Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by
  an energetic event
  The Galactic Centre contains a supermassive black hole with a mass of 4
million suns within an environment that differs markedly from that of the
Galactic disk. While the black hole is essentially quiescent in the broader
context of active galactic nuclei, X-ray observations have provided evidence
for energetic outbursts from its surroundings. Also, while the levels of star
formation in the Galactic Centre have been approximately constant over the last
few hundred Myr, there is evidence of elevated short-duration bursts, strongly
influenced by interaction of the black hole with the enhanced gas density
present within the ring-like Central Molecular Zone at Galactic longitude |l| <
0.7 degrees and latitude |b| < 0.2 degrees. The inner 200 pc region is
characterized by large amounts of warm molecular gas, a high cosmic ray
ionization rate, unusual gas chemistry, enhanced synchrotron emission, and a
multitude of radio-emitting magnetised filaments, the origin of which has not
been established. Here we report radio imaging that reveals bipolar bubbles
spanning 1 degree x 3 degrees (140 parsecs x 430 parsecs), extending above and
below the Galactic plane and apparently associated with the Galactic Centre.
The structure is edge-brightened and bounded, with symmetry implying creation
by an energetic event in the Galactic Centre. We estimate the age of the
bubbles to be a few million years, with a total energy of 7 x 10^52 ergs. We
postulate that the progenitor event was a major contributor to the increased
cosmic-ray density in the Galactic Centre, and is in turn the principal source
of the relativistic particles required to power the synchrotron emission of the
radio filaments within and in the vicinity of the bubble cavities.
