Neutron-degenerate matter is a type of dense matter primarily found in the cores of neutron stars. It consists mostly of neutrons, which are subatomic particles that have no electric charge. This state of matter occurs when the gravitational pressure is so intense that electrons and protons combine to form neutrons, resulting in a highly compact structure. In neutron-degenerate matter, the neutrons are packed closely together, creating a strong repulsive force due to the principles of quantum mechanics. This prevents further collapse under gravity, allowing neutron stars to exist in a stable state. The study of neutron-degenerate matter helps scientists understand the life cycles of stars and the fundamental forces of nature.