Astronomers have discovered an interstellar gas cloud bloated with enough water vapor to fill all the Earth's oceans at least 1 million times.
The finding confirms calculations made by a former Johns Hopkins graduate student, whose precise predictions supported previous theories that water is formed as young stars heat up surrounding space, causing chemical reactions that unite oxygen and hydrogen.
Astronomers believe that water is a key ingredient in star formation. It apparently is needed to cool off gases before they can collapse to form stars and planets.
The discovery was made by a team of U.S. astronomers using the Infrared Space Observatory satellite, launched and operated by the European Space Agency. Michael Kaufman, who received his doctorate here in 1995, was a member of the team reporting the finding, as was David Neufeld, a professor in the Department of Physics and Astronomy. The discovery is detailed in an article being published this week in the Astrophysical Journal Letters.
The astronomers found a large concentration of water vapor within the cloud of gas, located about 1,500 light-years from Earth near the Orion nebula, a huge glowing cloud of gas and dust in the center of the constellation Orion. The water concentration is 20 times greater than that measured previously in other interstellar gas clouds, a finding that may provide an important clue to the origin of water in the solar system.
"The interstellar gas cloud that we observed in Orion seems to be a huge chemical factory, generating enough water molecules in a single day to fill the Earth's oceans 60 times over," said Neufeld.
"Eventually that water vapor will cool and freeze, turning into small solid particles of ice," he said. "Similar ice particles were presumably present within the gas cloud from which the solar system originally formed. It seems quite plausible that much of the water in the solar system was originally produced in a giant water vapor factory like the one we have observed in Orion."
The total amount of water detected would fill the Earth's oceans about 1 million times. Moreover, scientists suspect that the cloud may contain 50 times more water than the amount actually detected, he said.
Astronomers found the water within the Orion Molecular Cloud, a giant interstellar gas cloud composed primarily of hydrogen molecules.
Before the satellite was launched, in 1995, astronomers knew little about the concentrations of water in deep space.
"The Earth's atmosphere is just so full of water that it severely interferes with any observations that you want to make," Neufeld said. "ISO discovered it in many different places, such as interstellar regions where stars are forming, dying stars and planets and moons within the solar system."
The new observations were carried out in October 1997 with the Long Wavelength Spectrometer, one of four instruments on board ISO. Looking in the far-infrared region of the electromagnetic spectrum, the astronomers observed the characteristic signature of water vapor.
"We observed a high concentration of water near the birthplace of a newly formed star in Orion," Neufeld said. "As new stars are born, material is thrown out at high speed into the parent interstellar cloud, creating shock waves that heat and compress the gas. The warm water vapor that we observed is produced behind those shock waves."
Astronomers believe that shock waves may be a cause as well as a result of star birth. "In the future, they may also trigger the formation of additional stars and planets as they compress the gas cloud that we observed, but only if surplus heat can be radiated away," said Martin Harwit, a professor at Cornell University who is an ISO mission scientist and lead author on the paper that reported the discovery.
"Even though the interstellar gas is composed primarily of hydrogen molecules, water vapor is a particularly efficient radiator at far-infrared wavelengths and plays a critical role in cooling the gas and facilitating the star formation process," Harwit said.
The concentration of water vapor measured by the U.S. team was roughly one part in 2,000 by volume, some 20 times larger than that measured previously in other interstellar gas clouds.
"An enhanced concentration of water is precisely what we expected in this gas cloud," said team member Gary Melnick, of the Harvard-Smithsonian Center for Astrophysics. "We are looking at a region of interstellar space where shock waves have made the gas abnormally warm. For the past 25 years, astrophysicists have been predicting that whenever the temperature exceeds about 200 degrees Fahrenheit, chemical reactions will convert most of the oxygen atoms in the interstellar gas into water. And that's exactly what we've observed in Orion."
The strength of the water radiation detected from Orion matched the theoretical predictions published in the doctoral thesis of team member Michael Kaufman, who is now an astrophysicist at NASA's Ames Research Center, in Mountain View, Calif.
"There had been earlier models that had predicted there would be a lot of water," said Neufeld. But none of those models made specific predictions about the strength of the infrared radiation released from the water, which reveals important details about properties of the interstellar cloud.
An image of the signature of water and an image of the Orion nebula can be found on the Web at www.pha.jhu.edu/~neufeld/orionwater.html