LIGO experiment and LIGO-India

Three American physicists Rainer Weiss, Kip Thorne and Barry Barish won the Nobel Prize for their contribution towards Laser Interferometer Gravitational-Wave Observatory, or LIGO, experiment. The experiment involved more than 1000 scientists from across the world. Weiss was awarded one-half of the $1.1 million Swedish kroner prize, Thorne and Barish will split the second half.

About LIGO (Laser Interferometer Gravitational wave Observatory)

It is a large scale physics experiment observatory established in 2002 to detect gravitational waves. Our telescopes could detect objects which emit electromagnetic radiations like X-ray, gamma rays etc. However, merger of black holes and many other cataclysmic events do not emit electromagnetic waves rather gravitational waves. Thus, LIGO was established to unfold the many unknown phenomenon in universe through the gravitational waves detection.

It was launched as a joint project between MIT, Caltech and other universities. Currently LIGO operates three gravitational wave detectors-One is at Livingston in Louisiana and other two are at Hanford in Washington and the detectors are located about 3,000 km apart in L shape. The overall project is funded by National science foundation.

What is interferometer used in LIGO?

Interferometers are investigative tools used in many fields of science and engineering. They are called interferometers because they work by merging two or more sources of light to create an interference pattern, which can be measured and analyzed and hence “Interfere-ometer”.

The interference patterns generated by interferometers contain information about the object or phenomenon being studied. They are often used to make very small measurements that are not achievable any other way. They are so powerful for detecting gravitational waves-LIGO’s interferometers are designed to measure a distance 1/10,000th the width of a proton!

What are gravitational waves?

Albert Einstein also predicted gravitational waves in 1916 in his general theory of relativity a century ago.

Gravitational waves are ‘ripples’ in the fabric of space-time. It can be explained by taking an analogy. For instance- If you drag your hand through a still pool of water, you’ll notice that waves follow in its path, and spread outward through the pool. Similarly, when objects with mass accelerate, such as pair of merging black holes, by supernovas or neutron star binaries spiraling around each other etc. they send waves in space-time around them at speed of light, just like ripples in a pond. These are called as gravitational waves. They are extremely weak so are very difficult to detect. More massive the object, the larger the wave and the easier for scientists to detect.

In 2015, first historic observation of gravitational waves was observed  triggered by the violent merger of two black holes a billion light years away. Since then four gravitational waves have been detected.

Utility of gravitational waves

Unlike light waves, the gravitational waves do not interact with the matter, therefore they do not get distorted and gives us pure information about the the objects and events that created them million years ago. Thus, this property help us seeing back in time and can give us massive insights about a lot of processes going on in the universe ranging from origin of universe to studying black holes and mapping frequency of their mergers, dark matter etc.

India’s Contribution toward the LIGO experiment

The Indian scientific community has made seminal contributions to gravitational-wave physics over the last couple of decades through their research papers and other contributions supplementing the foundation of gravitational wave experiment.

Indian participation in the LIGO Scientific Collaboration, was done under the umbrella Initiative –IndIGO, which is a consortium of Indian gravitational-wave physicists. Bala Iyer of the Raman Research Institute has made immense contribution towards setting up of this consortium. Apart from other institutes, the three lead institutions in the IndIGO consortium are: Institute of Plasma Research (IPR), Inter-University Centre for Astronomy and Astrophysics (IUCAA), and Raja Ramanna Centre for Advanced Technology (RRCAT).Its long term aim was to develop an LIGO-India gravitational-wave observatory, thereby, building a network of gravitational wave detectors worldwide. The network includes the two LIGO detectors in the US (in Hanford and Livingston), the Virgo in Italy, and the proposed KAGRA detector in Japan.

The consortium especially under Bala Iyer facilitated international collaborations in gravitational-wave- physics and astronomy and initiating a strong experimental gravitational-wave research program in India.

Other parallel contributions include:

• The original discovery paper published had the name 39 Indian authors/scientists from nine institutions-, CMI Chennai, ICTS-TIFR Bengaluru, IISER-Kolkata, IISER-Trivandrum, IIT Gandhinagar, IPR Gandhinagar, IUCAA Pune, RRCAT Indore and TIFR Mumbai.
• The group at Bangalore led by B.R. Iyer (currently at International Centre for Theoretical Sciences (ICTS)-TIFR) in collaboration with a group of French scientists pioneered the theoretical calculations used to model gravitational-wave signals from orbiting black holes. Theoretical work that combined black holes and gravitational waves was published by C. V. Vishveshwara in 1970. These contributions are prominently cited in the discovery paper.
• The ICTS-TIFR group made significant, direct contributions in obtaining estimates of the mass and spin of the final black hole, and the energy and peak power radiated in gravitational waves. The group has also contributed to the astrophysical interpretation of the binary black hole merger. The ICTS-TIFR group designed and implemented one of the tests of general relativity that have shown that the current observation is completely consistent with a binary black hole collision in Einstein’s theory.

What is LIGO-India?

The formation of LIGO-India observatory was announced soon after the confirmation of first gravitational waves in 2016 and is expected to be commissioned by 2024. LIGO-India project will be a mega science project to be jointly funded by the Department of Atomic Energy (DAE) and the Department of Science & Technology (DST).

LIGO-India project aims to move one Advanced LIGO detector from Hanford (US) to India. It will be an international collaboration between LIGO Laboratory and three Indian institutions-Institute of Plasma Research (IPR) Gandhinagar, Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune and Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. It will be a part of a global network of LIGO observatories.

Primary reason for establishing LIGO India is that the two existing detectors are not sufficient to locate exactly where in the sky the signals are coming from. For example- first detected gravitational waves by LIGO could only pinpoint the location of the black hole merger source to a broad area of the southern hemisphere sky. LIGO observatory could not detect the precise location from where these waves came from. Therefore a third detector VIRGO-in Italy was turned on which along with LIGO confirmed more set of GW and with more preciseness this time. Thus, with the coming up of LIGO-India more accuracy will be attained in the location of the GW.