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

Abstract

The Galactic Centre contains a supermassive black hole with a mass of four million Suns1 within an environment that differs markedly from that of the Galactic disk. Although 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 surroundings2. Also, although the levels of star formation in the Galactic Centre have been approximately constant over the past few hundred million years, there is evidence of increased short-duration bursts3, strongly influenced by the interaction of the black hole with the enhanced gas density present within the ring-like central molecular zone4 at Galactic longitude |l| < 0.7 degrees and latitude |b| < 0.2 degrees. The inner 200-parsec region is characterized by large amounts of warm molecular gas5, a high cosmic-ray ionization rate6, unusual gas chemistry, enhanced synchrotron emission7,8, and a multitude of radio-emitting magnetized filaments9, the origin of which has not been established. Here we report radio imaging that reveals a bipolar bubble structure, with an overall span of 1 degree by 3 degrees (140 parsecs × 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 × 1052 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.

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Fig. 1: Radio emission from the Galactic Centre bubbles.
Fig. 2: Major features of the Galactic Centre radio bubbles.

Data availability

The data that support the findings of this study are available from a corresponding author upon reasonable request.

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Acknowledgements

The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. We acknowledge use of the Inter-University Institute for Data Intensive Astronomy (IDIA) data intensive research cloud for data processing. IDIA is a South African university partnership involving the University of Cape Town, the University of Pretoria and the University of the Western Cape. This research made use of Montage, which is funded by the US National Science Foundation under grant number ACI-1440620, and was previously funded by the National Aeronautics and Space Administration’s Earth Science Technology Office, Computation Technologies Project, under cooperative agreement number NCC5-626 between NASA and the California Institute of Technology. I.H. acknowledges support from the Oxford Hintze Centre for Astrophysical Surveys, which is funded through generous support from the Hintze Family Charitable Foundation. F.Y.-Z. is partially supported by grant AST-0807400 from the US National Science Foundation.

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Authors and Affiliations

Authors

Contributions

I.H. and F.C. planned the MeerKAT observations presented here. I.H. performed the calibration and imaging of the observations. I.H. wrote the manuscript together with F.Y.-Z., F.C. and W.D.C. All other authors have contributed to one or more of the planning, design, construction, commissioning or operation of the MeerKAT radio telescope.

Corresponding authors

Correspondence to I. Heywood or F. Camilo.

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Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Peer review information Nature thanks Maria Chernyakova and Roland Crocker for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Fig. 1 Spectral-index map of the region surrounding the southern tip of the radio bubbles.

A single sub-band image at 1,123 MHz from pointing GCXS30 (see Extended Data Table 1), convolved to 30-arcsec resolution and corrected for primary-beam attenuation effects, is shown in greyscale. Overlaid upon this is a map of the spectral index, derived by fitting for this quantity through an image cube formed from five such sub-band images (see Extended Data Table 2). The spectral-index values for features that have a high signal-to-noise ratio detection in each sub-band can be reliably measured using this method, with values as indicated by the colour bar. The mean and 1σ spectral-index values for two such extended regions are marked on the map (in the format \(\bar{\alpha }\) = mean ±1σ) and are consistent with non-thermal synchrotron emission. The spectral indices of the additional compact sources marked A–E are also measured for verification purposes, with the results listed in Extended Data Table 3.

Extended Data Table 1 IDs and pointing centres for the MeerKAT observations
Extended Data Table 2 Central frequencies of the eight sub-band images
Extended Data Table 3 Additional spectral-index measurements for verification purposes

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Heywood, I., Camilo, F., Cotton, W.D. et al. Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event. Nature 573, 235–237 (2019). https://doi.org/10.1038/s41586-019-1532-5

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