The strange quark matter hypothesis suggests that deconfined quark matter composed of about equal fractions of up, down and strange quarks could be the true ground state of matter. This will be true if the ground state of strange quark matter (SQM) has a lower energy per baryon than normal nuclear matter, making it absolutely stable.
The SQM hypothesis is of fundamental importance with regard to neutron star structure. If a "seed" of SQM appears in the core of a neutron star it will proceed to consume the surrounding neutrons, which would lead to a burning (exothermal) conversion of the entire star, deconfining the baryon matter into SQM. The end product of this conversion will be a compact object composed almost entirely of SQM, which has been referred to as a "Strange Quark Star" . The timescale for such a burning has been estimated to be of the order of minutes . Thus, the SQM hypothesis predicts that some (and maybe all) neutron stars could actually be strange quark stars.
Various processes have been suggested for creating SQM seeds in neutron stars [3], and can be divided into two distinct sources:
?? The absorption of an external source SQM "nugget" formed elsewhere (for example, from debris of a strange star which has coalesced with a binary counterpart). However, a quantitative estimate of the flux of SQM in the universe is dependent on many assumptions, and thus it is impossible to constrain the flux (various arguments can be made for evolutionary selection effects).
?? A SQM seed could form as an internal source in the core of a neutron star should deconfinement become favorable. The availability of internal sources clearly depends only on the structure of the neutron star. Furthermore, assuming the SQM hypothesis is correct, if some internal source is available in all neutron stars, then all existing neutron stars must actually be strange quark stars.