India's 4-Kilometre Gravitational-Wave Detector, Proposed in 2011, Broke Ground at Aundha in Hingoli on 23 April 2026

LIGO-India, India’s gravitational-wave detector, broke ground on 23 April 2026 at Aundha in Maharashtra’s Hingoli district, according to a LIGO Laboratory release from Caltech. It will be a near copy of the two LIGO detectors in the United States, with two arms each 4 kilometres long, and Caltech gives 2030 as the target date for its first observations.

The Union Cabinet announced in-principle approval on 17 February 2016 and cleared construction on 6 April 2023. The Press Information Bureau (PIB) gives the approved cost as ₹2,600 crore.

Who pays for what

LIGO-India is a project of the Department of Atomic Energy (DAE) and the Department of Science and Technology (DST), with DAE as lead agency. The US National Science Foundation is the partner under a memorandum of understanding that the PIB dates to 30 March 2016.

The LIGO Laboratory, which Caltech and MIT run, supplies the hardware for a complete interferometer (a measuring instrument built around laser light, explained below), its design data and training. India supplies the site, the vacuum system and the buildings, and pays for all labour and materials to install and run the instrument, the LIGO-India website says. The website adds that the components were already made during the Advanced LIGO project in the US. Nature India reported in 2025 that the US will start sending hardware in the coming years, in step with construction.

Four Indian institutions share the work, according to the project website. The Directorate of Construction, Services and Estate Management (DCSEM) in Mumbai handles land and civil works. The Institute for Plasma Research (IPR) in Gandhinagar takes the vacuum system. The Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune chose the site and will run data analysis. The Raja Ramanna Centre for Advanced Technology (RRCAT) in Indore handles optics, installation and commissioning. The Caltech release says more than 60 Indian institutions are expected to contribute over the project’s life. Once built, the PIB says, it will run as a national facility.

From a November 2011 proposal to a seven-year wait

The proposal went to DST and DAE on 15 November 2011, according to the LIGO document archive. Its authors were Bala Iyer, Tarun Souradeep, C. S. Unnikrishnan, Sanjeev Dhurandhar, Sendhil Raja and Anand Sengupta. In a 2012 talk, Unnikrishnan of the Tata Institute of Fundamental Research described LIGO-India as following an earlier plan to put a third detector in Australia. In August 2012 the US National Science Board authorised the change in scope that allowed an advanced detector to be relocated to India.

The Cabinet’s in-principle approval was announced on 17 February 2016. The PIB release noted that it came days after the detection of gravitational waves was made public, and it gave no cost. The government later told the Lok Sabha, on 30 March 2022, that the estimate at that stage was ₹1,260 crore and that DAE had sanctioned ₹75 crore for pre-investment work.

The Cabinet cleared construction on Thursday, 6 April 2023, Deccan Herald reported the next morning, at an estimated ₹2,600 crore. Nature India put the gap between the two approvals at seven years. Caltech’s April 2023 release converted the cost to about $320 million.

Aundha, 174 acres and a 48-month contract

The site covers 174 acres and was chosen for low seismic noise, the Caltech release says. Sanjit Mitra of IUCAA told Deccan Herald that the area also has little rain and wind, both of which can disturb the readings. Hingoli was named the primary site in a PIB reply of 18 July 2018, when land acquisition was described as being at an advanced stage. Nature India lists a year-long seismic study at five stations, geotechnical surveys and an on-site estate and maintenance building as pre-construction work. Foundation stones were placed at the site in 2023, Caltech says.

On 24 February 2026 Larsen & Toubro announced that two of its business verticals had won a DAE order for the observatory. The company’s scope covers vibration-sensitive civil works and an 8-kilometre ultra-high-vacuum beam tube, and the deadline is 48 months. L&T did not state the order value. It classed the order as “significant”, which on its own scale means ₹1,000 crore to ₹2,500 crore.

Deccan Herald reported in April 2025, citing the tender document, a construction budget of ₹1,600 crore. It said the other ₹1,000 crore of the ₹2,600 crore would go on sensors and detectors. Sameer Jadhav, the engineer in charge from DCSEM, broke ground on 23 April 2026 at a ceremony that DAE Secretary Ajit Kumar Mohanty also attended. That is the latest official milestone tuput could find.

