Science: Siamese Stars

Not all stars travel alone, like the sun. Many are paired, the two members revolving around each other like the ends of a spinning dumbbell. Such bright stars as Capella, Spica, Castor, Mizar (a Big Dipper star) and Algol (the “Demon Star”) are binaries (doubles). Some stars occur in groups of more than two. Astronomers estimate that one-fourth or more of all the stars in the sky are doubles or multiples. Last week astronomers heard of a pair of stellar Siamese twins.

Sometimes the stars of a binary are so close together that even the most powerful telescopes show them as one.* But if their orbits are nearly edgewise to earth, then one star will periodically eclipse the other, and the light will correspondingly vary. By timing the eclipses, astronomers can tell approximately how far apart the two stars are.

A remarkable eclipsing binary is the star Beta Lyrae, in the constellation of Lyra (The Harp). Astronomers have long known that its two components must be exceedingly close together, for one has hardly stopped eclipsing the other before the other starts eclipsing the first. Dr. Gerard Peter Kuiper of the University of Chicago’s Yerkes Observatory last week surmised that the two stars comprising Beta Lyrae are in actual contact, like snowballs crushed together.

At an astronomical meeting at Wellesley, Mass., Dr. Kuiper pictured star material rushing from the larger of the Beta Lyrae pair into the smaller at speeds around 200 miles per second—so fast that some of it is hurled clear beyond the small star to form a tail like a comet’s. As the stars revolve the tail is dragged around behind them, like a lagging feather.

*No star is near enough to earth for its image to appear in the telescope as a disc (as do the images of solar planets). If it were not for atmospheric diffusion and imperfections of the instrument, which convert star images into undulant blobs, they would appear in the telescope as sharp pinpoints of light.