Gravitational Waves Detected 100 Years After Einstein’s Prediction Ligo Opens New Window On The Universe With Observation Of Gravitational Waves From Colliding Black Holes[iiser Trivandrum Scientists Make Contribution To The Discovery]

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For the first time, scientists have observed ripples in the fabric of space-time called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. This collision of two black holes had been predicted but never observed.

The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (9:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.

The black hole binary now termed as GW150914 was detected with very high confidence level of greater than 5.1 sigma level. This level translates into having very small chance coincidence of noise mimicking the event. For example it is like tossing a fair coin with 22 heads in a row. Based on the observed signals, LIGO-Virgo Science Collaboration estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About 3 times the mass of the sun was converted into gravitational waves in a fraction of a second. The detector in Livingston recorded the event 7 milliseconds before the detector in Hanford, 3000 km north-west of Livingston, which locates the source in the southern hemisphere.

A century ago, Einstein predicted gravitational waves in his Theory of General Relativity. According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final moments. During the final fraction of a second, the two black holes collide into each other at nearly one-half the speed of light and form a single more massive black hole, emitting a burst of energy. It is this signal the two LIGO detectors have observed.

In 1974, Russell Hulse and Joseph Taylor, Jr., discovered the first binary pulsar ( a pulsar and a neutron star in a orbit). Later with Weisberg , Taylor showed that the orbit of the pulsar was slowly shrinking over time because of the release of energy in the form of gravitational waves. Hulse and Taylor were awarded the Nobel Prize in Physics in 1993 for the discovery of this peculiar binary system.The Hulse-Taylor binary system will merge into a black hole 300 million years from now. In the measurement just made, LIGO directly observed the gravitational waveform from the end of the life of a black hole binary, giving a sketch in time of the final fractions of a second of this binary system as it became a single black hole.

Merger of black holes is a regime of strong gravity where Einstein's theory was never tested. Gravitational Wave group at IISER Trivandrum directly contributed in Testing General Relativity with GW150914 along with the colleagues of LIGO-Virgo Science Collaboration (which includes IndIGOLSC colleagues). With extensive computational analysis, the study found that the emitted signal is consistent with the predictions of general relativity.

LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.

LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. The LSC detector network includes the LIGO interferometers and the GEO600 detector. The GEO team includes scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI), Leibniz Universität Hannover, along with partners at the University of Glasgow, Cardiff University, the University of Birmingham, other universities in the United Kingdom, and the University of the Balearic Islands in Spain.

Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups: 6 from Centre National de la Recherche Scientifique (CNRS) in France; 8 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; 2 in The Netherlands with Nikhef; the Wigner RCP in Hungary; the POLGRAW group in Poland and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy.

The discovery was made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first generation LIGO detectors, enabling a large increase in the volume of the universe probed—and the discovery of gravitational waves during its first observation run. The US National Science Foundation leads in financial support for Advanced LIGO. Funding organizations in Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council, STFC) and Australia (Australian Research Council) also have made significant commitments to the project. Several of the key technologies that made Advanced LIGO so much more sensitive have been developed and tested by the German UK GEO collaboration. Significant computer resources have been contributed by the AEI Hannover Atlas Cluster, the LIGO Laboratory, Syracuse University, and the University of Wisconsin-Milwaukee. Several universities designed, built, and tested key components for Advanced LIGO: The Australian National University, the University of Adelaide, the University of Florida, Stanford University, Columbia University in the City of New York, and Louisiana State University.

LIGO Science at IISER TVM

The Indian participation in the LSC, under the umbrella of the Indian Initiative in Gravitational-Wave Observations (IndIGO), involves sixty-one scientists from nine institutions - CMI Chennai, ICTS-TIFR Bengaluru, IISER-Kolkata, IISER Trivandrum, IIT Gandhinagar, IPR Gandhinagar, IUCAA Pune, RRCAT Indore and TIFR Mumbai with 37 authors on the discovery paper. The gravitational wave group at School of Physics, IISER Trivandrum, headed by Archana Pai is a member of IndIGO consortium — a consortium of Indian research groups with common interest in research in gravitational wave physics and experiments. The IISER Trivandrum group is a member of LSC since March 2012 through IndIGO-LSC group. Trained as a Gravitational Wave Physicist, Archana Pai carried out PhD under supervision of Prof. Sanjeev Dhurandhar at IUCAA, Pune on gravitational wave multi-detector strategies in 2001. This work is relevant now in the context of discovery with two LIGOs and with more advanced detectors coming online in next years. Prof Sanjeev Dhurandhar who is a frequent visitor of IISER Trivandrum and who lead the gravitational wave research group at IUCAA for about 15 years quotes in the regard ’It is fantastic feeling to know that a substantial part of the work done by the gravitational wave group at IUCAA has borne fruits with the spectacular discovery of gravitational waves from colliding black holes ‘.

The IISER Trivandrum group focuses on novel gravitational wave detection algorithms, extracting astrophysical parameters with possible joint observation with electromagnetic counterparts and Testing General Theory of Relativity using the global network of interferometers such as LIGOs, French Italian Virgo detector located in Pisa, Italy, Japanese detector KAGRA. The research is centred around the astrophysical binary system with neutron stars and black holes. Over the past six years, the group has mentored post-doctoral fellows, PhD and project students through institute summer program, external grants and international programs such as Max Planck Partner Group.

The discovery paves the road to the possibility of observing our universe in gravitational waves if one can locate their source with additional detectors placed far from the LIGO detectors, in a large triangle. This would improve to locate the source more accurately which would open up new avenues in the joint observation of electromagnetic and gravitational wave window.

The research activities are supported by the Ministry of Education and Department of Science and Technology.

IndIGO-LSC Contact at IISER Trivandrum:

Archana Pai, School of Physics, IISER Trivandrum Email:archana[at]iisertvm[dot]ac[dot]in (0471-2599423)
IndIGO-LSC group members at IISER Trivandrum : K. Haris, M. Saleem, V. Gayathri and Kumar Atmjeet.