Oppenheimer
Oppenheimer and Serber quickly realized that, if the Sun has a neutron core at its center, and if the core’s mass is a large fraction of the Sun’s mass, then the core’s intense gravity will hold the Sun’s outer layers in a tight grip, making the Sun’s circumference far smaller than it actually is. Thus, Landau’s neutron-core idea could work only if neutron cores can be far less massive than the Sun.