Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event

TL;DR

This paper reports the discovery of bipolar radio bubbles in the Galactic Centre, formed by an energetic event a few million years ago, which likely contributed to cosmic-ray density and synchrotron emission in the region.

Contribution

It presents new radio imaging evidence of large bipolar bubbles in the Galactic Centre, linking them to a past energetic event and cosmic-ray enhancement.

Findings

Bipolar bubbles span 140x430 parsecs, extending above and below the Galactic plane.

Estimated age of the bubbles is a few million years.

Total energy of the bubbles is approximately 7 x 10^52 ergs.

Abstract

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.