Nonthermal Emission and Magnetic Fields

  • Yoshiaki Sofue
Chapter
Part of the Lecture Notes in Physics book series (LNP, volume 935)

Abstract

Radio observations of the synchrotron radiation from the galactic disk and its polarization give us information about the magnetic field structure of the galaxy. Analyses of polarization vectors and of Faraday rotation measures along the line of sight give us information about the three-dimensional orientation of magnetic fields.Magnetic fields are in pressure equilibrium with the interstellar medium on the order of ∼ 10−12 ergs cm−3. These fields are coupled with interstellar gas, often termed “frozen in” to each other, and influence the hydrodynamic structure of the galactic disk.In the central regions, the magnetic fields accumulate to create strong vertical fields, which are wound by galactic rotation, and produce cosmic jets from the nuclear disks, often exhibiting highlighted cosmic jets from active galactic nuclei nesting supermassive black holes.The strongest, and most compact, magnetic field thus far observed reaches ∼ 1012 G on the surface of neutron stars observed as pulsars. Galactic magnetic fields are on the order of several 10−6 G or ∼ 1 μG. Intergalactic fields are sometimes observed to exhibit about the same order as galactic, ∼ 1 μG.The largest-scale, but weaker, magnetic field may penetrate the universe. Thus far known celestial objects are all magnetized, from the Earth, the Sun, stars, interstellar matter, galaxies, and clusters of galaxies. Only one exception is the universe for which the cosmological isotropy principle is adopted. It might be rather challenging to ask if the universe has the north and south directed by a cosmological magnetic field.

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Copyright information

© Springer Nature Singapore Pte Ltd. 2017

Authors and Affiliations

  • Yoshiaki Sofue
    • 1
  1. 1.Institute of AstronomyThe University of TokyoMitakaJapan

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