International Astronomy and Astrophysics Research Journal

We use both analytical methods and statistical methods to show that certain physical processes (such as jet internal pressure and luminosity) which occur in radio galaxies may be propelled by both the source central engine and dark/vacuum energy. We do this by carrying out linear regression analysis of observed source linear sizes (D) of the more extended radio galaxies against their corresponding observed redshifts (z) in our sample. In addition to that, we carry out similar analysis on the observed linear sizes of compact steep spectrum (CSS) galaxies against their corresponding observed redshifts. Results of these regressions indicate that if we take D to be distance between any two positions in the environment in which the source is domiciled, then cosmic evolution relates inversely with the distance between the two positions in question – it is given by (1+z)~D^-J (where the index is different for both sources) for both the more extended EGR galaxies and CSS radio galaxies. Since “a higher redshift implies an earlier epoch”, and redshift has a direct relationship with expansion velocity between any two points in space, the results of the analyses simply suggest that at earlier epoch, the expansion rate of the universe is higher. Our results also indicate that the effect of cosmic evolution in the extended EGR galaxies is more than the effect in the CSS radio galaxies (i.e.D_z(EGRg) > D_z(CSSg)) . Since the source components (jets and lobes) of the more extended EGR galaxies are located in the intergalactic media (IGM), while the components of the CSS radio galaxies are domiciled within their individual host galaxies (i.e. the interstellar media [ISM]), the result (D_z(EGRg) > D_z(CSSg)) can be interpreted to mean that cosmic evolution shows greater effect in the IGM (i.e. more rarefied medium) than in the ISM (i.e. less rarefied medium). Hence, from the results of the analyses, we may state that if dark can be interpreted to mean that cosmic evolution shows greater effect in the IGM (i.e. more rarefied medium) than in the ISM (i.e. less rarefied medium). Hence, from the results of the analyses, we may state that if dark energy is defined as the intrinsic tendency of vacuum (or free space) to increase in volume, then the inconsistency in  D_z(EGRg)  and  D_z(CSSg)  is simply a manifestation of dark energy. Therefore, we may state that dark energy is a forcing function behind cosmic evolution. Finally, using semi-empirical relations, we find that generally evolution of radio galaxies (which manifests in jet internal pressure and luminosity) derives from two main factors; namely, the power of central engine (which presumably harbours super massive blackhole) and dark energy according to the relation, \(\frac{p^{0.06}}{p_{j}^{15.6}}= R (\frac{1}{m_{h}c^{3}\Omega \epsilon})^{0.06} \frac{(1+z)^{0.12}}{\mathcal{P}_{\mathcal{CE}[z(EGRg]}}\) where P_CE[z(EGRg)] is power of the central engine of extended radio galaxy, P_j jet internal pressure, p source luminosity, E conversion efficiency of matter into radiation, \(\Omega\) jet opening angle, c speed of light, m_h  mass of hydrogen proton, and R a constant.