Description
Recent observations indicate that galactic-scale bubbles are more prevalent than previously thought. Our Milky Way hosts the giant Fermi Bubbles, which are highly symmetric large gamma-ray structures emanating from the Galactic Centre and located both above and below the Galactic plane. The galaxy NGC 3079 also has galactic-scale bubbles, but they are considerably smaller than the Fermi Bubbles of the Milky Way. The structure and the emission of these bubbles seem to differ across galaxies. We speculate that galactic outflows such as those in the starburst galaxy M82 may be post-breaking-out phase of bubbles. In this unified scenario, the power of outflows driven by mini AGN jets and nuclear starbursts would be a continuous parameter, and some would fall within a certain range for a given galactic environment to exhibit a prominent bubble-like structure. While current literature strongly supports a leptonic spectral origin for the Fermi bubbles, a simplistic leptonic model is unable to accommodate the complexity of the environments and the bubble and flow dynamics for a spectrum of galaxies due to the constraint set by rapid cooling of leptons when compared to other relevant timescales, including the dynamical timescale of the host galaxies. We investigate a more general lepto-hadronic scenario by varying combinations of cosmic ray hadron and lepton densities and determine the dynamical evolution of these bubbles and the condition leading to its outburst to initiate the large-scale outflows. We present our model and the dynamical equations governing the bubble's dynamics, thus showing their different evolutionary stages.
