Twin stars, i.e., pairs of compact stars with identical masses but distinct radii, have long been considered a potential signature of a phase transition in dense QCD matter. Using a model-agnostic equation-of-state (EOS) inference setup, we show that once constraints from chiral effective field theory, perturbative QCD, and current multimessenger observations are simultaneously imposed, such solutions are strongly suppressed. The remaining viable EOSs occupy two highly fine-tuned regions in parameter space, characterized by either a discontinuous early onset phase transition or a rapid crossover at higher density, the latter coupled with a distinctive double-peaked speed of sound. Given that neither class features a conformalization of the EOS upon entering the second branch, we argue that the standard twin-star scenario linking the mass-radius discontinuity to deconfinement can be effectively ruled out.

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• Equations of state of nuclear matter
• Nuclear astrophysics
• Nuclear matter in neutron stars
• Quantum chromodynamics
• Quark matter
• Neutron stars & pulsars