HIFI’s quest for water sheds new light on the birth of stars in different regions of the Universe. This much became clear at The First Results Symposium of the Herschel space telecope, with onboard the Dutch space instrument HIFI. With HIFI scientist discovered ionised water for the first time in space. These electrically charged water molecules do not exist on Earth.
The role of water is crucial in the processes of star formation, because this molecule contributes to the cooling of the gas and dust mixture from which stars are born. Early results, reported this week at the Herschel First Results Symposium, demonstrate the detection of water in various proto-stellar systems. Along with upcoming data from star-forming clouds throughout the Milky Way, these data will help astronomers understand the mechanisms of star formation in great detail.
The presence of water in a celestial object is revealed through its very distinctive fingerprints, or lines, in the object’s spectrum at far-infrared and sub-millimetre wavelengths. Only high resolution spectrographs, such as HIFI on board ESA’s Herschel Space Observatory, are able to obtain spectra sufficiently precise to track down the abundance of water in great detail.
HIFI, or the Heterodyne Instrument for the Far Infrared, was designed with the quest of water and other molecules very much in mind. Based on the heterodyne detection principle, it basically translates, without loss of information, the high-frequency signal received from astronomical sources to a lower frequency, where measurements are easier to perform. “With its superb spectral resolution HIFI is ideally suited to detect and characterize molecular lines. It is an excellent molecule hunter, even better than we had hoped,” says Frank Helmich, Herschel-HIFI Principal Investigator.
“Water is an excellent diagnostic tool to probe the chemical and physical structure of the interstellar medium,” explains Alexander Tielens from Leiden University. “Early detection of this important molecule on all cosmic scales highlights that HIFI is working extremely well.”
With its superb resolution, HIFI can target about 40 different lines, each coming from a different transition of the water molecule and thus sensitive to a different temperature. Except ordianry water molecules Herschel/HIFI also found ionized water. These water molecules are electrically charged because irradiation knocks out an electron. Ionizez water does not occur naturally on Earth. "The discovery of ionized water vapour came as a surprise," says Ewine van Dishoeck, Leiden University. "It tells us that there are violent processes taking place during the early birth stages which lead to widespread energetic radation throughout the cloud."
Water trails go all the way from vast star-forming clouds down to stars and planets on much smaller scales. In the proto-planetary discs surrounding stars in the process of forming, water vapour may in fact freeze onto dust grains; these cold grains would then condense into icy planetesimals, the seeds of planet formation.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia, with important participation from NASA. HIFI, a high resolution spectrometer was designed and built by a nationally-funded consortium led by SRON Netherlands Institute for Space Research. The consortium includes institutes from France, Germany, USA, Canada, Ireland, Italy, Poland, Russia, Spain, Sweden, Switzerland, and Taiwan.
The distribution of water and its related species is the primary focus of the Key Programme WISH: Water In Star-forming regions with Herschel, led by Principal Investigator E.F. van Dishoeck. This programme is dedicated to studying the physical and chemical structure of star-forming regions through combined HIFI and PACS spectroscopy.
The Herschel First Results Symposium, ESLAB 2010, is taking place this week at ESA’s Space Research and Technology Centre, ESTEC, in the Netherlands.