What Is a Neutron Star, and Why Do They Matter?  Imagine holding a teaspoon that weighs more than every skyscraper on Earth combined. Neutron stars are cosmic heavyweights, dense beyond anything we know and filled with mysteries at the frontier of physics. From Supernova to Neutron Star: How Extreme Matter Is Born  When a massive star, roughly 8 or more times the Sun’s mass, exhausts its fuel, it can undergo core collapse. Depending on details such as metallicity and mass loss, many such stars explode as supernovae and leave neutron stars behind. The star erupts in a spectacular supernova, blasting its outer layers into space and crushing its core into an ultra‑dense remnant of neutrons. Under this incredible pressure, electrons and protons merge through a process called electron capture. What remains is an ultra‑compact sphere made primarily of neutrons, with small fractions of protons, electrons, and possibly more exotic particles such as muons or hyperons in its interior. O...