Hot water discovered around a giant carbon star requires a new theory for the chemistry around stars to be explained. The new theory could significantly alter our understanding of what materials exist in interstellar space, and where water and life could exist in the universe.

"It makes us realize that the chemistry in all stars can be much more complex than we thought it was," said astronomer Leen Decin of the Instituut voor Sterrenkunde in Belgium, lead author of the study published Sept. 2 in Nature. "If we don't understand what is created from these old stars, we don't know what the main ingredients of new stars and planets are made from."

The star the water vapor was found around is much like our star will be in 6 billion years: nearing the end of its life, expanding outward, and with more carbon than oxygen in its atmosphere. Water vapor wasn't expected around such a star, because it was thought that all the oxygen would be bound up in carbon monoxide, a stable molecule, and not available for making water molecules.

However, water vapor of unknown temperature was first discovered around this star in 2001. Astronomers proposed that the star had icy planets and comets that were vaporized as the star expanded outward. If this theory was right, the water vapor would be far away from the central core of the star, and cold.

With the launch of Herschel satellite in 2009, it was finally possible to test the theory because astronomers could collect information about the temperature of the water around the star. They found water vapor of all different temperatures around the star, which refutes the vaporized comet theory. Water could only get hot if it is closer to the star than where the comets and icy planets would have existed.

The new explanation for the water is that high energy ultraviolet light from nearby hot stars is penetrating the atmosphere of the carbon star and breaking apart the carbon monoxide molecules. Breaking these molecules apart would release oxygen that could react with the abundant hydrogen to form water.

To explain how light could get through the dense matter the star sheds off as it expands, the researchers propose that the star is less like a smooth sphere, and more like a clumpy, irregular surface.

"If the envelope is clumpy, then light which comes from outside of the star can penetrate into the envelope because there will be regions between the clumps that are more or less empty," Decin said. "When you have these photons penetrating, there is a different chemistry that takes place."

"It is a somewhat surprising explanation if it's right because in our standard understanding of these stars there is so much gas, it would block the ultraviolet radiation," said astronomer David Neufeld of John's Hopkins University, who originally discovered the water vapor around the star. "It will be interesting to see how it can be tested and what the implications are of that model being right."

Neufeld and Decin both said they have already found water vapor around other stars using the Hershel satellite, but the results have not yet been released. Neufeld said that water around carbon stars appears to be a widespread phenomenon.

Water vapor and carbon are essential building blocks of life on Earth.

"How water has arrived here on Earth is still a debate," Decin said. "And what we think now is that these ultraviolet photons were a main actor, which has been neglected until now."

Image: Hubble captured this expanding halo of light around a red supergiant star, named V838 Monocerotis/* NASA, ESA and H.E. Bond*

See Also: