When the present upgrade is complete, the Sydney University Stellar Interferometer (SUSI) will be able to resolve objects the size of a beach ball on the Moon, says Mike Ireland of Macquarie University in Sydney. This large interferometer will be used to determine the dimensions—size, weight and velocity—of pulsating stars, hot stars, and massive stars. SUSI will also be involved in the search for binary stars and their planetary companions.
Built at CSIRO’s Paul Wild Observatory near Narrabri in northern New South Wales in the late 1980s, SUSI began operating in 1991. By analysing the interference patterns generated by combining light detected using charge-coupled devices (CCDs—the heart of a digital camera), this interferometer can simulate the performance of an optical telescope with a lens diameter of up to 160 metres. The only drawback is that it can detect only the brightest celestial bodies because it uses such small apertures.
The upgrade involves installing two new devices—PAVO (Precision Astronomical Visible Observations) and MUSCA (Micro-arc second University of Sydney Companion Astrometry)—which combine the beams in different ways to make measurements. The PAVO technology, software and cameras have already been attached to an even bigger interferometer, called CHARA, on Mount Wilson in California. Both instruments can be controlled remotely over the internet from Sydney, and are the highest spatial resolution instruments operating using visible light in the Northern and Southern skies.
MUSCA can measure the separation between binary stars precisely, and determine if they are moving sideways with respect to one another. In this way, the gravitational tug of an unseen planetary companion can be detected.