Sizing up small stars

Combining the light from two of the world’s largest visible-light telescopes, astronomers have measured, for the first time with high accuracy, the size of a small star. The diminutive body, Proxima Centauri, lies just 4.2 light-years from Earth and is the known star nearest to our solar system. Weighing in at only 15 percent of the sun’s mass, the star is one of many faint, small stars in our galaxy.

Damien Ségransan of the Observatory of Geneva in Sauverny, Switzerland, and his colleagues combined the starlight collected from two of the four 8-meter telescopes collectively known as the Very Large Telescope in Paranal, Chile. Rather than producing an image, this light-gathering process creates an interference pattern of light and dark bands. By analyzing that pattern, astronomers imaged Proxima Centauri as a disk instead of a point. They similarly measured the diameter of three other very small stars. The feat is similar to measuring from Earth the height of a child on the surface of the moon.

In agreement with predictions, Proxima Centauri has a diameter of 202,000 kilometers, or about one-seventh the girth of the sun, the astronomers report in an upcoming Astronomy & Astrophysics.


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