<P> Degenerate matter includes the part of the universe that is made up of neutron stars and white dwarfs . </P> <P> Strange matter is a particular form of quark matter, usually thought of as a liquid of up, down, and strange quarks . It is contrasted with nuclear matter, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks . At high enough density, strange matter is expected to be color superconducting . Strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars). </P> <P> In particle physics and astrophysics, the term is used in two ways, one broader and the other more specific . </P> <Ol> <Li> The broader meaning is just quark matter that contains three flavors of quarks: up, down, and strange . In this definition, there is a critical pressure and an associated critical density, and when nuclear matter (made of protons and neutrons) is compressed beyond this density, the protons and neutrons dissociate into quarks, yielding quark matter (probably strange matter). </Li> <Li> The narrower meaning is quark matter that is more stable than nuclear matter . The idea that this could happen is the "strange matter hypothesis" of Bodmer and Witten . In this definition, the critical pressure is zero: the true ground state of matter is always quark matter . The nuclei that we see in the matter around us, which are droplets of nuclear matter, are actually metastable, and given enough time (or the right external stimulus) would decay into droplets of strange matter, i.e. strangelets . </Li> </Ol>

Who studies matter and energy and how they interact