The unexpected recent discovery of the so-called Fermi bubbles–large, diffuse γ-ray structures that form a bipolar shape above and below the Galactic plane–has revived interest in characterizing the GW in the Milky Way [131, 132]. Previous data provided strong evidence of its existence (see references in [21]), but the picture-perfect morphology of the Fermi bubbles make it an almost inarguable fact.
This review is concerned with observations of starburst-driven GWs, and the Milky Way’s GW may be driven by star formation (e.g., [133]). It also may be powered by the Galactic nuclear black hole during a previous accretion episode (see, e.g., the recent review of relevant data and models in [134]). However, for completeness we note some recent observations, since the Milky Way is an excellent laboratory for studying a GW at high sensitivity and spatial resolution in what is a “typical” galaxy in the Local Universe. Since its discovery, the Fermi bubbles have notably been found to also contain a magnetized radio plasma [135] and have been connected to the previously known microwave “haze” that was re-observed with Planck [136]. The bubbles also appear to host neutral gas clouds moving up to several hundred km s−1 [137, 138, 139], as well as higher-ionization species observed in absorption [140, 141, 142, 143]. These neutral and ionized clouds may lie along filaments swept up by the bubble along its edges, though their contribution to the structure and mass/energy budget of the outflow are not yet clear.
A recent claim has also been made for a GW in a satellite of the Milky Way. This potential outflow in the Large Magellanic Cloud was extrapolated from absorption-line measurements of a single line of sight through its disk [144]. The LMC contains 30 Doradus, which is undergoing a significant star formation episode.