Sun’s mass squeezed into a city-sized neutron star

Neutron stars cram roughly 1–2 solar masses into a sphere about 20 km across; a sugar-cube of their matter would weigh around a billion tonnes on Earth. This extreme density pushes matter to nuclear scales, making neutron stars natural laboratories for ultra-dense matter and helping constrain the equation of state, with many such stars acting as pulsars or magnetars.