Inside a Neutron Star: Matter May Not Exist as We Know It

A neutron star can contain more mass than the Sun inside an object only tens of kilometers across. We understand its outer layers reasonably well. But travel deeper, toward pressures and densities impossible to reproduce directly in laboratories, and certainty begins to disappear. Do neutrons remain recognizable particles? Do new particles emerge? Can matter transform into a state containing deconfined quarks? Astronomers are now using X rays and gravitational waves to investigate one of the strangest laboratories in the universe.