Hybrid stars that masquerade as neutron stars

We show that a hybrid ( nuclear+ quark matter) star can have a mass- radius relationship very similar to that predicted for a star made of purely nucleonic matter. We show this for a generic parameterization of the quark matter equation of state and also for an MIT bag model, each including a phenomenological correction based on gluonic corrections to the equation of state. We obtain hybrid stars as heavy as 2 M(circle dot) for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal and coworkers using many- body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.