Gravitational waves

A vision vindicated

Print edition : March 18, 2016

Figure 1: The immense promise of LIGO-India in enabling localisation of gravitational-wave events in the sky and launching gravitational-wave astronomy. The grey banana-shaped patch spanning 2,500 moons is the current uncertainty of the localisation of the first discovery event. The small dark ellipse that is 100 times smaller shows the forecast uncertainty for a similar gravitational-wave signal when LIGO-India is operational.

Figure 2: Engineering concept design of LIGO-India at one of the shortlisted sites in India. Terrain data obtained from Space Applications Centre, ISRO (Courtesy: Tata Consulting Engineers Ltd., India).

The impact of LIGO-India will be multifaceted and would push the frontiers along each direction (LIGO-India proposal document, November 2011).

The LIGO-India project, which has been approved by the Union Cabinet, was a vision of the IndIGO Consortium, a multi-institutional multidisciplinary collaboration that now includes nine of the country’s leading scientific research institutions.

WITH the momentous announcement of the first detection of a gravitational-wave (GW) event by the Laser Interferometer Gravitational-wave Observatory (LIGO) in the United States on February 11, swiftly followed by the Indian Cabinet’s in-principle approval of the LIGO-India project, the Indian Initiative in Gravitational-wave Observations (IndIGO) Consortium can proudly feel that its “decadal” vision and plans have been vindicated spectacularly. This is just the first step, and far tougher challenges lie ahead for this “social experiment” of multi-institutional scientific collaboration in India through an informal consortium.

A few years into the present millennium, during the phase of operation with the Initial LIGO detector in the U.S. and its close cousin, VIRGO, in Italy, concrete plans for an advanced detector configuration achievable by 2015 were being drawn up. They indicated that the next generation of GW detectors would allow a 10-fold improvement in sensitivity. That meant a 1,000-fold increase in the expected rate of cosmic events that would produce detectable GW signals on earth, to more than one event a year even in fairly pessimistic astrophysical scenarios. It was eminently clear that the detection of GW signals from astrophysical phenomena, in particular the merger of compact neutron star binaries and black hole binaries, was almost guaranteed with the experimental runs of the advanced LIGO detectors.

A few researchers in India recognised the great opportunity it provided to the Indian scientific community if it could gear up, plan, and prepare a decade in advance for carrying out research in this emerging field. In a radical departure from the norm, Indian scientists would then be well entrenched in an emergent frontier field well before it had blossomed and gone far ahead out of reach. (An unfortunate example of the usual norm is the field of cosmic microwave background (CMB) fluctuations that has revolutionised cosmology from 1990 to date. Here, despite the obvious promise of the first detection by NASA’s Cosmic Background Explorer in 1992, neither an Indian research community of substance in the field grew nor plans for experiments were launched.)

Though the direct detection of GW was the first mandate of the kilometre-scale laser interferometric GW detectors, more than the discovery itself, the excitement following the first detection relates to the opening up of a new observational window into the dark universe that translates to a new handle to understand astrophysics and cosmology, maturing into an experimental probe for basic physics.

All this is possible since GW signals propagate un-attenuated. GW observations can provide details not accessible to astronomy with different frequencies of the electromagnetic spectrum such as visible, IR (infrared) and UV (ultraviolet), X-rays and gamma rays, and are capable of uncovering new aspects of physics. All relativistic theories of gravitation, such as Einstein’s general theory of relativity, predict GW, but important properties of GW, such as its speed of propagation or number of polarisation states, differ in alternative theories of gravitation. Finally, GW from coalescing compact binaries of neutron stars and black holes probe Einstein’s gravitation in regions of strong gravitational field involving matter moving at speeds comparable to the speed of light, well beyond the regimes of tests possible before.

