Unveiling the Origin of the Fermi Bubbles
  The Fermi bubbles, two giant structures above and below the Galactic center
(GC), are among the most important discoveries of the Fermi Gamma-ray Space
Telescope. Studying their physical origin has been providing valuable insights
into cosmic-ray transport, the Galactic magnetic field, and past activity at
the GC in the Milky Way galaxy. Despite their importance, the formation
mechanism of the bubbles is still elusive. Over the past few years there have
been numerous efforts, both observational and theoretical, to uncover the
nature of the bubbles. In this article, we present an overview of the current
status of our understanding of the bubbles' origin, and discuss possible future
directions that will help to distinguish different scenarios of bubble
formation.
