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Oct 31, 2017 - The equivalent of 3 solar masses has been carried away as gravitational waves. The milestone of detecting gravitational waves was achieved using a pair of giant laser detectors in the U.S located in Louisiana and Washington State. LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY ...
GEOGRAPHY 1. PRELIMS CURRENT AFFAIRS 2018

GRAVITATIONAL WAVE

31.10.17

Gravitational waves are 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. Einstein's mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that 'waves' of distorted space would radiate from the source. Furthermore, these ripples would travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself. The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of stellar cores (supernovae), coalescing neutron stars or white dwarf stars, the slightly wobbly rotation of neutron stars that are not perfect spheres, and the remnants of gravitational radiation created by the birth of the Universe itself. The researchers have detected the first gravitational waves coming from two black holes that orbited one another, spiraled inward and smashed together. The waves were the product of a collision between two black holes around 30 times as massive as the sun, located 1.3 billion light years from earth. A new black hole with a mass of 62 suns is formed. It is larger than each of the ones that merged. The black holes that merged were 36 and 29 solar masses respectively - but less than the sum of their masses. The equivalent of 3 solar masses has been carried away as gravitational waves. The milestone of detecting gravitational waves was achieved using a pair of giant laser detectors in the U.S located in Louisiana and Washington State.

LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY (LIGO) The Laser Interferometer Gravitational-Wave Observatory (LIGO) is designed to open the field of gravitational-wave astrophysics through the direct detection of gravitational waves predicted by Einstein’s General Theory of Relativity. LIGO’s multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves from cataclysmic cosmic sources such as the mergers of pairs of neutron stars or black holes, or by supernovae. LIGO consists of two widely separated interferometers within the United States— one in Hanford, Washington and the other in Livingston, Louisiana—operated in unison to detect gravitational waves. LIGO, is so sensitive that it can detect a gravitational wave that stretches space-time by as little as one ten-thousandth of the width of a proton. It operates on the principle that a gravitational wave stretches space in one direction while compressing space in the direction that is at right angles to the first. It has two sites 3,000 km apart to eliminate false positives (only a real gravitational wave will show up at both sites). At each site, an intense laser beam is split in two. The halves are sent to and fro along tunnels 4 km in length but built at right angles to one another. If no gravitational waves disturb the laser beams, they will arrive at the detector and interfere and cancel each other. But if a gravitational wave were to pass, the laser beams would be stretched and compressed and reach the detector out of step, causing a spike of light. 

The successful capture of gravitational waves by LIGO is a testimony to humankind’s scientific and engineering expertise to build extraordinarily sensitive instrumentation capable of detecting variations of the order of a thousandth of the diameter of a proton. Detectors in many more directions are needed so that the exact route of the gravitational wave can be traced. Therefore a facility is being planned in India in a direction opposite to the two American observatories in Louisiana and Washington.

LIGO – INDIA Localisation of a source is done by the technique of triangulation, with a minimum of three stations, and the accuracy of this technique increases with longer baselines between any two of the instruments. The baseline between Louisiana and Washington corresponds to just a 7-10 millisecond (ms) time delay for a signal at the speed of light. Imagine if there had been a LIGO-India set-up and working, the time delay between LIGO and India would have been much greater, about 36-39 ms, which would have narrowed down the localisation to a small 5-10 square degree patch in the sky, which is nearly a factor of hundred better. The maximum separation possible on the globe is 42 ms, which is between the two poles of the Earth, and the baseline delay with India would be nearly that value. Therein lies the importance of a LIGO-like instrument in this part of the world. LIGO-India is being envisaged as a collaborative project between a consortium of Indian research institutions, the LIGO Lab in the US and its other international partners.The Centre has offered a funding of Rs 1,200 crore for the project. While the LIGO lab is set to provide the complete design and the key detector components, Indian scientists will be responsible for the infrastructure to install the detector at a suitable site in India.



The entire infrastructure will be India’s responsibility. The three lead institutions in the execution of the project will be the IUCAA, the Institute of Plasma Research in (IPR) in Ahmedabad, and the Raja Ramanna Centre for Advanced Technology (RRCAT) in Indore. Though Indian scientists were part of the LIGO project, their involvement was limited to theoretical aspects and data analysis. The LIGO-India project will change this altogether as the construction, commissioning and running of the observatory will be India’s responsibility. It will offer unprecedented opportunities for Indian industry and scientists from diverse fields to be actively involved in a scientific project of a scale never before seen in the country. For instance, though many of the critical components such as mirrors and lasers will be shipped from the U.S., an ultra-high capacity vacuum system that can handle one million litres of vacuum (as in the case of CERN), and secondary optics, have to be manufactured in India. An active programme to develop optics for the laser system that could be used in future upgrades to the detectors is already under way at the Indore-based Raja Ramanna Centre for Advanced Technology. Currently only a few students from Indian institutions are able to participate in the LIGO project, but this will change completely when the observatory becomes operational in India, providing easier access for a larger number of students. Besides playing a pivotal role in gravitational wave astronomy, the Indian observatory could thus be a catalyst in changing the landscape of Indian scientific efforts. Together with other mega projects such as the India-based Neutrino Observatory project, experimental science will at last get a muchneeded boost in the country. Other than the benefit of having a third detector, which will likely improve the chances of spotting gravitational waves, an India detector would improve the chances of novel, exciting discoveries being made out of India and being made by Indians.

LOCATION OF GRAVITATIONAL WAVES OBSERVATORIES

IMPORTANCE OF GRAVITATIONAL WAVES The detection of ripples in space-time, known as gravitational waves, here on Earth marks a watershed moment for astronomy and for science as a whole. The finding completed the scientific arc of prediction, discovery and confirmation: first they calculated what they should be able to detect, then decided what the evidence should look like, and then devised the experiment that clinched the matter.



The detection at once improves our understanding of the workings of the universe and, more important, throws open a big opportunity to study it from completely new angles. It opens the way to get information about the evolution of galaxies and black holes. There is also a symmetry to the timing of the discovery: it comes a century after Albert Einstein’s general theory of relativity held that acceleration of massive bodies should produce gravitational waves, which travel through the universe at the speed of light. We have observed the universe through light so far. But we can only see part of what happens in the universe. Light, ultraviolet, X-rays, radio waves and other forms of electromagnetic radiation are easily absorbed by dust and gas, leaving much of the universe hidden. Gravitational waves carry completely different information about phenomena in the universe. So we have opened a new way of listening to a broadcasting channel which will allow us to discover phenomena we have never seen before.

PREVIOUS YEAR QUESTIONS (PRELIMS) 1. What is the purpose of ‘evolved Laser Interferometer Space Antenna (eLISA)’ project? (2017) (a) To detect neutrinos (b) To detect gravitational waves (c) To detect the effectiveness of missile defence system (d) To study the effect of solar flares on our communication systems