Neutron-star radii provide useful information on the equation of state of
neutron rich matter. Particularly interesting is the density dependence of the
equation of state (EOS). For example, the softening of the EOS at high density,
where the pressure rises slower than anticipated, could signal a transition to
an exotic phase. However, extracting the density dependence of the EOS requires
measuring the radii of neutron stars for a broad range of masses. A ``normal''
1.4 solar mass neutron star has a central density of a few times nuclear-matter
saturation density. In contrast, low mass (of the order of 0.5 solar masses)
neutron stars have central densities near nuclear-matter saturation density so
its radius provides information on the EOS at low density. Unfortunately,
low-mass stars are rare because they may be hard to form. Instead, a precision
measurement of nuclear radii on atomic nuclei may contain similar information.
Indeed, we find a strong correlation between the neutron radius of 208Pb and
the radius of a 0.5 solar-mass neutron star. Thus, the radius of such a neutron
star can be inferred from a measurement of the the neutron radius of 208Pb.
Comparing this value to the measured radius of a 1.4 solar-mass neutron star
should provide the strongest constraint to date on the density dependence of
the equation of state.Comment: 9 pages and 5 eps. figures (included