In 2010, the Gravitational Wave International Committee (GWIC) prepared a global road map for gravitational wave detection and astrophysics with a 30-year horizon. An important item in the executive summary was the following: “A true global array of gravitational-wave antennae separated by intercontinental distances is needed to pinpoint the sources on the sky and to extract all the information about each source’s behaviour encoded in the gravitational wave signal… .First priority for ground-based gravitational-wave detector development is to expand the network, adding further detectors with appropriately chosen intercontinental baselines and orientations to maximise the ability to extract source information.”

It is well recognised in the scientific community that, beyond the first detection, GW science and astronomy has a vast scope over the next few decades for furthering the frontier with the addition of GW detectors worldwide. As early as 2007, at the International Conference in Gravitation and Cosmology (ICGC) meeting at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, Rana Adhikari of Caltech, one of the nodal institutes operating the LIGO detectors, suggested to IUCAA scientists Tarun Souradeep (an author of this article), Anand Sengupta and Sanjit Mitra that it was time to think about a GW detector in India, which was also christened IndIGO.

One option was to explore the possibility of putting together a high frequency detector in India using critical components that would be available when the Initial LIGO detector was decommissioned. In parallel, in 2008, a project called “Indo-Australian collaboration on GW Astronomy” was funded by the Australia-India Strategic Research Fund (AISRF), with Bala Iyer (an author of this article) and David Blair, a gravitation physicist at the University of Western Australia, as principal investigators.

Formation of IndIGO

In August 2009, at a meeting in the IUCAA, the IndIGO Consortium, which collectively had expertise in theoretical and experimental gravity, cosmology and optical metrology, was formed. The consortium sought to promote GW research in the country with a dream of realising an advanced detector in India in the same time frame as the global advanced generation of detectors. The consortium planned for the participation of the Australian International Gravitational Observatory (AIGO), the proposed Australian detector, with a 20 per cent contribution to the detector cost.

LIGO consists of two sites (one in Hanford, Washington, and the other in Livingston, Louisiana). The original advanced LIGO project envisaged three detectors, with two advanced detectors in the same beam tube at Hanford. Realising its strategic importance for GW astronomy, LIGO laboratories looked into the possibility of relocating the second Hanford detector to Australia as LIGO-Australia. A fourth site, not in the plane formed by the two U.S. LIGO sites and VIRGO, and located far from them, would greatly improve the ability to localise GW sources in the sky. This improved source location is critical for GW observations to become a part of the new wave of multi-messenger astronomy, which means doing astronomy using multiple windows of observation in parallel. Additional detectors would also lead to increased event rates, improved duty cycle, improved detection confidence, improved sky coverage, and improved determination of the polarisation of the GWs. Since GWs provide complementary information by other means, by combining observations of a single event using different probes, it is possible to gain a more complete understanding of the source’s properties.

IndIGO interacted with GWIC to explore ways to extend the International Advanced GW Network by participating in LIGO-Australia. When it seemed funding for LIGO-Australia may not be forthcoming from the Australian government, preliminary discussions for relocating the second advanced Hanford interferometer to India (as LIGO-India) were initiated in June 2011 through IndIGO by Abhay Ashtekar, the well-known gravitation theorist from Pennsylvania State University, U.S., at the highest levels of Indian science decision-making. As the Chair of IndIGO’s International Advisory Committee, Ashtekar played a crucial role in taking forward the Indo-U.S. collaboration relating to LIGO-India. Strong encouragement to IndIGO for pursuing a LIGO detector on Indian soil came from science luminaries such as Dr Anil Kakodkar (former Chairman, Atomic Enery Commission and then Chairman, IUCAA Governing Board), Dr Srikumar Banerjee (then Chairman, AEC), Dr K. Kasturirangan (Former Chairman, Indian Space Research Organisation, and then member of the Planning Commission), and famous scientists and institution-builders Jayant Narlikar, Govind Swarup and Predhiman Kaw. It was a great learning experience for us to work with Stanley Whitcomb, Fred Raab and Dave Reitze from LIGO U.S. towards realising LIGO-India. Working towards this shared dream built a precious relationship with them. Their untiring enthusiasm and vast experience were an inspiration to all of us.

