Glossary term: Variable Star

Redirected from Cataclysmic Variable

Description: A variable star is a star that shows marked changes in brightness over time to observers. The brightness of all stars changes over millions or billions of years due to stellar evolution. The term variable star is typically reserved for stars whose brightness varies on timescales much shorter than their evolutionary timescales.

There are several possible physical mechanisms that can lead to variability. Some stars, such as Cepheid variables or RR Lyrae stars, are unstable and pulsate, changing their size and brightness.

Other stars can eject bright material that increases the overall observed brightness ("eruptive variables"). Stars called cataclysmic variables or novae show a sudden increase in brightness followed by a return to their previous level. In such systems, the scenario involves a pair of stars, with matter from one flowing onto the other, and igniting in a nuclear fusion reaction as soon as a certain threshold is reached. One companion or the other undergoes the cataclysmic explosion and brightening.

Other stars appear variable because they are rotating, showing us alternately a brighter and a less bright side, or because there are really two stars orbiting each other, with one star periodically being eclipsed behind its companion. This latter class of binary is known as an eclipsing binary.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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