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 Earth, more than every human being alive combined.

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 Earth, more than every human being alive combined.

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 behind when a massive star runs out of fuel and its centre falls inward. The result can contain about the mass of the Sun in a sphere only about 20 kilometres across. That is a diameter comparable to a la…