Astronomers have discovered water vapour in the atmosphere of a giant red carbon star, thereby overturning scientists' belief that the formation of water vapour in the atmosphere of such stars is impossible. The discovery was made with the Herschel telescope by a team of astronomers from the University of Amsterdam (UvA) and Katholieke Universiteit Leuven, led by Leen Decin. The finding was published in the 2 September issue of Nature.
Water and carbon molecules are the building blocks for life on Earth. These are generated in huge quantities inside stars like our sun near the end of their life spans. When these stars grow older they expand to form red giants and expel their atmospheres. These atmospheres could contain either water molecules or carbon molecules. It was thought that these two types of molecules could not coexist. However, with the discovery of excess water vapour in the atmosphere of a carbon-rich red giant - achieved using the PACS and SPIRE instruments on ESA's Herschel Space Observatory - this idea has been jettisoned.
Red giant star CW LeonisCW Leonis is a red giant star located in the constellation Leo. Though only a few times as heavy as the sun, the star has expanded to a size that would fit our sun a few hundred times over. CW Leonis will soon reach the end of its lifespan and become a white dwarf enveloped by a planetary mist comprised of gas and dust drawn from the material in its atmosphere.
With so much carbon in that atmosphere, any oxygen should, in theory, be locked inside carbon monoxide molecules. By extension, there should also be no water vapour. However, observations made on one wavelength in 2001 did reveal water vapour. At the time, it was thought that stellar wind was evaporating water molecules from icy comets orbiting the star. However, the recent observations with Herschel have detected water vapour on additional wavelengths, and have made it possible to calculate temperatures. Temperatures of up to 1000 degrees indicate the presence of water vapour throughout the stellar wind, even close to the surface of the star itself. Decin and her team now believe this water vapour to be the result of unexpected chemical processes set in motion by ultraviolet light. Ultraviolet light acts to break down carbon monoxide, releasing oxygen atoms that subsequently bond with hydrogen to form water molecules.