Straggling stars maintain youth by feeding off neighbors

Ars Technica : Blue stragglers are stars that burn brighter, hotter, and bluer—and therefore look much younger—than neighboring stars that formed at the same time. It’s been theorized that they incorporated extra hydrogen, which helped them burn more intensely, but it wasn’t known whether they merged with other stars, collided with them, or stole hydrogen from companion stars. Aaron Geller of Northwestern University and colleagues used the WIYN Observatory in Tucson, Arizona, to analyze 21 blue stragglers in the cluster NGC 188, in the constellation Cepheus, and found that 16 of them have a companion star with about half the mass of our Sun. Theoretical models indicate that the mass transfer necessary for a giant main sequence star to feed its hydrogen and helium to a blue straggler would leave behind a carbon-oxygen-rich white dwarf of about that mass. Geller and his team are going to use the Hubble Space Telescope to confirm whether mass transfer is still taking place between the dwarf remnants and the stragglers they orbit.