Origin of galactic and extragalactic magnetic fields

By L. Widrow. 2002

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A variety of observations suggest that magnetic fields are present in all galaxies and galaxy clusters. These fields are characterized by a modest strength ${(10}^{\ensuremath{-}7}\char21{}{10}^{\ensuremath{-}5}\mathrm{G})$ and huge spatial scale $(\ensuremath{\lesssim}1\mathrm{Mpc}).$ It is generally assumed that magnetic fields in spiral galaxies arise from the combined action of differential rotation and helical turbulence, a process known as the \ensuremath{\alpha}\ensuremath{\omega} dynamo. However, fundamental questions concerning the nature of the dynamo as well as the origin of the seed fields necessary to prime it remain unclear. Moreover, the standard \ensuremath{\alpha}\ensuremath{\omega} dynamo does not explain the existence of magnetic fields in elliptical galaxies and clusters. The author summarizes what is known observationally about magnetic fields in galaxies, clusters, superclusters, and beyond. He then reviews the standard dynamo paradigm, the challenges that have been leveled against it, and several alternative scenarios. He concludes with a discussion of astrophysical and early-Universe candidates for seed fields.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/4ed3b473c01020cae8938490a61222ebadb7d5ba

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Citations in the corpus

LOWER LIMIT ON THE STRENGTH AND FILLING FACTOR OF EXTRAGALACTIC MAGNETIC FIELDS (2011, background): “While magnetic fields are known to play a prominent role for the dynamics and in the energy budget of astrophysical systems on galactic and smaller scales, their role on larger scales is still elusive (Widrow 2002; Kulsrud & Zweibel 2008).”
Evolving turbulence and magnetic fields in galaxy clusters (2005, background): “The seed field itself can be produced by a wide range of mechanisms (Appendix A; see also Ruzmaikin et al. 1989; Widrow 2002; Brandenburg & Subramanian 2005).”
Simulations of the Small-Scale Turbulent Dynamo (2003, background): “…Heiles 1997; Vallée 1997, 1998; Balbus & Hawley 1998; Kulsrud 1999; Weiss & Tobias 2000; Title 2000; Beck 2000, 2001; Ferrière 2001; Kronberg et al. 2001; Carilli & Taylor 2002; Han & Wielebinski 2002; Widrow 2002; Tobias 2002; Ossendrijver 2003; Han et al. 2004; Brandenburg & Subramanian 2004).”
Planck 2015 results: XIX. Constraints on primordial magnetic fields (2015, neutral): “In addition to the ubiquitous presence of magnetic fields in the Universe, astrophysical observations show that some galaxies might have a helical magnetic field structure (Widrow 2002; Vallée 2004).”
The Astrophysics of Ultrahigh-Energy Cosmic Rays (2011, background): “Some models set their origins in the primordial Universe (see Widrow 2002 and references therein) other models through magnetic pollution from astrophysical sources such as galactic winds or jets from radio-galaxies (Kronberg et al. 1999; Birk et al. 2000; Aguirre et al. 2001; Cen et al. 2005;…”
EGMF Constraints from Simultaneous GeV-TeV Observations of Blazars (2011, background): “However, the origin of these fields remains largely uncertain (see Kronberg (1994); Grasso & Rubinstein (2001); Widrow (2002); Beck (2009) for reviews).”
Generation of large scale magnetic fields in single-field inflation (2007, background): “Magnetic fields are present on various scales in the Universe from planets, stars, galaxies, to clusters of galaxies, see e.g., Refs. [1, 2, 3 ] for reviews.”
Faraday rotation measure synthesis (2005, methodology): “Polarization observations at radio frequencies are an important diagnostic tool in the study of galactic and extragalactic magnetic fields (e.g. Kronberg 1994; Vallee 1997; Widrow 2002).”
Fluctuation dynamo and turbulent induction at low magnetic Prandtl numbers (2007, background): “…physical mechanism most likely to be responsible for the ubiquitous presence of dynamically strong magnetic fields in the Universe — from planets and stars to galaxies and galaxy clusters (e.g., Moffatt 1978, Childress & Gilbert 1995, Roberts & Glatzmaier 2000, Ossendrijver 2003, Widrow 2002).”
EVIDENCE FOR GAMMA-RAY HALOS AROUND ACTIVE GALACTIC NUCLEI AND THE FIRST MEASUREMENT OF INTERGALACTIC MAGNETIC FIELDS (2010, background): “…the dynamo action of the large-scale convective motions of gas, the fields in voids remain low, close to their primordial values modified only by the relatively small contribution of the fields leaking out of galaxies (Kronberg 1994; Grasso & Rubinstein 2001; Widrow 2002; Kulsrud & Zweibel 2008).”
X-Ray Thermal Coronae of Galaxies in Hot Clusters: Ubiquity of Embedded Mini-Cooling Cores (2006, background): “Our knowledge of the magnetic field in elliptical galaxies is also poor(reviewed by Widrow 2002).”