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The Cloudy Universe

Published online by Cambridge University Press:  05 March 2013

Mark Walker  and
Mark Wardle
Mark Walker
Affiliation:
Special Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, NSW 2006, Australia; M.Walker@physics.usyd.edu.au
Mark Wardle
Affiliation:
Special Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, NSW 2006, Australia; M.Wardle@physics.usyd.edu.au
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Abstract

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Modelling of extreme scattering events suggests that the Galaxy's dark matter is an undetected population of cold, AU-sized, planetary-mass gas clouds. None of the direct observational constraints on this picture—thermal/non-thermal emission, extinction and lensing—are problematic. The theoretical situation is less comfortable, but still satisfactory. Galactic clouds can survive in their current condition for billions of years, but we do not have a firm description for either their origin or their evolution to the present epoch. We hypothesise that the proto-clouds formed during the quark–hadron phase transition, thereby introducing the inhomogeneity necessary for compatibility with light element nucleosynthesis in a purely baryonic universe. We outline the prospects for directly detecting the inferred cloud population. The most promising signatures are cosmic-ray-induced Hα emission from clouds in the solar neighbourhood, optical and X-ray flashes arising from cloud–cloud collisions, ultraviolet extinction, and three varieties of lensing phenomena.

Keywords

dark mattergalaxies: halosISM: clouds
Type
Research Article
Information
Publications of the Astronomical Society of Australia , Volume 16 , Issue 3 , 1999 , pp. 262 - 272
Copyright
Copyright © Astronomical Society of Australia 1999

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