Extragalactic Astronomy

This book deals with some theoretical features of wormholes and gravastars. In chapter one, we have discussed the definition of wormholes and gravastars and also the works in the spheres by various distinguished authors. In chapter two, we discuss on wormholes supported by two non interacting fluids. The exact wormhole solutions are found in the model having, besides real matter, an anisotropic dark energy. We have shown that the exotic matters that are the necessary ingredients for wormhole physics violate null and weak energy conditions (NEC and WEC) but obey strong energy conditions (SEC) marginally. We have calculated the effective mass of the wormhole up to 4 km throat radius as 0.561 times a Solar Mass, and total gravitational energy of the wormhole as 1.9397 and shown that there is a repulsion around the throat which is much expected for valid construction of a wormhole. In chapter three we search for higher dimensional wormholes with non commutative geometry. It is known that noncommutativity geometry, an offshoot of string theory, replaces point-like structures with smeared objects.