Glossary term: Star
Description: A star is a ball of plasma – atomic nuclei separated from their electrons – that is held together by its own gravity, and prevented from collapse by inner pressure that is the consequence of nuclear fusion processes in the star's core regions. Astronomers, in a slight abuse of physical terminology, commonly use "gas" and "plasma" interchangeably, and hence also refer to stars as balls of gas. In the atmosphere of a star the plasma may only be partially ionized and (depending on the temperature of the star) even contain some atoms.
The star closest to Earth is the Sun.
In a more general sense, the word "star" is taken to include protostars where nuclear fusion has not yet begun, and stellar remnants such as neutron stars or white dwarfs, which are two possibilities (depending on mass) for what stars turn into once they have exhausted the fuel for their nuclear fusion. Such stellar remnants are not simply plasma balls – a white dwarf can crystallize into an unusual kind of solid after cooling down for billions of years, and neutron stars bear a close similarity to gigantic atomic nuclei.
Whether viewed with the naked eye or with visible-light telescopes, stars are the most obvious objects in the night sky. In the cosmos, they are typically found within galaxies, each star generally accompanied by one or more planets. The study of how stars form and evolve is an important subfield of astrophysics.
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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
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A gravitational lens magnifies one of the first stars
Credit: NASA, ESA, B. Welch (JHU), D. Coe (STScI), A. Pagan (STScI) credit link
License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
Watchtower and Paddy Fields Under the Starry Sky
Credit: Likai Lin/IAU OAE
License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
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