  We consider the linear equation of state for matter distributions that may be
applied to strange stars with quark matter. In our general approach the compact
relativistic body allows for anisotropic pressures in the presence of the
electromagnetic field. New exact solutions are found to the Einstein-Maxwell
system. A particular case is shown to be regular at the stellar centre. In the
isotropic limit we regain the general relativistic isothermal universe. We show
that the mass corresponds to values obtained previously for quark stars when
anisotropy and charge are present.
