विज्ञान जगत

Cosmic fireworks: First joint detection of gravitational and electromagnetic waves from colliding neutron stars : Astronomers from ARIES Nainital are also a part of this Research

The​ beginning​ of​ gravitational-wave​ multi messenger​ astronomy  

17 August 2017 saw a major breakthrough in astronomy, when gravitational waves from a pair of colliding neutron stars were detected for the first time by the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Europe-based Virgo. This happens to be the strongest gravitational-wave signal detected so far, owing to the relatively close location of about 130 million light-years from earth. The detection was also confirmed by a large number of telescopes around the world that studied various forms of radiation from the merger. This is a new milestone in the success saga of advanced
gravitational wave detectors, which have announced the discoveries of four black hole mergers to date. The first such detection in 2015 led to the awarding of the Nobel prize in physics this year.

Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas. Typical neutron stars are heavier than the sun, but have a diameter of just about 20 kilometers: objects so dense that a teaspoon of neutron star material weighs more than Mount Everest. Scientists could track these neutron stars, weighing about 1.1 to 1.6 times the mass of the sun, for about 100 seconds as they spiraled towards each other in a final deadly dance and collided. These observations contain important clues about the nature of the dense matter that constitute these stars.
 
Let there be light 
The collision created a flash of gamma rays that was detected by earth-orbiting satellites just two seconds after the gravitational waves. This is the first conclusive evidence that short gamma ray bursts, often seen by orbiting satellites, are indeed created by colliding neutron stars — something that had only been speculated for decades. The near-simultaneous arrival of gravitational waves and gamma rays from a source that is 130 million light years away confirms that gravitational waves indeed travel with the speed of light, as predicted by Einstein’s theory. These joint observations also provided scientists an independent way of measuring the expansion rate of the universe.
 
Striking gold 
In the days that followed, astronomers pinpointed the source on the sky and studied it extensively in various forms of electromagnetic radiation, including X-ray, ultraviolet, optical, infrared, and radio waves. These joint observations clearly show that at least some short gamma-ray bursts, the energetic flashes of gamma rays, are generated by the merging of neutron stars — something that was only theorized before. These studies showed signatures of newly synthesized elements, confirming that such mergers are indeed the birthplaces of half of the elements heavier than iron – including most of the gold and platinum in the universe.
 
Indian contributions 
Indian scientists have made pioneering contributions to the gravitational-wave science over the last three decades. 40 scientists from 13 Indian institutions are part of the LIGO-Virgo discovery paper. Indian scientists contributed to the fundamental algorithms crucial to search for inspiraling binaries in noisy data from multiple detectors, in computing
waveforms for these signals by solving Einstein’s equations, in separating astrophysical signals from numerous instrumental and environmental artefacts, in interpretation of joint gravitational-wave and gamma-ray observations, tests of Einstein’s theory and many other aspects of the data analysis. In addition, several Indian telescopes such as AstroSat, Giant Metrewave Radio Telescope (GMRT) and the Himalayan Chandra Telescope (HCT) participated in the search for electromagnetic flashes. The sensitive CZTI instrument on AstroSat helped narrow down the location of the gamma-ray flashes. HCT obtained optical images at locations of neutrinos detected by other telescopes at the same time as the
burst, and showed that they were unrelated to the gravitational-wave trigger. GMRT played a key role in understanding jet physics and refining models of radio emission from the remnant formed by the merging neutron stars.

The Indian team in LIGO includes scientists from CMI Chennai, ICTS-TIFR Bangalore, IISER Kolkata, IISER Trivandrum, IIT Bombay, IIT Gandhinagar, IIT Hyderabad, IIT Madras, IPR Gandhinagar, IUCAA Pune, RRCAT Indore, TIFR Mumbai and UAIR Gandhinagar. Astronomers from IISER Pune, IIT Bombay, IUCAA Pune, TIFR Mumbai, PRL Ahmedabad, IIT Hyderabad, IIA Bangalore, NCRA-TIFR Pune, ARIES Nainital and IIST Trivandrum participated in the electromagnetic follow-up of this event using a variety of telescopes. Astronomers from ARIES Nainital are also a part of this Research , which includes Dr. Kuntal Mishra & Dr. Sashi Bhushan Pandey

The planned LIGO-India detector, to be funded by Department of Atomic Energy (DAE) and the Department of Science & Technology (DST), will increase the sensitivity of the international gravitational-wave network and produce many fold improvement to the localisation of the sources. Astronomers will then be able to identify the exact location of the cosmic explosion a lot quicker, and study right from the first moments in every frequency band of the electromagnetic spectrum.