CONDOR’s First Look at the Universe
First light of a state-of-the-art terahertz receiver at the APEX telescope in Chile
In November 2005, CONDOR, the CO N+ Deuterium Observation Receiver, opened its eye to the universe for the first time. CONDOR was installed at APEX (Atacama Pathfinder EXperiment) in the Chilean Andes and detected hot gas in the vicinity of young massive stars from radiation at the extremely high radio frequency of 1.5 terahertz (THz), i.e. 1.5 million million Hertz. The CONDOR detections are the first THz-frequency observations acquired with a large telescope (12 m diameter). The observations reveal several surprises, and the expectation that THz astronomy would yield valuable scientific results has been met. The success of CONDOR is a combined effort of researchers from the First Physical Institute of the University of Cologne and the Max Planck Institute for Radio Astronomy.
"CONDOR has fully met our expectations," said Dr. Martina Wiedner, the CONDOR project leader. "We prepared the receiver well, we had an excellent team at the site, but we also were lucky that the weather was so good." Because of the difficulty in detecting electromagnetic waves at such high frequencies (a thousand times higher than those of a cellular phone and a million times higher than "short wave" radio), state-of-the-art receivers have to be used. A special type of device called a Hot Electron Bolometer, developed at the University of Cologne by Dr. Karl Jacobs and his colleagues, was essential for CONDOR’s success. This device converts the THz frequency radiation into frequencies around 1 GHz, which are much easier to manipulate. To achieve high sensitivity, the receiver is cooled to a temperature of -269°C, only 4°C above absolute zero.
The CONDOR observations require that the amount of water vapor in the Earth atmosphere is exceptionally small, because water vapor readily absorbs THz radiation. Located in the Atacama Desert of Chile at an elevation of 5100 m, the site of the APEX telescope (see Fig. 1) is extraordinarily dry. APEX has a 12 m primary mirror that resembles a perfect paraboloid to within 15 microns (7 times thinner than a human hair). The telescope is currently equipped with receivers between 300 and 900 GHz. CONDOR, which requires different technology, is the first APEX receiver operational above 1 THz. "The CONDOR observations are done at the highest frequencies that APEX expects to ever reach," explains the APEX project manager, Dr. Rolf Güsten. "At even higher frequencies, the Earth’s atmosphere becomes opaque until one reaches the infrared wavelengths."
The CONDOR observations on APEX open up the nearly unknown THz universe for exploration. "If one could only see blue things, one would never know about trees and grass," explains Dr. Martina Wiedner. "Similarly, one discovers new things in the universe by looking at it in different frequencies. The spectral signatures of hot gas (high rotational transitions of the carbon monoxide (CO) molecule) are seen at THz frequencies. Since hot gas is an essential component of massive star formation, regions that give birth to massive stars can be observed at these frequencies." CONDOR detected emission from CO at 1.5 THz during its first observations (Fig. 2). The line width is surprisingly narrow, suggesting that the gas is heated by ultraviolet (UV) radiation from stars, rather than collisions within gases as originally expected. Astronomers on the CONDOR project team are eager to make further observations.
The CONDOR project
The CONDOR project is carried out at the First Physical Institute of the University of Cologne (I. Physikalisches Institut of the Universität zu Köln) in an Independent Junior Research Group of the Collaborative Research Center 494 (Nachwuchsgruppe im Sonderforschungsbereich (SFB) 494). About 100 scientists from Germany are working in this Collaborative Research Center, entitled "The Evolution of Interstellar Matter: Terahertz Spectroscopy in Space and in the Laboratory." The APEX telescope was built jointly by the Max Planck Institute for Radio Astronomy in Bonn, Germany, the Onsala Space Observatory, Sweden, and the European Southern Observatory.