Mubasher Jamil and Farook Rahaman investigated the effects of the accretion of phantom (dark) energy with non-zero bulk viscosity onto a Morris-Thorne wormhole. They found that if the bulk viscosity is large then the mass of wormhole increases rapidly as compared to small or zero bulk viscosity.
Exotic tunnel like topology in spacetime commonly called wormhole arises as a solution to the Einstein field equations. A typical two mouth wormhole joins two arbitrary points either of the same spacetime or two different spacetimes. Morris and Thorne suggested the existence of exotic matter for the stability of a wormhole. The stress energy tensor Tµν of the exotic matter must violate the Null energy condition (Tµν× u^µ × u^ν ≥ 0) where u^µ is the future directed null vector. They concluded that an advanced civilization can produce a wormhole for interstellar travel by injecting sufficient amount of exotic matter in it. Recent interest in wormhole has arose due to the discovery of exotic phantom energy driving the accelerated expansion of the universe. It has been proposed that wormhole can be stabilized by the accretion of phantom energy and it can result in increasing the size of the wormhole to engulf the observable universe.
Jamil and colleagues considered a similar scenario where they incorporated the effects of bulk viscous stress in their calculations. The bulk viscosity is quite relevant in physical cosmology as it can cause expansion of the universe due to its negative pressure. The presence of viscous fluid can also explain the observed high entropy per baryon ratio in the universe.
In their paper, they presented the relativistic model of accretion of viscous phantom energy onto a stationary wormhole. Later they considered and studied the evolution of mass of wormhole (WH) in two special cases of bulk viscosity in their model: (a) the constant viscosity; and (b) the power law viscosity.
In our model, we have incorporated the viscous pressure along the usual isotropic pressure in the accretion model. Our model predicts the growth of wormholes by the accretion of bulk viscous phantom energy. For large bulk viscosity, the increase in the mass of wormhole is large as compared to small viscosity.— said Mubasher Jamil, lead author of the study.
And what they found is given below:
(1) For constant bulk viscosity, they found that the mass of the wormhole increases under the assumption of large viscosity. Hence the wormhole is perfectly supported with the viscous phantom energy.
(2) For power law viscosity, their model predicted the growth of the wormhole if the dominant energy condition (ρ + p > 0) is violated.
Reference: Mubasher Jamil, Rahaman Farook, “Wormholes in Bulk Viscous Cosmology”, Astronomical Journal, pp. 1-5, 2008. https://arxiv.org/abs/0806.1319
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