The LIGO-India proposal is for the construction and operation of an Advanced LIGO Detector (with a displacement sensitivity of 4x10 -20 m) in collaboration with LIGO Laboratories, U.S. The objective is to set up the Indian node of the three-node global Advanced LIGO detector network by 2022 and operate it for 10 years. The inclusion of LIGO-India greatly improves the angular resolution in the location of the GW source by the LIGO global network. For the specific event detected by the two advanced LIGO detectors in February, with a hypothetical LIGO-India in operation, there would have been a 100-fold improvement in the angular resolution. This indeed is a startling attestation to the promise of LIGO-India.

The formal offer for the LIGO-India joint collaboration was made by LIGO Laboratories in October 2011. The LIGO-India proposal was submitted to the Department of Atomic Energy (DAE) and the Department of Science and Technology (DST) in November 2011 and it was presented at the meeting of the Planning Commission on Mega Projects in Delhi. The lead institutions for the project were identified in December 2011 as the Institute for Plasma Research (IPR), Gandhinagar, the IUCAA, and the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, with the project work subdivided into broad, activity-wise categories.

The entire hardware component of the advanced LIGO detector, along with design and software, is to be provided by LIGO-U.S. and its United Kingdom, German and Australian partners. The entire infrastructure, including the two four-kilometre ultra-high vacuum (UHV) beam tubes, with associated chambers, corner and end stations (of the L-shaped interferometer), related labs and clean rooms, as well as the team to build and operate the observatory will be the Indian responsibility. LIGO Laboratories is committed to sharing and providing detailed designs and documentation of all aspects of the LIGO detector. It would also assist during installation, commissioning and noise-limited operation at the LIGO-India site.

In August 2012, the U.S. National Science Board approved the proposed Advanced LIGO Project’s change in scope, enabling plans for the relocation of an advanced detector to India. In December 2012, LIGO-India was included and figured in the list of Mega Projects in the report of the National Development Council as part of its approval of the Twelfth Five Year Plan.

LIGO-India teams at the IUCAA, the IPR and the RRCAT were working steadily even in the pre-approval period. The site selection committee at the IUCAA has looked at over 22 sites and shortlisted a few of them, based on site-selection criteria like low “seismicity” (ground noise), low human-generated noise, socio-environmental considerations of land acquisition, air connectivity, road connectivity and data connectivity.

Extensive preparation

The IUCAA has also started the science team building activity and is steadily building up a state-of-the-art computing and data infrastructure and associated manpower in anticipation of LIGO-India. The team at the IPR has prepared system requirement documents, conceptual drawings and engineering drawings for the sophisticated civil infrastructure and UHV systems in consultation with LIGO Laboratories. The team at the RRCAT has been finalising plans for setting up an off-site laboratory to receive the laser systems for LIGO-India. Its members are working on the pre-stabilised laser in collaboration with colleagues in Germany who produced the laser system and are also experimenting with the production of fused silica suspensions for the optics used in Advanced LIGO. To the extent feasible in the pre-approval phase, visits by LIGO-India team members to the LIGO, GEO600 (in Hannover, Germany), KAGRA (Kamioka Gravitational Wave Detector, Tokyo) and VIRGO detectors, which form part of the global GW detector network, have taken place.

With the approval from the Union Cabinet, the combined LIGO-India team is in a high state of readiness to start on well-planned steps. Pre-approval preparation has also involved many schools and workshops at different levels and participation in the LIGO SURF (Summer Undergraduate Research Fellowship) programme. The IUCAA and the International Centre for Theoretical Sciences-Tata Institute of Fundamental Research (ICTS-TIFR) have contributed significantly to these efforts and IndIGO received support and encouragement from their respective (former) directors, Ajit Kembhavi and Spenta Wadia, as well as their current directors, Somak Raychaudhury and Rajesh Gopakumar.

