Why Most Bright Stars are Binary But Most Dim Stars Are Single: A Simple Qualitative Explanation

It is known that most visible stars are binary: they have a nearby companion star, and these two stars orbit around each other. Based on this fact, until recently, astronomers believed that, in general, most stars are binary. A few years ago, a surprising paper showed that while most bright stars are indeed binary, most dim stars are single. In this paper, we provide a simple qualitative explanation for this empirical fact. 1 Why Most Bright Stars are Binary But Most Dim Stars Are Single: An Empirical Fact That Needs to Be Explained Most visible stars are binary stars: an empirical fact. Since the 18th century, it has been known that many visible stars are binary. As the resolution of the astronomical instruments increased, more and more visible stars turned out to have star companions. At present, it is estimated that 75-80% of visible stars are binary stars; see, e.g., [1]. From this viewpoint, our Sun is an exception. Resulting conjecture: most stars are binary. Since most visible stars are binary, astronomers naturally concluded that in general, most stars are binary. This conclusion led to pessimistic estimates for the number of planets: it is very difficult for a binary star to have a stable planetary orbit, so the natural conclusion was that most stars do not have planets. Recent observation: most stars are single. Surprisingly, it turns out that most stars are single. This does not contradict to the fact that most visible stars are binary. Indeed, for a star to be visible to a naked eye at a large distance, this