Mystery of star's cloud of water solved

PARIS, Sept. 2 (UPI) -- A distant dying star surrounded by water is using an unexpected ingredient -- ultraviolet starlight -- to create it, European scientists say.

The European Space Agency's Herschel infrared space observatory discovered an unexpected cloud of water vapor around the ancient star IRC+10216, and researchers immediately began searching for the source, an ESA release said Thursday.

Stars like IRC+10216 are known as carbon stars and are thought not to make much water. At first researchers suspected the star's heat might be evaporating comets or even dwarf planets to produce the water. But sensitive instruments on the Herschel spacecraft revealed the water is too hot to have come from the destruction of icy celestial bodies.

The star is surrounded by a huge cloud of dust and gas, and astronomers say ultraviolet light from surrounding stars is reaching deep into the dust cloud and breaking up molecules such as carbon monoxide and silicon monoxide.

This releases oxygen atoms that then attach themselves to hydrogen molecules, forming water.

"This is the only mechanism that explains the full range of the water's temperature," Leen Decin of Katholieke Universiteit Leuven, Belgium, said.

The closer to the star the water is formed, the hotter it will be, he said.

"This is a good example of how better instruments can change our picture completely," Decin said.