Massive neutron stars have sizable quark-matter cores, according to a study published in the journal Nature Physics. An artist’s conception of a massive neutron star. Image credit: L. Calçada / ESO. Neutron stars, which are the result of a supernova explosion, are the smallest and densest stars in the Universe. While these objects typically have a radius of about 10 km, they average between 1.4 and 2.2 solar masses. Inside neutron stars, atomic...