Presence of exotic matter in the Cooperstock and Tieu galaxy model
  We analyze the presence of an additional singular thin disk in the recent General Relativistic model of galactic gravitational field proposed by Cooperstock and Tieu. The physical variables of the disk's energy-momentum tensor are calculated. We show that the disk is made of exotic matter, either cosmic strings or struts with negative energy density. 
D. Vogt and P. S. Letelier