Why are big neutron stars like Tootsie Pops?
New instruments can generate maps of neutron stars in unprecedented detail, but physicists are still trying to figure out what lies beneath the surface. (NASA, NICER, GSFC's CI Lab/)The Earth is a balmy oasis in cosmos of raging extremes, and few bodies are more extreme than neutron stars. These objects form when stars of a certain mass die, and their cores collapse and cram a couple of suns worth of mass into an orb the size of a city. Inside, atoms as we know them—dense beads of protons and neutrons surrounded by airy clouds of electrons—cease to exist. Gravity crushes the atomic centers together and neutrons stand shoulder to shoulder. Add much more mass and the star would collapse into a black hole, its atoms vanishing from view. “Neutron stars,” writes Jocelyn Read, an astrophysicist at California State University, Fullerton are “the place where matter makes its last stand against...