The first joint catch by LIGO and Virgo: another black hole merger detected

Three detectors together delivered a significantly better localization of the source and access to polarizations of gravitational waves.

The LIGO observatories in the USA observed the gravitational-wave signals from yet another merging black hole pair. This time, LIGO was joined by the Virgo observatory from Europe, which significantly contributed to the improved localization of this astronomical source in the sky, and enabled new tests of Einstein's theory based on the polarization of gravitational waves.

This event, detected on 14 August 2017, is the fourth detection of a merging binary black hole system. Three such events were detected by the twin LIGO detectors in the past (first two events in 2015 and the third one in January 2017). It is the first time that such a detection is being confirmed by a third detector. The Virgo detector started collecting data on 1 August 2017, and was soon bestowed with a detection, jointly with LIGO.

The signal was produced by the merger of two massive black holes, weighing 31 and 25 times the mass of the Sun at a distance of 1.7 billion light years away from us. An energy equivalent to the mass of three Suns was radiated as gravitational waves in this energetic astronomical event. These detections of gravitational waves from merging black hole pairs allow us to map out the distribution of black holes in the universe and to do precision tests of Einstein’s theory of General Relativity. Results from this detection are presented in a new paper accepted for publication in the journal Physical Review Letters.

The LIGO-Virgo collaboration includes more than a thousand scientists from many different countries, setting a great example in international scientific cooperation. The recent publication has 40 authors from 13 Indian institutions. Over the last three decades, Indian scientists have done foundational work in various aspects of gravitational-wave science, including theoretical calculation of expected signals from astronomical sources, developing sophisticated data analysis techniques for searching weak gravitational-wave signals in noisy data and devising techniques to combine data from multiple detectors. The current Indian team in the LIGO-Virgo collaboration has made direct contributions to the extraction of the properties of the astronomical source from the data and to the first tests of Einstein’s theory using these observations. The Indian contribution to this emerging frontier will grow significantly in the future, with the materialisation of the LIGO-India observatory, which is being built on Indian soil. This is expected to bring manyfold improvements to the source localisation accuracy.

LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at http://ligo.org/partners.php. The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in The Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and EGO, the laboratory hosting the Virgo detector near Pisa in Italy.

Indian Institutions involved in the current work, and corresponding contact persons:

IndIGO-LSC Principal Investigator

Bala Iyer (ICTS) E-mail: , Tel. 9739373144

LIGO-India spokesperson:

Tarun Souradeep (IUCAA) E-mail: , Tel. 9422644463

IUCAA - Inter University Centre for Astronomy and Astrophysics, Pune

Sanjit Mitra E-mail: , Tel. 8275067686

RRCAT - Raja Ramanna Centre for Advanced Technologies, Indore

IPR - Institute for Plasma Research, Gandhinagar

CMI - Chennai Mathematical Institute

K G Arun E-mail: , Tel. 9500066350

ICTS - International Centre for Theoretical Sciences (TIFR), Bengaluru

P. Ajith E-mail: , Tel. 9164594474

TIFR - Tata Institute of Fundamental Research, Mumbai

A. Gopakumar E-mail: , Tel. 9869039269

C. S. Unnikrishnan E-mail: , Tel. 9869564290

IISER-Kolkata - Indian Institute of Science Education and Research Kolkata

Rajesh Kumble Nayak. E-mail: , Tel. 9903507977

IISER-TVM - Indian Institute of Science Education and Research Thiruvananthapuram

IIT Bombay - Indian Institute of Technology Bombay

Archana Pai E-mail: , Tel. 9037573123

Varun Bhalerao E-mail: , Tel. 9850005899

IIT Chennai - Indian Institute of Technology Chennai

Chandra Kant Mishra E-mail: , Tel. 8748816343

IIT Gandhinagar - Indian Institute of Technology Gandhinagar

Anand Sengupta E-mail: , Tel. 8758146696

IIT Hyderabad - Indian Institute of Technology Hyderabad

UIAR - University and Institute of Advanced Research, Gandhinagar

Gurudatt Gaur E-mail: , Tel. 9537672348