Does the sound speed exceed the conformal bound inside neutron stars?
In plain words
In matter made of free quarks at very high density, sound travels at the speed of light divided by the square root of 3. Neutron-star data suggest sound travels faster than this somewhere inside, but the evidence depends on modeling assumptions.
Precise statement
Determine whether $c_s^{2} = \mathrm{d}P/\mathrm{d}\epsilon$ exceeds $c^2/3$ (the value for free massless quarks) at some density below the central density of a maximum-mass star. Answer: yes or no, with posterior probability given pulsar masses, NICER radii, tidal deformabilities, chiral EFT below about $2 n_0$ and perturbative QCD limits.
What would settle it
Equation-of-state inference using 2 percent radius measurements across masses from 1.2 to 2.1 solar masses.
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.
Bayesian analyses including two-solar-mass pulsars and NICER radii have found $c_{s}^{2} > c^{2}/3$ in most posteriors since about 2018, with the probability depending on the priors as of 2026.
Problems built on this one
Special cases
Results
No results have been posted on this problem yet.
Post a result · how results are checked
Sign in to follow or save this problem
Comments (0)
Comments are not records: they are not signed, stamped or logged. How comments work
No comments yet.
Sign in to comment.