The Neutron star Interior Composition Explorer (NICER) mission will study neutron stars, the densest known objects in the cosmos. These neutron star animations and graphics highlight some of their unique characteristics.
A neutron star begins its life as a star between about 7 and 20 times the mass of the sun. When this type of star runs out of fuel, it collapses under its own weight, crushing its core and triggering a supernova explosion. What remains is an ultra-dense sphere only about the size of a city across, but with up to twice the mass of the sun squeezed inside.
This animation shows the size and scale of a neutron star over San Fransisco.
Neutron stars squeeze up to two solar masses into a city-size volume, giving rise to the highest stable densities known anywhere. The nature of matter under these conditions is a decades-old unsolved problem.