Variable Stars

A variable star is a star where its brightness as seen from Earth fluctuates. The study of variable stars involves the recording of its magnitude, and how that fluctuates over time. The plotting of a variable star's magnitude vs. time is known as a light curve. The light curve plotting of variable stars combined with the study of supernovae events help physicists understand the formation of the universe.

Classification

Variable stars may be either intrinsic or extrinsic.

• Intrinsic variable stars: stars where the variability is being caused by changes in the physical properties of the stars themselves. This category can be divided into three subgroups.
  • Pulsating variables, stars whose radius alternately expands and contracts as part of their natural evolutionary ageing processes.
  • Eruptive variables, stars who experience eruptions on their surfaces like flares or mass ejections.
  • Cataclysmic or explosive variables, stars that undergo a cataclysmic change in their properties like novae and supernovae.

• Extrinsic variable stars: stars where the variability is caused by external properties like rotation or eclipses. There are two main subgroups.
  • Eclipsing binaries, double stars where, as seen from Earth's vantage point the stars occasionally eclipse one another as they orbit.
  • Rotating variables, stars whose variability is caused by phenomena related to their rotation. Examples are stars with extreme "sunspots" which affect the apparent brightness or stars that have fast rotation speeds causing them to become ellipsoidal in shape.

These subgroups themselves are further divided into specific types of variable stars that are usually named after their prototype. For example, dwarf novae are designated U Geminorum stars after the first recognized star in the class, U Geminorum.