How do hyperons fit inside two-solar-mass neutron stars?

In plain words

At high density it becomes energetically favorable to turn some neutrons into hyperons (baryons containing a strange quark), which softens the matter so much that most models cannot then support stars of two solar masses. Yet such stars are observed.

Precise statement

With hyperon-nucleon (YN) and hyperon-nucleon-nucleon (YNN) forces constrained by hypernuclear binding energies, femtoscopic correlations and lattice QCD, determine the density at which $\Lambda$ and $\Sigma-$ hyperons appear and whether $M_{\mathrm{TOV}} \ge 2\ \text{solar masses}$ survives. Answer: the mechanism (repulsive YNN forces, early quark deconfinement, or absence of hyperons) and the interaction parameters that produce it.

What would settle it

Femtoscopic $\Lambda-\mathrm{p}$ and $\Lambda-\mathrm{d}$ correlation data from the LHC and RHIC and hypernuclear spectroscopy that fix the $\Lambda-\mathrm{NN}$ force, combined with quantum Monte Carlo calculations of hyperonic matter.

Status in the literature

Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.

Repulsive $\Lambda-\mathrm{NN}$ forces fitted to hypernuclei can suppress hyperons (Lonardoni et al., 2015), but the three-body force remained poorly constrained as of 2026.

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