Quark Stars

Quark stars are what you might get if a collapsing star were to proceed beyond the neutron-star condition in which the star's constituents are chiefly neutrons (each neutron is itself a sovereign parcel consisting, in the main, of two down quarks and one up quark) all the way to a condition in which the very neutron membranes would be dissolved, allowing the quarks to run together. Brookhaven's RHIC collider attempts to do something like this on a much smaller scale when it smashes together two gold atoms.

In the case of a quark star it is immutable self-gravity rather than manmade accelerator gradients that provide the needed crushing power. Under these conditions it might be energetically feasible for many quarks to exist as strange quarks rather than the lighter up and down quarks. Hence the name "strange stars."

Evidence for quark stars comes now in the form of observations of two neutron stars, viewed at x-ray wavelengths by the Chandra x-ray telescope and in the visible by the Hubble Space Telescope.

One of the objects, RXJ1856, is too small (to judge by its wealth of x ray and dearth of visible emissions) to be a conventional neutron star made primarily of neutrons. The other object, 3C58, seems to have cooled too quickly (to judge by its present measured warmth and its known lifetime, drawing upon medieval Chinese records of the object's birth as a supernova in 1181 CE) to be an ordinary neutron star.

In both cases the observations tally better with a star of quarks (one big nucleus), or a mix of quark and neutron layers. (Two articles to appear in Astrophysical Journal; 3C48 preprint, Slane et al., astro-ph/0204151; RXJ1856 preprint, Drake et al., astro-ph/0204159).

A day after the press conference at which these results were announced, a new preprint (astro-ph/0204199) appeared which suggests that the distance to JXJ1856 is actually further away than the earlier estimate and that the object need not be a quark star after all.