  It has been recently suggested that differences in the charge radii of mirror
nuclei are proportional to the neutron-skin thickness of neutron-rich nuclei
and to the slope of the symmetry energy $L$ [B.A. Brown Phys. Rev. Lett. 119,
122502 (2017)]. The determination of the neutron skin has important
implications for nuclear physics and astrophysics. Although the use of
electroweak probes provides a largely model-independent determination of the
neutron skin, the experimental challenges are enormous. Thus, the possibility
that differences in the charge radii of mirror nuclei may be used as a
surrogate for the neutron skin is a welcome alternative. To test the validity
of this assumption we perform calculations based on a set of relativistic
energy density functionals that span a wide region of values of $L$. Our
results confirm that the difference in charge radii of various
neutron-deficient nickel isotopes and their corresponding mirror nuclei is
indeed strongly correlated to both the neutron-skin thickness and $L$.
Moreover, given that various neutron-star properties are also sensitive to $L$,
a data-to-data relation emerges between the difference in charge radii of
mirror nuclei and the radius of low-mass neutron stars.

Nuclear Theory;Solar and Stellar Astrophysics;Nuclear Experiment