29 November 1999

Edited by Emma Sanders

Galileo telescope

Galileo, the new 3.5 m Italian national telescope, will soon be open to astronomers. Situated on the Roque de los Muchachos Observatory in the Canary Islands at an altitude of 2400 m, its prestigious neighbours include the UK­Dutch Isaac Newton telescopes and the Nordic Optical telescope. Galileo saw first light in 1998. Operational problems with its controls are now resolved.

VIRGO advances at Pisa

When Galileo dropped cannon balls from the top of the leaning tower of Pisa early in the 17th century, he demonstrated that all bodies fall with equal acceleration. It is fitting, therefore, that Pisa will be the home of a remarkable new gravity experiment ­ VIRGO.

Einstein predicted the existence of gravitational waves, which are generated by perturbations in space­time. Examples of strong sources of gravitational waves include supernova explosions, binary star systems, interacting black holes and even the Big Bang. The weakness of the force of gravity makes it extremely difficult to detect gravitational waves. Astronomers only have indirect proof of their existence from observations of orbiting neutron stars.

VIRGO will attempt to make direct measurements of these gravitational waves. The experiment will consist of a laser interferometer with two 3 km perpendicular arms. As gravitational waves distort space­time along perpendicular directions, the waves will either lengthen or shorten the arms of the interferometer and this will show up when the laser beams are recombined.

Incredible accuracy is required; VIRGO will use the first of a new generation of ultrastable lasers and the mirror surfaces will be accurate to one hundredth of a micrometre. The mirrors will be suspended on a system of five pendula to eliminate seismic noise.

VIRGO is a collaboration between France and Italy. The facility is due to open in 2001. A similar project, called LIGO, is being built in the US, and other groups are working on cryogenic resonant bar detectors for gravitational waves (CERN Courier March).

Double vision aids high resolution

The largest telescope in the northern hemisphere will be the Large Binocular Telescope (an optical infrared interferometer) at Mount Graham in Arizona. It will have two 8.4 m primary mirrors (mounted on the same support structure), which will give a light-collecting area equivalent to that of a 12 m telescope. The design is different from other large telescopes and astronomers are looking forward to interesting high-resolution studies.

The European Southern Observatories’ Very Large Telescope (VLT) is an interferometer with four telescopes (CERN Courier April). Its resolution will be 5 times as great as that of the Large Binocular Telescope (LBT). However, more signal will be lost through the complicated VLT optics, so the LBT will be able to observe much fainter objects.

The mechanical structures of both telescopes are being built in Italy by Ansaldo. The US and Germany are collaborating in the LBT project. Commissioning should finish by 2003.

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