Figure 1

The central energy density and mass of maximum mass configurations. Symbols reflect the nature of the EOS selected from Ref. 18. NR are nonrelativistic potential models, R are field-theoretical models, and exotica refers to NR or R models in which strong softening occurs, due to the occurrence of hyperons, a Bose condensate, or quark matter. The exotica points include self-bound strange quark matter stars. For comparison, the central density–maximum mass relations for the redshift, Tolman VII ($w=0$), and Tolman IV ($N=2$) bounds from Eqs. (4, 6, 11) are shown. The dashed lines for $1.44M_{\odot }$ and $2.2M_{\odot }$ serve to guide the eye.Reuse & Permissions

Figure 2

Measured and estimated masses of neutron stars in radio binary pulsars and in x-ray accreting binaries. Sources are listed by letter (Refs. [20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36]). Error bars are $1\sigma$. Vertical dotted lines show average masses of each group ($1.62M_{\odot }$, $1.33M_{\odot }$, and $1.56M_{\odot }$); dashed vertical lines indicate inverse error weighted average masses ($1.48M_{\odot }$, $1.41M_{\odot }$, and $1.34M_{\odot }$).Reuse & Permissions