How a pair of 4-kilometre tubes measures a gravitational wave

Each LIGO detector is an L. Two steel vacuum tubes, each 4 km long and 1.2 metres wide, meet at a right angle, Caltech’s LIGO site explains. A laser beam is split in two, each half travels down one arm, bounces off a mirror at the far end and returns to be recombined. By studying how the two halves interfere, scientists can tell whether a gravitational wave has passed.

The distances involved are about one-thousandth the width of a proton, Caltech says. The LIGO-India project pages give the laser’s wavelength as 1064 nanometres and say a 2-watt seed beam is amplified to 200 watts. The mirrors are 34 centimetres across, weigh 40 kg and hang on pendulum suspensions that isolate them from vibration.

LIGO-India will use the Advanced LIGO design of the Hanford and Livingston detectors. Rana Adhikari of Caltech said in the April 2026 release that the team expects it to be more sensitive and more modern than the original instruments, and that what goes in will be “fresh off the block”.

What a third detector adds to the sky map

Two detectors such as Hanford and Livingston can confirm that a signal is real, Caltech says, but cannot pin down where it came from or reveal the wave’s polarisation (the direction in which it oscillates). A third detector allows triangulation, and a network of Hanford, Livingston and Virgo still gives a sharp position for only about half the sky, the LIGO-India page on Caltech’s site says. It adds that four comparable detectors are needed to locate a source anywhere.

Caltech’s April 2023 release gave an example. Two LIGO detectors place a neutron-star merger within 100 to 1,000 square degrees of sky. With India added, the area falls to about 10 square degrees. A full moon covers about 0.2. Adhikari said localisation would improve by an order of magnitude. LIGO-India would be the fifth detector in a network with Virgo in Italy and KAGRA in Japan, and its position on the far side of the Earth fills gaps in the current coverage.

Telescopes have to search the patch of sky a detector gives them, so a smaller patch means a faster search. Mansi Kasliwal of Caltech said in the 2026 release that the baseline would let astronomers triangulate neutron-star mergers to a much smaller area and see their light. What the detectors have found so far is covered in our piece on hearing black holes collide.

The Indian names on the 2015 discovery paper

The two US detectors recorded the signal named GW150914 at 09:50:45 UTC on 14 September 2015. The discovery paper appeared in Physical Review Letters on 11 February 2016. The detection earned three of LIGO’s founders the 2017 Nobel Prize in Physics, one of the prizes in our guide to the science Nobels of 2016 to 2026.

Counting the affiliations printed on the paper, tuput found 37 of its roughly 1,000 authors listing an Indian institution. Some also list a second affiliation abroad, so the figure depends on how it is counted. The nine institutions are IUCAA in Pune, the International Centre for Theoretical Sciences of TIFR in Bangalore, the Chennai Mathematical Institute, RRCAT, IIT Gandhinagar, IPR, TIFR in Mumbai, IISER Thiruvananthapuram and IISER Kolkata.

IUCAA’s release at the time credited its scientists with two contributions. The first was the 1991 idea of matching thousands of predicted wave patterns against detector data, from Dhurandhar and B. Sathyaprakash, then an IUCAA postdoctoral fellow. The second was the theory behind a test of whether signals in separate detectors share an origin, laid by Sukanta Bose, Dhurandhar and Archana Pai. Souradeep, then spokesperson of the Indian consortium IndIGO, said a network of three detectors would localise a source much more accurately. IUCAA astronomers also joined the search for an afterglow after the signal.

How the completion date and the cost have moved

Unnikrishnan’s 2012 talk expected India to be operating an advanced detector by 2022. A PIB reply of 18 July 2018 said LIGO-India was scheduled to be operational in 2024. Caltech’s April 2026 release gives 2030 for first observations, and Nature India also reported 2030 for operation. L&T’s 48 months, counted from its February 2026 award, would end in early 2030. That deadline covers civil works, the vacuum system and utilities, and L&T’s release does not list installation and testing of the interferometer itself.

The cost figure has also changed in the public record. The in-principle estimate cited in 2022 was ₹1,260 crore, and the 2023 approval was ₹2,600 crore. The PIB releases tuput found do not explain the difference. The ₹1,600 crore and ₹1,000 crore split between construction and instruments is Deccan Herald’s reading of the tender document.