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-p and Lambda-d correlation data from the LHC and RHIC and hypernuclear spectroscopy that fix the Lambda-NN force, combined with quantum Monte Carlo calculations of hyperonic matter.
Status in the literature
Unverified note
Repulsive Lambda-NN forces fitted to hypernuclei can suppress hyperons (Lonardoni et al., 2015), but the three-body force remained poorly constrained as of 2026.
Related problems
- More general than Density dependence of the $\Lambda$ potential in nuclear matter