A Violent Past
Our galaxy has a colossal secret. Towering above and below the galactic plane are two enormous structures known as the Fermi Bubbles, invisible to the naked eye but glowing fiercely in gamma rays. Discovered in 2010 by the Fermi Gamma-ray Space Telescope, these bubbles form a massive hourglass shape centered on the Milky Way's core. Each lobe extends 25,000 light-years into space, making the total structure 50,000 light-years tall—roughly half the diameter of the entire Milky Way. They are filled with a mix of very hot gas, cosmic rays and magnetic fields.
These bubbles suggest a cataclysmic event that occurred a few million years ago. The two leading theories both involve the galactic center. One model suggests the bubbles are the remnants of a powerful jet of matter blasted out from Sagittarius A*, the supermassive black hole at our galaxy's heart. This could have happened when the black hole devoured a massive cloud of gas and dust, releasing energy. An alternative theory proposes that a burst of rapid star formation and subsequent supernova explosions near the galactic center provided the energy required to inflate these structures. The total energy needed is estimated to be equivalent to about 100,000 supernovae.