The "bubble" structure is estimated to be "only" a few million years old.

NASA

he image: Through the lens of a NASA telescope, astronomer Doug Finkbeiner and colleagues recently made a stunning disovery: Two enormous bubbles "emerging like party balloons" above and below the Milky Way. The galaxy-sized bubbles, each of which extends 25,000 light-years beyond the Milky Way's boundaries, are expanding at the rapid clip of 2.2 million miles per hour and emitting massive amounts of gamma rays as they go. Where, exactly, did the "space bubbles" come from?
The reaction: The bubbles may be the result of "a wave of starbirth at the galaxy’s center millions of years ago," says Ron Cowen at Science News. The stars' "explosive deaths" could have emitted enough energy to create such huge growths. A more plausible theory involves the "supermassive black hole" that scientists know "resides at the center of our galaxy." That region of space "must go through stages when it gobbles up massive amounts of material," says John Roach at National Geographic, and such activity could be the cause of the gamma ray-spewing structures. Check out images of the the Milky Way's majestic bubbles: