A fourth state of matter composed of superheated gases in the form of charged particles. The matter inside a star and most of the matter scattered across the universe is in the form of plasma. Examples include the solar corona and solar wind, both of which consist predominantly of protons and electrons.
- ^ Baumann, Mary K.; Will Hopkins, Loralee Nolletti, Michael Soluri, Steven Hawking (foreword) and Ray Villard (astronomy consultant) (2007). Cosmos: Images From Here to the Edge of the Universe. London: Duncan Baird Publishers. ISBN 1844834761.
- ^ Rees, Martin (ed.) (2008). Universe: The Definitive Visual Guide. Dorling Kindersley Inc. ISBN 9780756636708.