LIGO Detectors

About Gravitational Waves:

• Gravitational waves were first detected in 2015 using an experiment involving Laser Interferometer Gravitational Observatory (LIGO) detectors.
• But those waves were of high frequency and believed to have been produced by the merger of two relatively small black holes that took place about 1.3 billion years ago.
• Scientists have been looking for low-frequency gravitational waves for decades. They believed that such ripples are perpetually rolling through space like background noise.
• Pairs of supermassive black holes, sitting at the centre of galaxies, merge across the universe, generating gravitational waves. This breakthrough provides enough data to suggest that there is a gravitational wave background which exists in our universe.
• To discover low-frequency gravitational waves, scientists used entirely different technologies that were carried out by radio astronomers representing five different international teams, including Indian Pulsar Timing Array (InPTA).
• The researchers used six large radio telescopes around the world, including the one in Pune, to study objects called pulsars, distant rapidly-rotating neutron stars that emit pulses of radiation, observed from the Earth as bright flashes of light. 
• These bursts take place at exact intervals, and therefore scientists use pulsars as ‘cosmic clocks.
• After examining 25 pulsars over 15 years, Scientists have proposed that the observed inconsistencies were due to deformities caused in space-time by gravitational waves. These irregularities showed consistent effects of the presence of gravitational waves.

About LIGO:

• LIGO is an international network of laboratories that detect the ripples (gravitational waves) in space-time produced by the movement of large celestial objects like stars and planets. 
• These ripples were first postulated in Albert Einstein’s general theory of relativity, which encapsulates our current understanding of how gravitation works. 
• The LIGO detectors are sensitive to distance changes that are several orders of magnitude smaller than the length of a proton.
• The experiment works by releasing light rays simultaneously in both chambers. Usually, the light should return at the same time in both chambers. 
• However, if a gravitational wave passes through, one chamber elongates while the other squishes, resulting in a phase difference in the returning light rays. Detecting this phase difference confirms the presence of a gravitational wave.

What is Space-time?

• In Special Theory of Relativity, Einstein proposed that space and time don’t exist as independent entities, combining the three dimensions (height, width and depth) of space and one dimension of time into a single four-dimensional continuum, known as space-time.