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Giant magnetized outflows from the centre of the Milky Way

Abstract

The nucleus of the Milky Way is known to harbour regions of intense star formation activity as well as a supermassive black hole1. Recent observations have revealed regions of γ-ray emission reaching far above and below the Galactic Centre (relative to the Galactic plane), the so-called ‘Fermi bubbles’2. It is uncertain whether these were generated by nuclear star formation or by quasar-like outbursts of the central black hole3,4,5,6 and no information on the structures’ magnetic field has been reported. Here we report observations of two giant, linearly polarized radio lobes, containing three ridge-like substructures, emanating from the Galactic Centre. The lobes each extend about 60 degrees in the Galactic bulge, closely corresponding to the Fermi bubbles, and are permeated by strong magnetic fields of up to 15 microgauss. We conclude that the radio lobes originate in a biconical, star-formation-driven (rather than black-hole-driven) outflow from the Galaxy’s central 200 parsecs that transports a huge amount of magnetic energy, about 1055 ergs, into the Galactic halo. The ridges wind around this outflow and, we suggest, constitute a ‘phonographic’ record of nuclear star formation activity over at least ten million years.

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Figure 1: Linearly polarized intensity P at 2.3 GHz from S-PASS.
Figure 2: Lobes' polarized intensity and γ-ray spurs.
Figure 3: Polarized intensity and magnetic angles at 23 GHz from WMAP8.
Figure 4: The vertical range of cosmic ray electrons as a function of their kinetic energy, Ee.

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Acknowledgements

This work has been carried out in the framework of the S-band Polarization All Sky Survey collaboration (S-PASS). We thank the Parkes Telescope staff for support, both while setting up the non-standard observing mode and during the observing runs. R.M.C. thanks F. Aharonian, R. Beck, G. Bicknell, D. Jones, C. Law, M. Morris, C. Pfrommer, W. Reich, A. Stolte, T. Porter and H. Völk for discussions, and the Max-Planck-Institut für Kernphysik for supporting his research. R.M.C. also acknowledges the support of a Future Fellowship from the Australian Research Council through grant FT110100108. B.M.G. and C.P. acknowledge the support of an Australian Laureate Fellowship from the Australian Research Council through grant FL100100114. M.H. acknowledges the support of research programme 639.042.915, which is partly financed by the Netherlands Organisation for Scientific Research (NWO). The Parkes Radio Telescope is part of the Australia Telescope National Facility, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. We acknowledge the use of WMAP data and the HEALPix software package.

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Authors

Contributions

E.C. performed the S-PASS observations, was the leader of the project, developed and performed the data reduction package, and did the main analysis and interpretation. R.M.C. provided theoretical analysis and interpretation. L.S.-S., M.H. and S.P. performed the S-PASS observations. M.J.K. performed the telescope special set-up that allowed the survey execution. L.S.-S., M.H., B.M.G., G.B., M.J.K. and S.P. were co-proposers and contributed to the definition of the project. C.P. performed the estimate of the Hα depolarizing region distance. E.C. and R.M.C. wrote the paper together. All the authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Ettore Carretti.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data 1-9, Supplementary Tables 1-3, additional references and Supplementary Figures 1-6. (PDF 1098 kb)

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Carretti, E., Crocker, R., Staveley-Smith, L. et al. Giant magnetized outflows from the centre of the Milky Way. Nature 493, 66–69 (2013). https://doi.org/10.1038/nature11734

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