Building the world’s biggest telescope
The practice of radioastronomy is finally being brought up to speed with current technologies. Radio telescopes across the globe are being linked together in a network to deliver new standards of quality of data. Plans for the most powerful radio telescope on Earth are also in development.
The Westerbork synthesis radio telescope, also called Westerbork array, is a 2.7km long line of 14 large antenna dishes in north-eastern Holland. This array is part of the global radio astronomy network, which uses the technique of Very Long Baseline Interferometry (VLBI). VLBI involves sending signals from radio telescopes around the world to a central computer, or correlator, where the signals are combined to generate one single image. Since the signals are measured over a much larger distance, the distance between the telescopes, the accuracy of the resultant image is increased by several orders of magnitude. The quality of the image is therefore proportional to the distance between participating telescopes.
20 km from the Westerbork array is the Joint Institute for VLBI in Europe (JIVE). Traditionally, the data from other telescopes were sent to JIVE on magnetic tapes or hard drives. It would normally take weeks for the data to arrive, then more weeks before the scientists gained access to their data. To put an end to such delays, telescopes across the world are being linked with the JIVE correlator using optical fibre cables. JIVE and the European VLBI Network have spend the last few years creating real-time connections between telescopes and the correlator at JIVE, giving astronomers direct access to the most important data sources. They can now receive high-resolution images of distant objects and react quickly to any sudden changes in space.
The Lovell telescope is a 76-metre dish at the Jodrell Bank Observatory, near Manchester, and the third largest steerable antenna in the world. It plays an important role in international observations and is now connected to the JIVE correlator. Although the network will deliver detailed pictures of galaxies, regions around massive black holes, and regions of forming stars, the director for Jodrell Bank's Centre for Astrophysics, Phil Diamond, explains that a real-time global network will not be sufficient in the near future. "Massive sensitivity" is required to be able to observe more objects and try to "understand the physics of how stars form, how black holes form". This has led to plans for the Square Kilometre Array.
The Square Kilometre Array will have a collecting area 100 times larger than that of the Lovell telescope. The array is jointly funded by Europe and planned to be built by 2020 in either a Southern African or an Australian desert. Current plans visualise the Square Kilometre Array as a five kilometre circle filled with 15 metre dishes. Within the central one kilometre is a much higher concentration of dishes - about 25% of the total array. At the very centre is a circle of flat panels functioning as static telescopes. All components are naturally linked electronically with further remote stations extending outwards in the form of spiral arms. Since the detail of the data depends on the separation between the remote stations, the array simulates a single telescope three or four thousand kilometres across, capable of observing the whole visible sky.
Following the flow of high accuracy data from the European network, the mammoth undertaking of the Square Kilometre Array should promise a new era for radio astronomy.