Neutron star
The conditions in neutron stars are very different from those encountered on Earth, as a result of the high density and gravity of neutron stars; their masses are of order the mass of a star, but they have sizes around in radius, which is comparable to the size of the center of large cities such as London. Neutron stars also have the property that as they become more massive, their diameter decreases. The mass of PSR J1614–2230 is the second highest of all the known neutron stars. The existence of a neutron star with such a high mass constrains the composition and structure of neutron stars, both of which are poorly understood. The reason for this is that the maximum mass of a neutron star is dependent upon its composition. A neutron star composed of matter such as hyperons or kaon condensates would collapse to form a black hole before it could reach the observed mass of PSR J1614–2230, meaning neutron star models that include such matter are strongly constrained by this result.