The Need for a Southern Hemisphere Detector

A single gravitational wave detector, like a single human ear, is unable to tell the direction of a gravitational wave. Once the widely spaced detectors are connected (via the internet), however, it will be possible to calculate the direction of a wave from the varying arrival times of signals at each location. The addition of one southern hemisphere detector greatly improves the network.

The extra detector working with all the others increases the total sensitivity of the network, thereby raising the total number of detectable sources by 270%. It increases the directional precision of the network by even more. The graphs to the right show how a single source of gravitational waves appears with and without LIGO-Australia. Without LIGO-Australia, it appears as a huge long streak in the sky; with LIGO-Australia, its location is identified to within less than half a degree. On average, LIGO-Australia improves the directional precision of the network by 400%.

Australian scientists are already working closely with the LIGO and VIRGO teams. The southern hemisphere detector will be integrated into this collaboration and the data will be contributed to the global network for joint data analysis (see the global picture below). LIGO-Australia can be constructed economically using a new innovative design, new welding technology and with support from our overseas partners.

The west coast of Australia is the best location for a southern hemisphere detector

The west coast of Australia is the best location for the southern hemisphere detector given the current locations of the northern ones (see the contour map on the right). Advantages come from the fact that this location is roughly opposite the northern detectors, and their relative alignment is almost optimum. Thus all the detectors seethe same gravitational wave signals with roughly the same strength.

The LIGO-Australia site was contributed by the Western Australian Government. It was carefully chosen for the following reasons: easy access from the city, flatness, isolation and its pure silica sand which is ideal for seismic wave attenuation. Located in the Wallingup Plain: State Forrest 65, west of Gingin, Western Australia, the site was granted in 1998. It has been under development since 2000, with an 80m arm-length interferometer.

ACIGA established its High Optical Power Test Facility (HOPTF) at this site in 2002. LIGO has contributed key components and manpower to HOPFT, and Virgo has donated vacuum pipes. Experiments are now underway to demonstrate the technologies required to operate detectors at high optical power levels.

The Gingin site, pictured below, was carefully chosen as the optimum site for LIGO-Australia
Western Australia is the best location for the southern detector.
The improvement in angular resolution - this plot is without LIGO-Australia.
This plot is after adding LIGO-Australia - the resolution is improved significantly.
Some world network comparisons.

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