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A lower limit of 50 microgauss for the magnetic field near the Galactic Centre

Crocker, Roland M. and Jones, David I. and Melia, Fulvio and Ott, Jürgen and Protheroe, Raymond J. (2010) A lower limit of 50 microgauss for the magnetic field near the Galactic Centre. Nature, 463 (1). pp. 65-67. ISSN 0028-0836.

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The amplitude of the magnetic field near the Galactic Centre has been uncertain by two orders of magnitude for several decades. On a scale of ~100 parsecs (pc), fields of ~1,000 microgauss (μG; refs 1–3) have been reported, implying a magnetic energy density more than 10,000 times stronger than typical for the Galaxy. Alternatively, the assumption of pressure equilibrium between the various phases of the Galactic Centre interstellar medium (including turbulent molecular gas, the contested^4 ‘very hot’ plasma, and the magnetic field) suggests fields of ~100 μG over ~400 pc size scales^5. Finally, assuming equipartition, fields of only ~6 μG have been inferred from radio observations^6 for 400 pc scales. Here we report a compilation of previous data that reveals a downward break in the region's non-thermal radio spectrum (attributable to a transition from bremsstrahlung to synchrotron cooling of the in situ cosmic-ray electron population). We show that the spectral break requires that the Galactic Centre field be at least ~50 μG on 400 pc scales, lest the synchrotron-emitting electrons produce too much γ-ray emission, given other existing constraints^7. Other considerations support a field of 100 μG, implying that over 10% of the Galaxy's magnetic energy is contained in only ≲0.05% of its volume.

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Ott, Jürgen0000-0001-8224-1956
Additional Information:© 2010 Macmillan Publishers Limited. Received 25 November 2008; Accepted 30 October 2009. R.M.C. thanks T. Porter for conversations about the Galactic Centre interstellar radiation field. D.I.J. thanks Monash University for hospitality. R.M.C. and D.I.J. thank J. Dickey for advice about radio data analysis. J.O. is a Jansky Fellow at NRAO; R.M.C. is a J. L. William Fellow at Monash University and a Marie Curie Fellow at Max-Planck-Institut für Kernphysik.
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Official Citation:Crocker, R. M., D. I. Jones, et al. (2010). "A lower limit of 50 microgauss for the magnetic field near the Galactic Centre." Nature 463(7277): 65-67. doi:10.1038/nature08635
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17844
Deposited By: Ruth Sustaita
Deposited On:14 May 2010 17:49
Last Modified:03 Oct 2019 01:34

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