Onsala Space Observatory research
As the Swedish National Facility for Radio Astronomy, Onsala Space Observatory provides world class observing facilities for the national and international research communities in astronomy and Earth sciences. The main scientific focus is on the origins of stars and galaxies using high frequency spectroscopy and high resolution observations, and the application of these and related techniques in space geodesy and aeronomy. The full effort is supported by research and development in millimetre/submilimetre receiver technology.
The research with the Onsala telescopes is carried out by the observatory staff, and by some of the research groups at the Department of Earth and Space Sciences at Chalmers. But equally important is that the telescopes are used by other Swedish and international scientists. Access to the telescopes is granted through a review process, where the scientific merit of applications for observing time is evaluated.
Radio astronomical research spans a large area: from comets and stars to galaxies and the large-scale structure of the universe. The goal is to understand the universe and to answer fundamental questions, such as: How were the first galaxies formed and why do so many galaxies have a spiral shape? What happens close to the enormous black holes found in the centre of galaxies, even in our Milky Way? How are stars formed and what happens when stars die? How are new molecules formed in the gas clouds between the stars, molecules that may later be found on planets around other stars? How was our own solar system formed?
With radio telescopes, it is possible to observe objects that are impossible to see with an optical telescope. The centre of our Galaxy, for example, is hidden for optical telescopes by dark dust clouds, but its radio emission can be observed. Stars are formed in large clouds of dust and gas, and in such clouds more than a hundred different kinds of molecules, many of them organic, have been discovered through radio astronomy spectroscopy. Other types of radio waves are emitted from electrons moving with close to the speed of light in the magnetic fields in the neighbourhood of giant black holes.
A few examples of research projects illustrate the research with the National Facility telescopes:
Comets: Odin has detected water in 13 comets, one of them (9P/Tempel 1) the target of the NASA Deep Impact spacecraft. When the spacecraft's 370 kg impactor hit the comet at 10 km/s, Odin observed a release of about 5000 tons of water.
Star formation: The Onsala 25 m telescope has been used for a survey of methanol maser emission from the Galaxy. New sources were detected, and follow-up observations with SEST indicated that the maser sources are associated with young star formation. VLBI observations of one massive protostar revealed methanol masers in an edge-on accretion disc, showing that massive stars form by accretion of gas rather than by coalescence of smaller stars.
Evolved stars: Emission from molecules in envelopes surrounding stars in late stages of evolution is observed by radio telescopes to determine, e.g., the mass-loss rate from the stars and chemical processes in the envelopes. The mass-loss process enriches the interstellar medium, from which new stars are born, with molecules, heavy elements and grains. Many different molecular species have been observed in evolved (AGB) stars with the Onsala 20 m telescope, SEST and APEX. One important molecule is SiO, which shows evidences of non-equilibrium chemistry and adsorption onto grains.
Interstellar clouds: Different types of interstellar clouds are observed with the Onsala 20 m telescope to study, e.g., turbulence in translucent molecular clouds and chemical differentiation in dense cloud cores. An important result from Odin is the first detection ever of interstellar molecular oxygen. The abundance of interstellar molecular oxygen is, however, much lower than expected, indicating that oxygen is "locked up" as water ice on grain surfaces. With APEX new interstellar molecules has been discovered, for example hydrogen peroxide (H2O2) and CF+.
Galaxies: The distribution of molecular gas in the spiral galaxy M 51 has been mapped with the Onsala 20 m telescope, and molecular gas was detected at great distances from its centre. The properties of gas in active and starburst galaxies, observed with the Onsala 20 m telescope and SEST, was found to vary significantly among luminous galaxies in ways that can be related to starburst and AGN evolution. VLBI observations have detected obscuring molecular torii in Seyfert galaxies, and supernovas in Arp 220 indicating star formation and evolution modes in starburst galaxies radically different from standard models.
Space geodesy research in Onsala make use of VLBI and global navigation satellite systems (GNSS), e.g. GPS, to estimate the Earth's crustal movements, orientation in space, and atmospheric water vapour content. Gases in Earth's atmosphere are also observerd with radiometers, similar to those used in radio astronomy. A gravimeter continuosly measures changes in Earth's gravity caused by, e.g., tides. GPS observations of land uplift in Scandinavia (peaking at 10 mm/year) are made without the uncertainties imposed by a changing sea-level reference. The combination of GPS and tide gauge data can be used to infer changes in absolute sea-level, a key parameter in models of earth climate and ocean warming. VLBI measurements of plate tectonics started in 1980. One result is that the distance between Onsala and Westford, on the east coast of the USA, increases with 17 mm/year. The atmospheric water vapour content is measured using GPS. The information is valuable both for short term weather forcasts and for climate models.
The telescopes mentioned above are, in addition to the 20 m and 25 m telescopes in Onsala, SEST (the Swedish-ESO Submillimetre Telescope in Chile, closed in 2003), APEX (Atacama Pathfinder EXperiment in Chile, inaugurated in 2005) and Odin (a satellite for radio astronomy and aeronomy, launched in 2001). The Onsala telescopes are also used for VLBI (Very Long Baseline Interferometry). Other important facilities are the European radio telescope LOFAR and the international radioastronomical observatory ALMA in Chile.
July 26, 2011
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