Astronomers have debated for decades as to why blue stragglers don’t show their age. It’s been hypothesized that they must have come across extra hydrogen fuel that helped them burn hotter, but it was uncertain whether they did so by merging with other stars, colliding with victims or stealing hydrogen from companions. People have been trying to explain the origin of blue stragglers since their discovery in 1953. Now researchers have evidence that blue stragglers are indeed cannibals that rip fuel off their neighbors. They used the WIYN Observatory in Tucson, Ariz., to analyze 21 blue stragglers in NGC 188, a 7 billion year old cluster of about 3,000 stars in the constellation Cepheus, located in the sky near Polaris, the North Star.
The majority of blue stragglers in the study are in binaries, they have a companion star. The light from the blue stragglers’ companion stars is not actually visible, but their effect on the blue stragglers is evident, with each companion pulling gravitationally on its blue straggler and creating a “wobble” as it orbits. According to Aaron Geller, an astronomer at Northwestern University it’s really the companion star that helped determine where the blue straggler comes from. The companion stars orbit at periods of about 1,000 days, and they have evidence that the companions are white dwarfs. Both point directly to an origin from mass transfer.