“This is the first time the universe has spoken to us – through gravitational waves,” said David Reitze, executive director of the Laser Interferometer Gravitational-wave Observatory project.

On September 14, 2015 a team of scientists at Livingstone, Louisiana picked up a signal from the far reaches of space. Seven milliseconds later they saw the same signal at Hanford, Washington. After months of checking their data, the team announced on Thursday, February 11, that the two signals came from gravitational waves – a holy grail of astrophysics.The detection of gravitational waves is a direct verification of Albert Einstein’s last prediction from his theory of general relativity. It is also proof that binary black holes exist, LIGO scientists said.

Here’s a short version of how the LIGO team explained the phenomenon they recorded. The wave that LIGO detected was generated 1.3 billion years ago when two massive black holes collided and merged. Each black hole was about 150 kilometers in diameter but packed with 30 times the mass of the sun. As they spun around each other, they accelerated to half the speed of light and then crashed into each other till they finally became one giant black hole. As the two black holes merged there was a burst of gravitational waves that passes through all matter in the universe to finally reach the earth and the interferometer set up to detect it.

The scientists at LIGO also converted the gravitational wave signal they saw into sound waves that allows us to hear what a pair of colliding black holes sounds like.


A hundred years ago, Einstein proposed that the universe is in the form of four-dimensional space-time. Imagine space-time to be a flexible but taut rubber sheet and stars and planets and other celestial bodies are balls dropped onto the rubber sheet. A planet curves the fabric of space-time in the same way that a ball on a rubber sheet would. When a planet moves, it causes a ripple in space-time in the same way that a ball moving in a rubber sheet would cause ripples. These ripples are gravitational waves that expand and contract all matter in the universe as they pass through it.

The LIGO experiment involves splitting a laser beam, projecting the twin beams perpendicular to each other over 4 km, bouncing them off mirrors, merging them and then looking for a signal of a G-wave in the merged beam. The binary balck hole signal was detected before the science run of the upgraded Advanced LIGO system began last year.

The LIGO discovery opens another window to explore the universe apart from using electromagnetic waves, said Anirban Kundu, a particle physicist from the University of Calcutta. “It may also tell us something about the very, very early universe when it expanded exponentially, which we call inflation,” he said. “This will open up a new observational tool of the universe, suited for drastic phenomena. This will also affect the theoretical studies on topics like black hole.”

A lot more expected from where the September 14 signal emerged. “The paper that has just been published contains a very careful statistical analysis of what this means about how often these things may occur. That analysis says we may see more over the coming year,” said Kip Thorne of Caltech, co-founder of LIGO. “Advanced LIGO is at one-third of its ultimate design sensitivity. Over the next few years the noise level will be brought down, LIGO will be three times better and we can see three times farther into the universe.”

India will have a big role to play in future detection of gravitational waves. The envisaged LIGO-India project proposal includes shifting one Advanced LIGO detector from Hanford to India. Studies have shown that adding a detector in India or Australia could increase the sensitivity of a network of detectors to gravitational waves. LIGO-India will be a collaboration between LIGO and three Indian institutions – the Institute of Plasma Research in Gandhinagar, the Inter-University Centre for Astronomy and Astrophysics in Pune and the Raja Ramanna Centre for Advanced Technology in Indore, which together form the IndIGO consortium. LIGO scientists are also looking to partner with the Virgo project in Italy to expand the g-wave network.