For more than 200 years, astronomers thought that most of the stars in our galaxy had stellar companions. But a new study suggests the bulk of them are born alone and never have stellar company.
Since planets are believed to be easier to form around single stars, the discovery could mean planets are more common as well.
Conventional wisdom on double star systems, called binaries, goes as far back as the late 1700s. More sophisticated observations made in the 20th century seemed to confirm the numerical dominance of pairs.
Stellar surveys found that more than half of all Sun-like stars were part of multiple systems. For more massive stars, like O- and B-type stars, the number was estimated to be as high as 80 percent.
A few stars, like the North Star, Polaris, have two or more companions.
"If you go out and look at the all visible stars in the night sky and ask, ‘How many of those are binary?’ the answer is, ‘Most of them,’" said study author Charles Lada of the Harvard-Smithsonian Center for Astrophysics (CfA). "The assumption was that because most bright stars were binaries, all stars would tend to be binaries."
The catch, however, is that most stars in the Milky Way are not bright stars like our Sun, but dim, low-mass stars called red dwarfs.
Red dwarfs
Scientists estimate that red dwarfs make up to 85 percent of the stars in our Galaxy. These stars are about one-fifth as massive as the Sun and up to 50 times fainter.
Red dwarfs are so dim that it’s only been in the past decade or so that technology has improved to the point where astronomers can study them in detail. And they’ve found that only about 25 percent of red dwarfs have stellar companions.
Lada concludes that upwards of two-thirds of all star systems in the galaxy are single, red dwarf stars. His finding, announced today, was detailed in a recent online edition of Astrophysical Journal Letters.
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