LIGO-India: A Planned Joint India-US Detector

LIGO-India is a collaboration between the LIGO Laboratory (operated by Caltech and MIT) and three Institutes in India: the Raja Ramanna Center for Advanced Technology (RRCAT, in Indore), the Institute for Plasma Research (IPR in Ahmedabad), and the Inter-University Centre for Astronomy and Astrophysics (IUCAA, in Pune).

Motivations for constructing a third LIGO interferometer are primarily related to building a larger global network of gravitational wave detectors. Such a world-wide network of widely-separated facilities is needed to extract the best information from gravitational waves. Specifically, adding more detectors to the network improves our ability to locate sources, test theories of gravity, space, and time, and provide important clues to puzzles in astrophysics and cosmology.

While two detectors in a network that sense the same polarization of gravitational-waves (like Hanford and Livingston) are the minimum needed to ensure confidence that a signal is a gravitational-wave and not some terrestrial or instrumental artifact, two such detectors cannot effectively localize the source of the waves on the sky nor can they reveal a wave's actual polarization.

A network of three detectors (Hanford-Livingston-Virgo, for example) can improve the polarization information extracted from the wave and the source location. But even a three-observatory network only provides a sharp sky location for about half of all possible locations on the sky. This is illustrated in the upper figure at left.

Ultimately, the goal is to localize a source of gravitational waves anywhere in the sky. And to do this, four comparable detectors need to be operating simultaneously around the globe. Of course, given the complexity of gravitational wave detectors, to increase the odds that four detectors are running at the same time, you really need more than four in a network. Indeed, a fourth detector, Kagra, in Japan, is slated to come online in the next year. LIGO India will be the all-important fifth. When it begins operation, LIGO India will significantly improve the likelihood that four detectors are operating at any given moment. This is the critical role that LIGO India will play in the global gravitational wave detector network.

The LIGO Laboratory and India are both making significant financial and intellectual contributions to the project:

• The LIGO Laboratory is providing the hardware for a complete LIGO interferometer, technical data on its design, installation and commissioning, training and assistance with installation and commissioning, and the requirements and designs for the necessary infrastructure (including the vacuum system).
• India is providing the site, the vacuum system, and other infrastructure required to house and operate the interferometer, and all labor, materials and supplies for installation, commissioning, and operations. Funding for the LIGO-India facilities comes from the Indian Department of Atomic Energy (DAE) and the Department of Science and Technology (DST), with DAE acting as the lead agency.

Once it becomes operational, LIGO-India will be scientifically managed and operated in collaboration with the US LIGO detectors to optimize the scientific return.

Learn more by visiting the LIGO India website at www.ligo-india.in