In 'Nursery' for Stars, It's a Watery World
Scientists' findings reveal the significance of water - and lots of it - in turning gas clouds into stars.
A nascent sun 1,500 light-years away has turned its neighborhood into the most water-rich stellar nursery astronomers have ever seen.
Located in the constellation Orion, this celestial wellspring produces enough water each day to fill 60 Earth-like oceans. It contains 20 times more water vapor than any interstellar gas cloud yet observed.
The region may hold clues to the origins of water - and thus the rise of life - in our solar system, say the astronomers who took the measurements. Moreover, it hints at the key role water vapor may play in nurturing embryonic stars, which one day could warm water-laden planets of their own.
"We're beings that thrive on water, and we see water populating the heavens. This is a big piece of the puzzle in how we got here," says Gary Melnik, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
The center of attention is a still-forming star that lies within a trillion-mile-wide molecular cloud in Orion's sword. When stars form, their gravity draws hydrogen and other material in from their surroundings. But these protostars also eject about a third of that material back into space, says Michael Kaufman, an astrophysicist at the National Aeronautics and Space Administration's Ames Research Center near Mountain View, Calif. As dust and gas hurtle outward at hundreds of miles a second, they slam into the surrounding gas. This "collision" forms shock waves, which compress and heat the ejected matter. When the temperature in the shock waves reaches 100 degrees Celsius, oxygen atoms bind with hydrogen molecules and - voil - water is formed.
"When I was a babe in arms, people who studied the chemistry of interstellar clouds said that this was likely to happen," Dr. Kaufman says. It became his task, while a graduate student at The Johns Hopkins University in Baltimore, to come up with a detailed model of the chemical reaction. He and David Neufeld, a professor of astronomy and physics at Johns Hopkins, published their results in 1996. Then they joined forces with Dr. Melnik and astrophysicist Martin Harwit to see if their model's water-production estimates matched what was happening in nature.
"It was a very difficult prediction to test," Melnik says.
Ground-based telescopes - the usual method of collecting information - were useless: The signature from water vapor in Earth's atmosphere would swamp the signal coming from 1,500 light-years away.
So last October, the team used an "eye" in orbit. They aimed a spectrometer aboard the Infrared Space Observatory at the area, known as the Orion BN-KL region, and detected water's unique signatures.
"We feel quite jubilant about finding them," says Dr. Harwit, a Cornell University professor emeritus.
The researchers offer two reasons for the large amount of water they found.
They begin with water's basic ingredients, hydrogen and oxygen. Hydrogen molecules make up 90 percent of the interstellar cloud. Under assault from shock waves, oxygen atoms get stripped from nearly every compound they inhabit. With energy from the shock wave's heat, plenty of hydrogen and plenty of available oxygen atoms yield an ocean's worth of water every 24 minutes. In addition, the region they studied is part of a cloud that is a hotbed of star formation, and thus water formation.
Indeed, water vapor may be stimulating star formation, the researchers say.
When a star forms, it begins as a pocket of gas with a higher density than its surroundings, Harwit explains. But unless the hot, dense area can be cooled relatively quickly, it will expand again.
Water vapor, which radiates heat efficiently, thus may cool a pocket of dense gas, allowing it to survive continued pounding and compression until it becomes sufficiently dense for gravity to keep it from rebounding.
"Water is very much an enabler of the birth of stars," Melnik says.