Studies of star-forming regions indicate that binary stars start off with a uniform distribution of orbital periods: the number of binaries younger than a few million years that orbit each other every 1–10 years, 10–100 years, 100–1,000 years, and so on, is about the same. but with older binaries, the most common orbital period is about 200 years, and both shorter and longer periods are rarer.
The scarcity of binaries with longer orbital periods is easy to explain: to have a long orbital period, the stars must be quite far apart. But where did the short-period binaries go? Now three astronomers think they have the answer: the interactions between the two can modify the stars' orbits, causing them to spiral towards each other until they merge and become a single star.