What’s a light curve?

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A light curve is a graph of visible light from stars over time, used to determine the behavior of a star. The light-tracing technique is important for variable stars, which change brightness in both regular and unpredictable ways. Light curves can also be used to describe the action of binary stars, which are two stars traveling around each other.

Variable stars can change brightness in regular patterns, due to rotation of the star or interaction with other stars. A variable binary occurs because the two stars move relative to each other, and one can block the other’s light as they move. Visible light graphs or plots can be derived from visual observations by astronomers or from computer models using digital light equipment.

Some stars can show varying light patterns over several years, so repeated observations are needed to develop a good curve. Although astronomers can assign different light values ​​for the same star over time, the light curve can be accurate because the many observations are plotted together and averaged. Many astronomers believe that light curves from visual observations are as accurate as computer models.

The binary behavior of stars can be measured using this method, due to an effect called an eclipse. In the same way that the moon can eclipse the sun and block its light when viewed from Earth, a star in a binary pair can eclipse the other. When this occurs, the visible light seen through a telescope will change and a light curve can be used to plot measurements. If the behavior of the eclipse occurs on a regular basis over time, the data can be used to determine the rotation period, or the time it takes for the binary stars to rotate around each other.

Another use of the light curve is to observe a supernova, which is an exploding star. Some stars reach a point in their lives where the star rapidly collapses under gravitational forces, then explodes. The result is a large increase in visible light as the star’s gases expand outward at high speed, and the observations can be used to estimate the outward velocity of the star’s gases and the supernova’s distance from Earth.

Supernova explosions are divided into several classes based on how the explosion occurs. Some stars dim rapidly after their outburst, while others reach a certain level of light and remain there for a certain time, called plateau behavior. These differences would not be apparent using individual observations, which can make a light curve useful for classification. The classes of supernovae also create different elements from the chemical reactions that occur during explosions, and the curves can help determine the chemical compositions of the star’s expanding gases and remaining core material.

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