IndIGO (website: http://www.gw-indigo.org/) is now a multi-institutional, multidisciplinary consortium consisting of three lead institutions and nine nodal institutions. Starting with 14 members in 2010, it has 120 members today. While it had three experimenters then, it has 56 experimenters today. The Indian membership in the LIGO Science Collaboration, from a single group at the IUCAA during 2000-2010, has now grown to a pan-Indian group with 61 members, including 21 experimenters from nine Indian institutions, namely, the IPR, the IUCAA, the RRCAT, the TIFR, the ICTS-TIFR; the Chennai Mathematical Institute (CMI), Chennai; IIT Gandhinagar; the Indian Institute of Science Education and Research (IISER), Kolkata; and IISER-Thiruvananthapuram.

There are three unique aspects of the IndIGO Consortium that have possibly contributed to its success thus far:

1. The consortium set goals that projected well ahead into the future, allowing time for a healthy next generation of young researchers to be established. It also allowed time to consolidate expertise scattered across different laboratories in India under a common umbrella. It has also gained international recognition as a channel for Indian researchers abroad to explore possibilities of returning and contributing to the national effort.

2. The IndIGO Consortium was an informal collection of researchers devoid of any institutional affiliation. This allowed these researchers to take bold uninhibited steps driven solely by scientific and technological considerations rather than by existing funding and institutional structures. (The IndIGO Consortium enjoyed logistic support from IUCAA to carry out many of its activities and that was formalised recently in an MoU.) Despite being an informal body, the consortium was formally recognised in the global GW community with a membership in the GWIC. The consortium benefited immensely from the cooperative nature of GW endeavours.

3.The open and non-institutional nature of the consortium encouraged an influx of experts from all forms of institutional settings, national and international, such as large research laboratories, IISERs, IITs, National Institutes of Technology (NITs), and from other related fields of experimentation and theory. On the other hand, the globally cooperative and collaborative nature of GW science has instilled among the members the spirit of working effectively in a large scientific collaboration.

Over the last decade, the Indian GW community, mainly consisting of researchers trained at the research groups in the IUCAA and the RRI, have spread to take up faculty positions at a number of educational and research institutions in India. As members of the LIGO Science Collaboration, they have made major contributions to the development of novel techniques to identify the weak GW signals, enabling GW astrophysics. Other Indian researchers in IndIGO have expertise in precision metrology, laser and optics development, ultra-high vacuum techniques and control systems. A prototype detector is being built for training and research at TIFR, Mumbai. Major computing and data crunching facilities dedicated to GW science have come up in IUCAA, Pune, and will also come up at ICTS-TIFR, Bengaluru.

The approval of LIGO-India paves the road to the possibility of observing our universe through GWs. The IndIGO Consortium has also seen increasing participation from the Indian astronomy community in anticipation of this new emerging frontier of “Electromagnetic follow up” of GW events. As the Global GW Network expands to include LIGO-India, successful operation of advanced detectors will transform the field from GW detection to GW astronomy.

Wide technological impact

LIGO-India has the potential to impact precision experiments and cutting-edge technology in the country. The project has interfaces with quantum metrology, laser physics and technology, vacuum technologies, optical engineering, sensor technologies, control systems, grid and cloud computing, to list a few. As Beverly Berger of the U.S. National Science Foundation said: “Every single technology they are touching they are pushing and there is a lot of technologies they are touching.”

LIGO-India is a dream nurtured and sustained by wonderful colleagues in India and abroad over the last five years. They are too numerous to list—from heads and their colleagues in the funding agencies to directors and their colleagues in the lead institutes, from distinguished science leaders the world over to young faculty trying to make a mark in the field. IndIGO scientists look forward to working with you all to decode new mysteries revealed in the GW sky.

Tarun Souradeep is a Senior Professor at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, and spokesperson for IndIGO and Co-ordinator for LIGO-India at the IUCAA.

Bala Iyer is a Visiting Professor at the International Centre for Theoretical Sciences (ICTS) of the Tata Institute of Fundamental Research, Bengaluru, and Chairperson, IndIGO.

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