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We explore a class of compact charged spheres made of a charged perfect fluidwith a polytropic equation of state. The charge density is chosen to beproportional to the energy density. The study is performed by solving theTolman-Oppenheimer-Volkoff (TOV) equation which describes the hydrostaticequilibrium. We show the dependence of the structure of the spheres for severalcharacteristic values of the polytropic exponent and for different values ofthe charge densities. We also study other physical properties of the chargedspheres, such as the total mass, total charge, radius and sound speed and theirdependence on the polytropic exponent. We find that for the polytropic exponent\gamma=4/3 the Chandrasekhar mass limit coincides with the Oppenheimer-Volkoffmass limit. We test the Oppenheimer-Volkoff limit for such compact objects. Wealso analyze the Buchdahl limit for these charged polytropic spheres, whichhappens in the limit of very high polytropic exponents, i.e., for a stiffequation of state. It is found that this limit is extremal and it is aquasiblack hole.

Polytropic spheres with electric charge: compact stars, the Oppenheimer-Volkoff and Buchdahl limits, and quasiblack holes