A typical neutron star has a mass between 1.35 and about 2.1
solar masses, with a corresponding radius of about 12 km if the
Akmal-Pandharipande-Ravenhall (APR) Equation of state is used.
In contrast, the Sun's radius is about 600,000 times larger.
Neutron stars have overall densities predicted by EOS APR of 3.7
(2.6 times Solar density) to 5.9 kg/m³ (4.1 times Solar
density), which compares with the approximate density of an
atomic nucleus of 3 kg/m³. The neutron star's density varies
from below 1 kg/m³ in the crust increasing with depth to above 6
or 8 kg/m³ deeper inside. In general, compact stars of less than
1.44 solar masses, the Chandrasekhar limit, are white dwarfs;
above 2 to 3 solar masses (the Tolman-Oppenheimer-Volkoff
limit), a quark star might be created, however this is
uncertain. Gravitational collapse will always occur on any star
over 5 solar masses, inevitably producing a black hole. The
gravitational field at the star's surface is about 2times
stronger than on Earth. The escape velocity is