Sgr A\* accretion event rather than from nuclear star formation.'
author:
- 'Matthew J. Miller & Joel N. Bregman'
title: 'The Interaction of the Fermi Bubbles with the Milky Way’s Hot Gas Halo'
---

Introduction {#section.introduction_chap_fb}
============

The Fermi bubbles are important Galactic structures that were recently discovered by the *Fermi Gamma-ray Space Telescope* [@su_etal10]. The bubbles are two diffuse lobes of material extending $\sim$50$\arcdeg$ above and below the Galactic plane ($\approx$10 kpc at the Galactic center). Their surface brightness shows little variation on the sky, their gamma-ray spectrum follows a power law with $dN/dE \propto E^{-2}$ between $\approx$1 and 200 GeV, and they have a counterpart in microwaves, known as the $Wilkinson\ Microwave\ Anisotropy\ Probe$ ($WMAP$) haze [@dobler_finkbeiner08; @dobler_etal10; @su_etal10; @ackermann_etal14]. It is still unclear what produces the gamma rays, but all plausible mechanisms imply that energetic cosmic-ray particles exist within the bubbles. This inference combined with the bubbles’ size and location on the sky suggests that they are affiliated with a massive energy injection event near the Galactic center.

The bubbles’ morphology is similar to wind-blown bubbles observed in other galaxies, indicating that they formed from either a period of enhanced nuclear star formation or a Sgr A\* 