September 2, 2010
Herschel Finds Old Star Surrounded By Water
CW Leonis, a star some 500 light-years from Earth, has become a recent hot topic for scientists, who have long known it to be surrounded by a shroud of water.
The star, twice as massive as our Sun, has been looked on by Europe's Herschel space telescope as an old giant star wallowing in a "Ësteam bath'.
"Herschel really is the most amazing water detector," lead researchers Dr Leen Decin from Katholieke Universiteit Leuven, Belgium, told BBC News.
The gigantic cloud of water surrounding CW Leonis was first detected in 2001 by the Sub-millimeter Wave Astronomy Satellite (SWAS). Scientists first believed the water originated from comets, or even planets, that had been annihilated by the giant star.
The idea that water could have been produced around the star itself didn't seem plausible because CW Leonis had reached a stage in its life when its nuclear core was producing colossal amounts of carbon.
The "sooty exhaust" would have been expected to take up any free oxygen in the area of the star to make carbon monoxide.
But instruments -- PACS and SPIRE -- aboard Herschel have a great sensitivity to water, seeing it in many different states. The spectrometers were able to confirm that the star's water was present very close in to the star, all the way down to near the surface -- far too close to come from comets.
Scientists working on Herschel propose that a previously unsuspected chemical process is at work. Ultraviolet light from nearby bright, hot stars is breaking up the carbon monoxide and releasing its oxygen atoms to join up with hydrogen and form water molecules.
Such a chemical process should normally be blocked, especially in an aged star such as CW Leonis. The UV light should be prevented from getting through to the carbon monoxide to work on it.
But Herschel, as well as other telescopes, has shown the stellar wind billowing away from CW Leonis to be very clumpy, allowing UV light to penetrate deep in towards the star and trigger water production.
"This is really exciting, since it is the first time that we have seen a lot of carbon and water molecules co-existing close to a very luminous, but dying, star," said Dr Decin.
"Carbon and water are two of the major the building blocks for life as we know it on Earth. The same mechanisms triggered by ultraviolet light might have played a crucial role in prebiotic processes on the early Earth," he told BBC.
Herschel carries the largest mirror ever sent into space, measuring nearly 11.5 feet. Its instruments are sensitive to light and long wavelengths in the far-infrared and sub-millimeter range.
By being above the Earth's water-filled atmosphere, Herschel is able to study the molecule's prominence elsewhere in the Universe.
Image Caption: This Herschel image shows IRC+10216, also known as CW Leonis -- a star rich in carbon where astronomers were surprised to find water. This color-coded image shows the star, surrounded by a clumpy envelope of dust, at three infrared wavelengths, taken by Herschel's spectral and photometric imaging receiver (SPIRE) and photodetector array camera and spectrometer (PACS). Blue shows light of 160 microns; green shows 250 microns; and red shows 350 microns. Credit: ESA/PACS/SPIRE/ Consortia
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