Strangelet Searches from Neutron Stars, Binary Mergers, and Gamma-Ray Bursts with Current and Future Observatories

TL;DR

The paper investigates the existence and detectability of strangelets, stable clusters of strange quark matter, by integrating dense QCD theory with multimessenger astrophysical data. It builds a framework around the 2SC-to-CFL phase transition in dense quark matter to estimate production cross-sections and interaction rates, linking microscopic parameters to macroscopic observables. Using archival gamma-ray data from H.E.S.S., Fermi-LAT, and MAGIC-II, the study constrains monochromatic gamma-ray line signatures and projects the sensitivity of the CTA to such lines in diverse environments, notably HESS J1731-347, GW170817, and GRB 250702B. The work highlights how upcoming observations, coupled with robust statistical pipelines and cross-instrument formats, can either reveal or tightly constrain SQM phenomenology, potentially reshaping our understanding of compact objects and the role of exotic matter in the cosmos.

Abstract

Strange quark matter (SQM) is considered a possible true ground state of QCD at high densities. This idea motivates research on exotic compact objects and certain cosmic-ray phenomena. For instance, the remnant HESS J1731-347 contains a low-mass neutron star, about $0.77^{+0.20}_{-0.17}$ $M_\odot$ and $10.4^{+0.86}_{-0.78}$ km in radius, making it a strong candidate for a strange quark star. Other events, such as GW170817 and GRB 250702B, provide conditions that may favor the formation of strangelets. Strangelets are stable clusters of SQM, potentially created during the phase transition between the 2SC and CFL color-superconducting states. These clusters could generate monochromatic $γ$-ray lines in very-high-energy spectra through self-annihilation. This work analyzes the stability of strangelets, production cross-sections, and mass-to-charge ratios using QCD-based models. Data from H.E.S.S., Fermi-LAT, MAGIC-II, and CTA were used to set limits on spectral features and possible fluxes. Detecting narrow $γ$-ray lines will require improved instrument sensitivity. By integrating evidence from multimessenger astrophysics and dense QCD simulations, this study investigates the equations of state for compact stars and explores the potential cosmological influence of SQM.

Figures (4)

• Figure 1: Strangelet production rates in HESS J1731-347 for baseline, optimistic, and conservative scenarios, showing the rate $\dot{N}$ (s$^{-1}$) versus the baryon number $A$, with a secondary axis for radius $\approx 0.7\times A^{1/3}$ in fm Farhi1984.
• Figure 2: Constrained regions from Fermi-LAT, HESS (2011 and 2018), and projected sensitivities for CTA and MAGIC-II as a function of $\log_{10} A$ vs. $\log_{10} f_\gamma$. Results are presented for the Hadronic and Hybrid models at $\varepsilon = 100$ MeV and 1.0 GeV, respectively, with mass parameter contours given by $\log_{10}(M_0/M_{\odot})$.
• Figure 3: Constrained regions from Fermi-LAT, HESS (2011 and 2018), and projected sensitivities for CTA and MAGIC-II as a function of $\log_{10} A$ vs. $\log_{10} f_\gamma$. The results for the Hadronic and Hybrid models at $\varepsilon = 100$ MeV and $1.0$ GeV, respectively, with production rate contours given by $\log_{10}(\dot N$ (s$^{-1}))$.
• Figure 4: Summary of $\gamma$-ray constraints from Figures \ref{['fig:constraintsmass']} and \ref{['fig:constraintsrate']} on strangelet parameters for HESS J1731-347. The plot shows the constrained regions from Fermi-LAT, HESS (2011 and 2018), and projected sensitivities for CTA and MAGIC-II in the $\log_{10} A$ vs. $\log_{10} f_\gamma$ plane.