News Release

Astronomers Discover Fluoride Molecules in Interstellar Space

A team of astronomers from the United States and Germany, led by Johns Hopkins astrophysicist David Neufeld, has discovered trace amounts of hydrogen fluoride gas in the near vacuum of interstellar space, using a satellite built and launched by the European Space Agency and operated by ESA with NASA's participation. Although approximately 100 different kinds of molecules have been detected in interstellar space over the past 30 years, the discovery of hydrogen fluoride marks the first time that a molecule containing fluorine has been detected in an interstellar gas cloud. It is also the first time that a new interstellar molecule has been detected by observations at far-infrared wavelengths.

The discovery will be reported in an article that is to appear in October in the Astrophysical Journal Letters.

The astronomers searched for hydrogen fluoride molecules within a giant cloud of interstellar gas located near the center of the Milky Way galaxy, using ESA's Infrared Space Observatory satellite, which was launched in November 1995. The new observations were carried out in March 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 telltale signature of absorption by trace amounts of hydrogen fluoride gas.

"Because the Earth's atmosphere is completely opaque to far-infrared radiation, the observations that we carried out are possible only from space," said Neufeld, a professor in the Johns Hopkins Department of Physics and Astronomy. "The ISO satellite has opened up an exciting new window on the universe by allowing us to observe at far-infrared wavelengths."

In concentrated liquid form, hydrogen fluoride -- or hydrofluoric acid as it is known when dissolved in water -- is familiar to laboratory chemists as an extremely dangerous and corrosive acid that dissolves glass and severely burns human tissue. The ISO's sensitive spectrometers enabled the astronomers to detect hydrogen fluoride in interstellar space even though its concentration was less than one part per billion.

The characteristic wavelength at which hydrogen fluoride molecules absorb radiation is about one two-hundredth of an inch, much larger than the wavelength of visible light but far smaller than the wavelengths typically used for radio and television communications.

The gas cloud in which hydrogen fluoride molecules were discovered lies about 20,000 light years from Earth, in the southern constellation Sagittarius. Known to astronomers as Sagittarius B2, the gas cloud is composed primarily of hydrogen molecules. As in other clouds of interstellar gas, the environment in Sagittarius B2 is extreme by earthly standards, with temperatures less than minus 370 degrees Fahrenheit, and pressures more than one hundred trillion times smaller than the atmospheric pressure on Earth.

"This discovery gives us the opportunity to study the chemistry of fluoride molecules in the frigid conditions that characterize the near vacuum of interstellar space," Neufeld said. "One of the key questions is how these molecules were formed. Our analysis suggests that the hydrogen fluoride we detected was produced by direct chemical reactions between fluorine atoms and hydrogen molecules. Unlike most atoms, fluorine atoms are extremely reactive and attack the relatively inert hydrogen molecules that are the principal constituent of the interstellar gas. The result is hydrogen fluoride."

The other members of the team that made the hydrogen fluoride discovery are professors Jonas Zmuidzinas and Thomas Phillips of the California Institute of Technology, and Dr. Peter Schilke of the Max-Planck Institute for Radio Astronomy in Bonn, Germany. The participation of Neufeld, Zmuidzinas and Phillips as guest observers on the European satellite was supported by the National Aeronautics and Space Administration.

Further information is available from Professor Neufeld at (410) 516-8582, or by e-mail at neufeld@pha.jhu.edu. His Web address is http://www.pha.jhu.edu/~neufeld/.