11.7 Variable Stars and Novae

Sometimes a star will change luminosity not due to an eclipse, but due to some sort of physical characteristic. These are called variable stars or variables. These changes in brightness can range from 1/1000 of a magnitude to 20 magnitudes over a period of a fraction of a second to many years. Over 150,000 variables are known, and many others are suspected to be variables.

There are two major classes of variable stars: Pulsating Variables and Cataclysmic Variables. Pulsating variable stars swell and shrink, which affects the star’s brightness. One important class of pulsating variable stars is the Cepheid Variables.

Cataclysmic variables are binary stars, which consist of a white dwarf primary and an orbiting secondary star. The secondary star is transferring matter to the primary star. This causes the primary star to irregularly outburst a significant increase in brightness. Cataclysmic variables were originally called novae (singular: nova) from the Latin term new , since the star seemingly appeared out of nowhere.

Cataclysmic Variable

An illustration showing an artist’s concept of a double star, called a cataclysmic variable star system—showing a large or primary star and a smaller or secondary star.
Figure 11.17. the cataclysmic variable will eventually dim back down significantly until more stellar fuel is transferred from the secondary star to the primary star. This process will go on until there is no more stellar fuel to transfer. The primary star (upper right) is pulling stellar material off the secondary star (lower left). Once a significant amount of mass builds up on the primary star, it will outburst and brighten significantly. Then the star will dim back down, repeating the process as long as fuel is available from its secondary star.
Cataclysmic Variable Star by STSci, Public Domain.

Attribution

“Variable Stars” and “Cataclysmic Variables” from Introduction to Astronomy by Florida State College at Jacksonville and Dr. Mike Reynolds is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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Fanshawe College Astronomy Copyright © 2023 by Dr. Iftekhar Haque is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.