Evidence Of Water Near Dead Star

Astronomers have found extrasolar rocky bodies that could harbor water, but until now, chemical evidence of water’s presence has been lacking. Analysis of rocky debris surrounding a burned-out star has provided that evidence (Science 2013, DOI: 10.1126/science.1239447). The disk of debris around the white dwarf GD 61 contains remnants of a planetlike body ripped apart by the star’s gravity. From an estimate of oxygen’s abundance in the debris, researchers can infer water’s presence. Astronomer Jay Farihi of the University of Cambridge and coworkers measured oxygen’s and other elements’ spectral lines emanating from the vicinity of GD 61 with the Hubble Space Telescope and instruments at the W. M. Keck Observatory, in Hawaii. Plugging these data into white dwarf atmosphere models yielded elemental abundances. Carbon and metals, which react with oxygen to form CO₂ and metal oxides, were present, the researchers found, but not at high enough levels to account for oxygen’s abundance. The remaining oxygen likely exists in water, the researchers conclude. The findings suggest that rocky bodies can retain water after stars like the sun swell into red giants and then burn out, forming white dwarfs.