Laboratory for Terahertz Science -- Astronomy

Astronomical context: Terahertz frequencies correspond to the transition between the infrared and radio portions of the electromagnetic spectrum. At shorter wavelengths (visible and near-infrared) bulk photon detection techniques -- beginning with photography and advancing to area electronic semi-conductor detectors in more recent years -- have provided astronomers with sensitive access to the universe using large ground-based telescopes. At the longest wavelengths -- the radio portion of the spectrum -- heterodyne techniques have provided similar capability to analyze faint astronomical sources. Technology advancements have recently extended heterodyne capabilities to frequencies of 1,000,000 megahertz (one terahertz) and higher.

Astronomical applications: Opening new regions of the electromagnetic spectrum has been one traditional avenue for assured new discovery in astronomy. The terahertz region of the spectrum is largely unexplored due to technological limitations and the lack of transparency of the Earth's atmosphere over a broad part of the terahertz regime. The technological limitations are being addressed by research ongoing in Charlottesville. The Earth's atmosphere is transparent over some regions of the terahertz spectrum and the atmospheric absorption can be circumvented entirely by observing on aircraft or in space.

Heinrich Hertz Telescope: Currently in operation on Mt. Graham, this telescope provides a ground-based capability to exploit terahertz receivers for astronomical research. The University of Virginia has recently entered into a partnership with the University of Arizona which provides UVa access to this facility. The surface accuracy of the dish and limitations of the Earth's atmosphere would focus the utility of this telescope on the 0.3-2 THz range.
The Stratospheric Observatory for Infrared Astronomy: SOFIA will become operational in 2005 and is a flying observatory containing a 2.5-meter telescope. Water vapor makes the Earth's atmosphere opaque over a substantial fraction of the Terahertz range. By flying in the stratosphere SOFIA provides a transparent view of space across the Terahertz regime. NASA generously funds instrument development for this observatory and it is an ideal platform for student training due to the modest size of the telescope and associated instrumentation.
Mid-infrared heterodyne spectroscopy with existing large telescopes (e.g. the Large Binocular Telescope): Within 10 years heterodyne systems operating at 15 THz will permit routine high resolution spectroscopy at wavelengths where the Earth's atmosphere is transparent (particularly at 10 and 20 micrometers). We can anticipate that leadership in the development of such systems can emanate from Charlottesville. Existing and proposed "optical" telescopes will be one natural platform for these systems.
The Large Millimeter Telescope: Slated for completion in 2005, this telescope will operate just below 1 THz. Its 50-meter collecting aperture renders it uniquely sensitive to extended sources of emission, making it an ideal platform for cosmological and extragalactic studies.
The Large Atacama Telescope project (2015): Cornell University, in collaboration with the University of Texas, U. Va., and other institutions has been developing a concept for a 15-20m diameter telescope designed specifically for the mid-infrared terahertz regime. The telescope would be sited in the Atacama desert adjacent to the NRAO ALMA installation. Most telescopes cater to interest across a broad range of the electromagnetic spectrum. One dedicated to and optimized for a more narrow range of poorly explored wavelengths has the potential for significant discovery.
The Atacama Large Millimeter Array: The National Radio Astronomy Observatory (NRAO), headquartered in Charlottesville, is leading the development of the $300M ALMA project. This array of 64 telescopes will provide unprecedented sensitivity and spatial resolution at frequencies up to 1 THz.
NASA Small and Mid-class Explorer Opportunities (ongoing): NASA is committed to providing frequent access to space for modest sized ($100 -$300 million) experiments. Approximately two such missions fly each year. Due to the opacity of the Earth's atmosphere, such missions are ideal platforms for terahertz studies.


Terahertz Astronomical Science

Cosmology: The cosmic microwave background radiation, arising from the epoch of recombination 300,000 years after the Universe began, peaks at wavelengths just longward of 1 THz. Observations of the structure of the background radiation are diagnostic of conditions which prevailed when the universe was young. This nascent structure, via gravitational amplification, has imprinted imprinted itself upon the present-day distribution of galaxies in the present-day universe. In addition, as we look out into space we literally look back in time. The most distant objects we can observe directly reveal conditions when the Universe was young. Analysis of nearby galaxies suggests that the primary diagnostics of galaxies as they were first forming in our Universe will be obtained at terahertz wavelengths.
Star and Planet Formation: The Terahertz regime provides unique access to the processes around forming stars. Both molecular line emission and thermal continuum from circumstellar disks are diagnostic of how these structures relate to the formation of planets. The terahertz radiation properties of small dust grains and macromolecules is of interest in determining the mass, structure, and temperature of these planet-forming disks. Laboratory measurement of grain/molecular properties naturally link astronomy, physics, chemistry, and material science.
Molecular Clouds: Integral to the process of star and planet formation is the raw material from which these objects form -- Molecular Clouds. These objects are both dynamically and physically cold and can only be probed in detail at Terahertz wavelengths and longward. Laboratory measurement of the wavelengths of molecular spectral lines is of particular value in interpreting such results and provides a natural link between Chemistry and Astronomy.
The Physics of the Interstellar Medium: On larger scales, diffuse gas and dust permeates our Milky Way galaxy forming one key element of the recycling system that transforms diffuse material into stars and then returns that material into interstellar space. Key coolants of this material are emission lines of oxygen and carbon which lie in the Terahertz range.
Planetary Atmospheres: Atmospheres are rich in molecules which emit and absorb at terahertz wavelengths. Observations are diagnostic of the vertical temperature and compositional of the atmospheres. The high density of these atmospheres (relative to interstellar environments) provides direct opportunity for laboratory simulation.