Van Biesbroeck’s Star

Stars come in all types, from brilliant to feeble. The brilliant ones are easy to see. But the feeble ones are a challenge just to discover, let alone study. This month marks the 75th anniversary of the discovery of the most feeble star then known.

Georges Van Biesbroeck was an astronomer at Yerkes Observatory in Wisconsin. He specialized in double stars — two stars locked in a mutual orbit around each other. He measured the positions of known double stars, and discovered new ones.

In 1940, he took a photographic plate of a faint red star in the constellation Aquila. Three years later, he was using McDonald Observatory’s 82-inch telescope to take new plates of some nearby stars. He hoped the pictures would reveal companions of some of those stars.

In late October of 1943, one of those plates included the faint star in Aquila. The plate revealed a previously unseen companion close to the main star. The new star moved through space in the same direction as the main star, indicating they were a pair — moving as a single unit.

Known today as Van Biesbroeck’s Star, the companion is one of our closest neighbors — just 19 light-years away. As Van Biesbroeck noted in his discovery paper, though, the star is a bare ember: If you put it in place of the Sun, it would look about as bright as the full Moon.

Van Biesbroeck’s Star remained the low-luminosity champion for years — until an even fainter star was discovered in the 1980s.

Script by Ken Croswell