Gravitational Merging as a Possible Source for the Cosmological Accelerating

Gravitational merging (or clustering) of cosmic objects is regarded as a possible source of the extra-acceleration of the universe at large scale. The merging/clustering of cosmic objects introduces a correction term in the equation of state for the effective present cosmic fluid in the form of $P=w\rho+b\rho^2$. As a result, an alternative relation for the energy density includes over and under-dense regions is obtained that coincide with the conventional relation in the standard limit. By analogy with bubbles, the under-dense regions (voids) in the cosmic fluid is shown to provide the needed negative pressure. Invoking the observational constraint for the dark energy equation of state $w$, we show that the merging of voids will act as a possible source of extra-accelerating at large scale in comparison with non-merging cosmic gas.