New Model of Intergalactic Magnetic Fields

On Earth, strong magnetic fields, powered by currents moving through wires, steer energetic particles around an accelerator. At the Sun, magnetic fields, powered by immense subsurface currents, spring upwards to facilitate the warming of the Sun's corona and, further downstream, to buffet the Earth and sometimes disrupt our terrestrial telecommunications.

But where do the fields in the intergalactic medium (IGM) come from, and what role do they play in the life of the cosmos? Such fields have been observed to reside even in parts of space relatively devoid of galaxies.

Earlier theories of IGM fields, such as the ideas that the fields may be partly primordial in nature (present at the creation) or that they grew as a result of shock waves occurring at the boundary between massive colliding gas clouds, must now be amended to include the substantial contribution of galactic black holes.

Philipp Kronberg and Quentin Dufton at the University of Toronto (kronberg@physics.utoronto.ca, 416-978-4971) and Hui Li and Stirling Colgate at Los Alamos believe that fully half of the energy content of those massive radio-emitting lobes (up to 10⁶⁰ ergs) exists in the form of magnetic energy thrown out of hundred-million-solar-mass black holes. This represents about 10% of their total gravitational energy (about 10⁶¹ ergs).

This latter energy, summed over many galaxies, appears to be the largest available energy reservoir in the mature universe for magnetizing intergalactic space. They also suggest that the fields don't stop there but continue on to fill up large volumes of space, even those rural areas between galaxy clusters. These expelled magnetic fields should exert a substantial influence on galaxy formation. The dynamo process whereby black holes would crank out so much energy and such strong fields remains one of the greatest problems in astrophysics. (Astrophysical Journal, 10 October 2001; Los Alamos preprint.)