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Telescopes and space missions

Telescopes and space missions

Quasar images confirm potential of virtual telescopes

18 Sep 1998

Radio astronomers have created a 'virtual' radio telescope with a dish size greater than the diameter of the Earth. The technique of very long baseline interferometry (VLBI) has been used to combine signals from 40 ground-based radio telescopes and the 8-metre HALCA telescope in space. The VLBI space observatory project (VSOP) has now released some of the best images of quasars ever seen (Science 281 1825).

HALCA was launched by Japanese astronomers in 1997 to detect radio signals at wavelengths that that are difficult to detect from the ground. In addition to conducting their own observations, the HALCA team have co-ordinated a series of observations with ground-based telescopes to produce enhanced images of quasars. These immensely energetic and distant objects are thought to be powered by supermassive black holes that consume gas and stars from surrounding galaxies. The VSOP images include unprecedented detail of jets of material close to the quasar’s core. They reveal complex jet-like structures which suggest that the material powering the quasars suffers from magnetic instabilities associated with a spinning black hole.

“The new observations with HALCA are scientifically important in themselves”, according to Martin Hardcastle, a radio astronomer at Bristol University in the UK, “since they probe active galactic nuclei with a combination of physical size and frequency that has not been accessible until now. They also represent an important proof that orbiting VLBI can work and produce science that complements existing ground-based arrays.”

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