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Light Curves and What They Can Tell Us

A light curve is a graph which shows the brightness of an object over a period of time. In the study of objects which change their brightness over time, such as novae, supernovae, and variable stars, the light curve is a simple but valuable tool to a scientist. A sample light curve is shown in Figure 1. The light curve is the graph, or plot, generated from the following data:
Date Brightness
Date Brightness
April 21 9.2 June 20 8.7
April 27 9.3 June 26 8.3
May 3 9.7 July 2 8.6
May 9 9.9 July 8 9.1
May 15 9.6 July 14 9.1
May 21 9.8 July 20 9.2
May 27 9.9 July 26 9.5
June 2 9.7 Aug 1 9.9
June 8 9.1 Aug 7 9.7
June 14 8.8 Aug 13 9.7

Example light curve of a variable star

Figure 1

The plot shows the brightness of a certain astronomical object viewed through a telescope every 6 days over the course of a few months. This gives us a light curve of the object we have measured. But light curves can be generated for any measure of brightness which is repeated over and over in time. So, if I measured the number of X-rays being emitted by a star during every second for an hour, I could generate a light curve from my observations. Astronomers call these plots light curves because it is usually some part of the electromagnetic spectrum that we measure as a function of time and use to help us understand our universe.

How do we use light curves to tell us something useful?

The record of changes in brightness that a light curve provides can help astronomers understand processes at work within the star (or stellar system) and identify specific categories (or classes) of stellar events. For example, once a light curve has been made for a certain stellar object, it can be compared to standard light curves to help identify the type of object being studied.

If the light curve you measured looked like Figure 2, then you could identify your object as an eclipsing binary star. We can also tell from this light curve that it takes 10 days for one of the stars in the binary to orbit completely around the other. Astronomers would say "the orbital period of the binary system is 10 days."

Example light curve of an eclipsing binary star system

Figure 2

If the light curve looked like Figure 3, scientists would know that this signals the death of a star by a massive explosion called a supernova!

Example light curve of a supernova

Figure 3

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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