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A strong, highly-tilted interstellar magnetic field near the Solar System

Abstract

Magnetic fields play an important (sometimes dominant) role in the evolution of gas clouds in the Galaxy, but the strength and orientation of the field in the interstellar medium near the heliosphere has been poorly constrained. Previous estimates of the field strength range from 1.8–2.5 μG and the field was thought to be parallel to the Galactic plane1 or inclined by 38–60° (ref. 2) or 60–90° (ref. 3) to this plane. These estimates relied either on indirect observational inferences or modelling in which the interstellar neutral hydrogen was not taken into account. Here we report measurements of the deflection of the solar wind plasma flows in the heliosheath4 to determine the magnetic field strength and orientation in the interstellar medium. We find that the field strength in the local interstellar medium is 3.7–5.5 μG. The field is tilted 20–30° from the interstellar medium flow direction (resulting from the peculiar motion of the Sun in the Galaxy) and is at an angle of about 30° from the Galactic plane. We conclude that the interstellar medium field is turbulent or has a distortion in the solar vicinity.

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Figure 1: Flows in the heliosheath as measured by Voyager 2.
Figure 2: Flows in the heliosheath for different B ISM directions.
Figure 3: Modelled flows as a function of the BISM.

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Acknowledgements

We thank the staff at NASA Ames Research Center for the use of the Columbia supercomputer. M.O. and F.A.B. acknowledge the support of NASA and the National Science Foundation. J.R. is supported by the Voyager project. V.V.I. acknowledges the support of the Russian Agency of Science and the Dynastia Foundation. We thank E. C. Stone and R. Shelton for suggestions and comments.

Author Contributions M.O. ran the models and wrote the paper. F.A.B. performed the R-H calculations, the model flow calculations, and participated in the writing of the paper. J.D.R. analysed the plasma data. G.T. helped implement the five-fluid magnetohydrodynamic model. V.V.I. assisted in the theoretical discussions, including solar cycle effects. T.I.G. provided assistance with the global magnetohydrodynamic model.

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Correspondence to M. Opher.

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This file contains Supplementary Data, Supplementary Table 1, a Supplementary Discussion, Supplementary References and Supplementary Figures S1-S4 with Legends. (PDF 696 kb)

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Opher, M., Bibi, F., Toth, G. et al. A strong, highly-tilted interstellar magnetic field near the Solar System. Nature 462, 1036–1038 (2009). https://doi.org/10.1038/nature08567

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