & Lazzari 2020;Estevez-Delgado & Estevez-Delgado 2022), and the effects of modified gravity (Deb et al 2019). Constraints from gravitational waves observations on strange stars were discussed in Mannarelli & Tonelli (2018) and Cao et al (2022), and the onstraints on the mass-radius relationship in observations of the compact object HESS J1731-347 were established in Oikonomou & Moustakidis (2023), Rather et al (2023), andSagun et al (2023).…”