‘Gravitational waves herald a new era in astronomy’

For many centuries, all of astronomy has relied exclusively on understanding the Universe by capturing visible light through our telescopes. In the last 50 years, astronomers have learnt to study the Universe in all bands of light, from Gamma-rays and X-rays to Infrared and Radio.

“In the last few decades, we have also been using neutrinos and cosmic rays to peer deep into our Universe. However, gravitational waves, recently detected by Laser Interferometric Gravitational Observatory (LIGO), are an entirely new messenger of what is happening in space”, said Prof. Ajith Parameswaran.

He was delivering a special lecture titled “Einstein’s Messengers” at the 36th national meeting of the Astronomical Society of India at Osmania University. Gravitational waves were detected first on 14 Sept 2015 by LIGO, from the merger of two black holes. Since then, a handful of similar events have been discovered, arising from the final death throes of two black holes colliding and merging to form a new black hole. These discoveries earned the Physics Nobel Prize for 2017. Prof Ajith then went on to emphasise the importance of the latest detection of gravitational waves from a pair of merging neutron stars.

Following this detection, more than 80 telescopes around the world immediately turned their attention to this patch of the sky, and found electromagnetic radiation, or light, from this event. “Astronomers could locate the exact galaxy where this merger took place, and a new era of astronomy was born”, said Prof Ajith. The afterglow from this cataclysmic event was detected later by the Giant Metrewave Radio Telescope near Pune, and was also followed by AstroSat and the Himalayan Chandra Telescope as well. The detection of these waves by LIGO was an unprecedented feat in engineering. “They had to measure the change in the length of a 4 km long tunnel by not more than the size of proton”, he said.

Prof Ajith then talked about the excitement around the Indian gravitational observatory that is coming up soon, LIGO-India. This observatory will work in consonance with the existing LIGO instruments around the world. “Using current gravitational-wave observations, we are unable to identify their arrival directions very precisely — we can only tell that the merger event happened somewhere within a large part of the sky”, said Prof Ajith. However, LIGO-India will improve this enormously.

Indian astronomers are gearing up to meet the challenge of setting up and running LIGO-India. Collaborations have been set up across the country, involving research institutes and universities, and training workshops are regularly conducted for college students. “We cannot wait to see what LIGO-India will teach us,” said Prof Ajith.

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