First step towards Interferometric Gravitational Wave Observatory

Indian gravitational astronomy research got a major boost on September 14 with the approval of the Tata Institute of Fundamental Research (TIFR) to fund a Rs.2-crore proposal for building a prototype gravitational wave (GW) detector.

This three-metre-long optical interferometer-based detector is the first step in the four-phase strategy recommended by a consortium of Indian gravitational astronomy researchers towards building a four-km class Indian Interferometric Gravitational Wave Observatory (IndIGO) by the year 2020.

The building of the prototype, led by C.S. Unnikrishnan and G. Rajalakshmi of the TIFR, is expected to be completed in three years.

Major challenge

Direct detection of GWs, which Einstein's theory of gravitation predicts, has been a major challenge for physics, and at present there is only indirect evidence for their existence (see photo). Gravitational waves are ripples in spacetime — somewhat like propagating ripples on the surface of a pond — caused by the acceleration of a gravitating body.

As these distortions of spacetime travel outward, they cause changes in the lengths of objects in their path, which are different in different directions with respect to the wave direction. The idea is to pick up these signatures with instruments on the Earth as the passing waves affect different parts of the apparatus differently.

But being a feeble interaction, these length changes on the Earth are extremely small — about a hundredth of a billionth of a billionth of a metre — and only phenomena involving highly massive objects can produce signatures that may be detectable on the Earth.

Instruments based on laser interferometry — with reflecting mirrors suspended in ultra high vacuum conditions and separated by large distances to increase the signal strength — promise to give the best sensitivity. But detecting GWs even from violent astrophysical systems has proved to be extremely difficult after decades of effort. However, with vast improvements in technology, current detectors have successfully attained design sensitivity close to the detection threshold.

Worldwide network

There is a strong international effort under way to build a worldwide network of ground-based detectors capable of opening the field, as the existing network falls well short of all-sky coverage. One of the main objectives of the Gravitational Waves International Committee (GWIC) is to optimise global research in GW astronomy with a 30-year horizon.

The GWIC's first priority is to expand the network with appropriately chosen international baselines and orientations to maximise the detection capability. A recent report of the GWIC recognises the need for a detector in the Asia-Pacific region — Australia, Japan, and possibly India or China.

In June, the GWIC noted its appreciation of the long-standing GW research activity in India in theory and data analysis, and endorsed the multi-pronged strategy proposed by the consortium to initiate experimental work as well.

The IndIGO consortium comprises 26 scientists that include researchers drawn from nine leading Indian institutions, as well as Indian scientists who are actively engaged in the field at major gravitational astronomy research centres of the world such as the Laser Interferometer Gravitational-wave Observatory (LIGO) at Caltech, United States, and the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Potsdam, Germany.

The consortium, chaired by Bala Iyer of the Raman Research Institute, Bangalore, had submitted its detailed proposal and a road map for IndIGO to the directors of institutions with possible interest in GW astronomy and to leaders of the Indian scientific community on December 4, 2009.

MoU between consortiums

Another important step in this phased strategy that will be formalised very soon is the signing of a Memorandum of Understanding (MoU) between the IndIGO consortium and the Australian Consortium for Interferometric Gravitational Astronomy (ACIGA).

The ACIGA, established in 1995, coordinates gravitational research in Australia and is a collaboration of five leading Australian universities. It operates a national research facility called the High Optical Power Facility (HOPF) at Gingin, located on a 50 sq.km. site about 80 km north of Perth.

One of the chief objectives of ACIGA is to build the Australian International Gravitational Observatory (AIGO) with an advanced GW detector at this site. It is already an active participant in the LIGO Scientific Collaboration (LSC) and a partner in the Advanced LIGO project, which is constructing three four-km baseline laser interferometric GW detectors.

Recently, the National Science Foundation (NSF) of the U.S. approved the proposal to construct one of these LIGO detectors at the AIGO site if Australia can raise funds to the tune of $170 million to build the infrastructure (including vacuum systems), provide staff, and meet the operational costs over 10 years.

The ACIGA, in turn, seeks to form an international collaboration, including the U.S., Germany, the U.K., India, China, France and Italy.

Indian participation

The ACIGA-IndIGO MoU will enable Indian participation in the setting up of AIGO and associated research in advanced detector technology, which is expected to give Indian researchers experience in state-of-the-art optical, mechanical and quantum metrology techniques towards building IndIGO, a third generation GW detector.

The MoU will also link IndIGO with the international programme of ground-based GW detection through access to all data generated through the LSC. The MoU will remain in effect for three years subject to a mid-term review in December 2011 and the total amount of funding envisaged towards this collaboration is about Rs.125 crore, most of which is expected to be spent in fabrication of sub-systems and tests in India.