Neutron stars pack more than a Sun’s mass into a sphere 20–26 kilometers across

A science post explains that neutron stars form when massive stars collapse, compressing more than a Sun’s worth of mass into a sphere 20–26 kilometers across. Their outer cores are expected to contain superfluid neutrons, while their inner cores may hold exotic forms of matter. The post describes their extreme density as a way to study conditions that cannot be reproduced on Earth.