A neutron star can pack more mass than our entire Sun into a sphere only about 20 kilometres across — roughly the size of a city — and a teaspoon of its material would weigh about a billion tonnes on

A neutron star is one of the few objects in astronomy where the familiar scale of a city and the unfamiliar scale of nuclear physics meet in the same sentence. NASA’s Imagine the Universe site describes a neutron star as the collapsed core left behin... [6413 chars]