8
M. C. Miller
Fig. 1.2 Mass versus radius for nonrotating stars constructed using several different high-density
equations of state. Rotation changes the radius to second order in the spin rate, but the corrections
are minor for known neutron stars. The solid curves include only nucleonic degrees of freedom
(these are the mass-radius relations for the soft, medium, and hard equations of state from [100]),
the short dashed lines assume bare strange matter [121], and the dotted curve uses a hybrid quark
equation of state with a phase transition [34]. The horizontal dashed line at 1.2 M represents
approximately the minimum gravitational mass for a neutron star in current formation scenarios,
whereas the horizontal dashed line at 2.01 M shows the highest precisely measured gravitational
mass for a neutron star
include hyperons or deconfined quarks. We plot some mass-radius relations from
representative equations of state in Fig. 1.2. It is clear that models can be constrained
tightly if more massive neutron stars are discovered, or if neutron star radii can be
measured with accuracy and precision (especially for stars of known mass).
Constraints on the equation of state of cold dense matter can be obtained from
astronomical observations or laboratory experiments. Some of the more useful
experimental data come from relativistic heavy-ion collisions, which can reach 2
to 4.5 times nuclear saturation density [70] but which have relativistic temperatures
and are therefore not degenerate. In addition, in such collisions the time for weak
interactions to occur is short, in contrast to the effectively infinite time available
in neutron stars. Laboratory data also include the binding energies of light nuclei
and recent measurements of the neutron skin thickness of heavy nuclei such as
208 Pb (0.33
+0.16
−0.18 fm according to the PREX team [3]; see [178] for some of the
implications of the expected more precise future measurements), which provide
a rare glimpse of neutron-rich matter because the neutron wavefunctions extend
slightly beyond the proton wavefunctions. These experiments thus measure the
microphysics semi-directly, whereas all astrophysical observations place indirect
constraints. In order to make explicit contact between microphysics and astrophysics
we now discuss briefly how to construct models of neutron stars given a high-density
equation of state.
M. C. Miller
Fig. 1.2 Mass versus radius for nonrotating stars constructed using several different high-density
equations of state. Rotation changes the radius to second order in the spin rate, but the corrections
are minor for known neutron stars. The solid curves include only nucleonic degrees of freedom
(these are the mass-radius relations for the soft, medium, and hard equations of state from [100]),
the short dashed lines assume bare strange matter [121], and the dotted curve uses a hybrid quark
equation of state with a phase transition [34]. The horizontal dashed line at 1.2 M represents
approximately the minimum gravitational mass for a neutron star in current formation scenarios,
whereas the horizontal dashed line at 2.01 M shows the highest precisely measured gravitational
mass for a neutron star
include hyperons or deconfined quarks. We plot some mass-radius relations from
representative equations of state in Fig. 1.2. It is clear that models can be constrained
tightly if more massive neutron stars are discovered, or if neutron star radii can be
measured with accuracy and precision (especially for stars of known mass).
Constraints on the equation of state of cold dense matter can be obtained from
astronomical observations or laboratory experiments. Some of the more useful
experimental data come from relativistic heavy-ion collisions, which can reach 2
to 4.5 times nuclear saturation density [70] but which have relativistic temperatures
and are therefore not degenerate. In addition, in such collisions the time for weak
interactions to occur is short, in contrast to the effectively infinite time available
in neutron stars. Laboratory data also include the binding energies of light nuclei
and recent measurements of the neutron skin thickness of heavy nuclei such as
208 Pb (0.33
+0.16
−0.18 fm according to the PREX team [3]; see [178] for some of the
implications of the expected more precise future measurements), which provide
a rare glimpse of neutron-rich matter because the neutron wavefunctions extend
slightly beyond the proton wavefunctions. These experiments thus measure the
microphysics semi-directly, whereas all astrophysical observations place indirect
constraints. In order to make explicit contact between microphysics and astrophysics
we now discuss briefly how to construct models of neutron stars given a high-density
equation of state.