• NOEL BENNY• VAJID RAHMAN K• VYSAKH A V• ABHIN KRISHNA K A• AKHIEL NAZIM K A• ALEX TOMY• AMRITHA P A• ANAGHA SUNNY

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large observatories were built in the United States with the aim of detecting gravitational waves bylaser interferometry.

LIGO Hanford Observatory

LIGO Livingston Observatory

Gravitational wave ?

Gravitational wave • In Einstein's theory of general relativity, gravity is treated as a

phenomenon resulting from the curvature of spacetime. This curvature is caused by the presence of mass. Generally, the more mass that is contained within a given volume of space, the greater the curvature of spacetime will be at the boundary of its volume. As objects with mass move around in spacetime, the curvature changes to reflect the changed locations of those objects. In certain circumstances, accelerating objects generate changes in this curvature, which propagate outwards at the speed of light in a wave-like manner. These propagating phenomena are known as gravitational waves.

Gravitational wave

LIGO• LIGO's mission is to directly observe gravitational waves

of cosmic origin. These waves were first predicted by Einstein's general theory of relativity in 1916, when the technology necessary for their detection did not yet exist. Their existence was indirectly confirmed when observations of the binary pulsar PSR 1913+16 in 1974 showed an orbital decay which matched Einstein's predictions of energy loss by gravitational radiation. The Nobel Prize in Physics 1993 was awarded to Hulse and Taylor for this discovery

After the completion of Science Run 5, initial LIGO was upgraded with certain technologies that resulted in an improved-performance configuration dubbed Enhanced LIGO. Some of the improvements in Enhanced LIGO included Increased laser power

Homodyne detection Output mode cleaner In-vacuum readout hardware Science Run 6 (S6) began in July 2009 with the enhanced

configurations on the 4 km detectors. It concluded in October 2010, and the disassembling of the original detectors began. By mid-September 2015, LIGO Scientific Collaboration included more than 900 scientists worldwide

Laser Interferometer• Interferometry makes use of the principle of superposition to

combine waves in a way that will cause the result of their combination to have some meaningful property that is diagnostic of the original state of the waves. This works because when two waves with the same frequency combine, the resulting intensity pattern is determined by the phase difference between the two waves—waves that are in phase will undergo constructive interference while waves that are out of phase will undergo destructive interference. Waves which are not completely in phase nor completely out of phase will have an intermediate intensity pattern, which can be used to determine their relative phase difference. Most interferometers use light or some other form of electromagnetic wave

Structure

Structure

Working

WorkingWhen a gravitational wave passes through the interfer-ometer, the spacetime in the local area is altered. De-pending on the source of the wave and its polarization,this results in an effective change in length of one or bothof the cavities. The effective length change between thebeams will cause the light currently in the cavity to be-come very slightly out of phase (anti phase) with the in-coming light. The cavity will therefore periodically getvery slightly out of coherence and the beams, which aretuned to destructively interfere at the detector, will havea very slight periodically varying detuning. This resultsin a measurable signal

Applications

Einstein Telescope (ET) or Einstein Observatory, is a proposed third-generation ground-based gravitational wave detector, currently under study by some institutions in the European Union. It will be able to test Einstein's general theory of relativity in strong field conditions and realize precision gravitational wave astronomy. The ET is a design study project supported by the European Commission under the Framework Programme 7 (FP7). It concerns the study and the conceptual design for a new research infrastructure in the emergent field of gravitational-waveastronomy.

Applications

LIGO-INDIAINDIGO, or IndIGO (Indian Initiative in Gravitational-wave Observations) is a consortium of Indian gravitational-wave physicists. This is an initiative to set up advanced experimental facilities for a multi-institutional observatory project in gravitational-wave astronomy. ince 2009,the IndIGO Consortium has been planning a roadmap for gravitational-wave astronomy and a phased strategy towards Indian participation in realizing a gravitational-wave observatory in the Asia-Pacific region. IndIGO is the Indian partner (along with the LIGO Laboratory in USA) in planning the LIGO-India project.