About 1,000 scientists are involved in Ligo USA, drawn from the faculty of around 90 institutions. The Italian facility, called the Virgo Collaboration, is hosted near Pisa and involves 250 scientists from 19 institutes. The Japanese facility, Kagra (Kamioka Gravitational Wave Detector) is run by a group coordinated by the Institute for Cosmic Ray Research of Tokyo University.
The IndIGO Consortium, or the Indian Initiative for Gravitational Wave Observation, also inducts scientists from many premier institutions. IndIGO is looking at two potential sites. One is in Maharashtra’s Hingoli district, the other near Udaipur. If all goes well, the facility will be operational in eight years. The US Ligo will transfer equipment worth about $140 million to India. But a lot of equipment will be manufactured in India. All the civil engineering will be done by IndIGO, which has engaged Tata Consulting Engineers to survey the sites.
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Ligo facilities detect minute gravitational perturbations from billions of light years away. They are shielded carefully to avoid false detections of passing trucks, for instance. Each Ligo has tunnels of over 8 km in length. Apart from sheer size, there are other constraints. The facility must not be near the sea. It must also be in a low seismic zone, away from railway lines and busy roads.
The Ligo labs have two tunnels joined like an “L”, with each arm of the “L” exactly 4 km long. Each tunnel has a vacuum tube running through it. A laser beam is run through the vacuum tubes. The beam splits at the intersection and each arm has mirrors to bounce that beam back and forth.
A photo detector device is placed at such an angle in the intersection that it will receive no light if the two arms stay exactly the same length. A gravity wave changes arm-dimensions and light hits the photo detector. Thus, gravitational waves are converted into optical signals, which may be recorded and analysed.
Much thought is involved in suspending mirrors, creating vacuum etc, to reduce interference. But in practice, there is always some continuous “noise” and signals must be “massaged” to eliminate lightning strikes, earthquakes, passing trucks and trains etc.
The US Advanced Ligo has been fully operational only since September 2015. It detected its first black hole collapse and merger in September itself and another such event in December. Both cases involved two black holes merging into one. The data analysis took about six months. Indian scientists were involved in key roles in data analysis where two key techniques were developed and refined by Indians.
Any event that causes gravitational waves will leave a specific shape embedded within the photo detector’s light signals. (Think of this like a musical note embedded within random background noise — in fact, scientists call the black hole merger signal a “chirp”).
Sanjeev Dhurandhar of Inter-University Centre for Astronomy and Astrophysics developed a “matched filtering” method to isolate such shapes. Bala Iyer led an Indo-French team that worked through Einstein’s equations to gauge what the shape would be for events such as black hole mergers.
In the second event, more data was generated by the Indian satellite, AstroSat, which used its Cadmium Zinc Telluride Imager to take X-ray photographs. The second event was much smaller than the first. A less powerful wave was generated and so, detection was harder. Intriguingly, scientists are speculating about the possibility that black hole mergers of holes of a certain dimension may have led to the creation of dark matter.
More physical facilities outside the US will reduce errors in detection and increase the volume of space that can be surveyed. As detectors reach farther out, they also automatically reach farther back in time. Eventually that will give us a clearer picture of what happened at the Big Bang or just after.