What are Gravitational Waves?

What’s in today’s article?

• Why in News?
• What are Gravitational Waves?
• Why is the Detection of Gravitational Waves Important?
• How were Low-frequency Gravitational Waves Detected?
• Why is Discovery Important?

Why in News?

• Scientists have found evidence to suggest that the universe is filled with low-frequency gravitational waves.
• They have also contended that these waves create a cosmic background hum (which they could hear), that permeates outer space.

What are Gravitational Waves?

• These are ripples in the fabric of space-time that are created by huge objects moving around, colliding, and merging with each other.
• They were predicted by Albert Einstein’s General Theory of Relativity more than 100 years ago and were first detected in 2015 using an experiment involving Laser Interferometer Gravitational Observatory (LIGO) detectors.
  • In his General Relativity Theory, Einstein proposed that gravitational attraction was a result of the bending of the fabric of spacetime by the equivalent of a heavy object.
  • This is very often elucidated by an animation in which a large ball is placed on a rubber sheet, creating a curvature in the sheet.
  • When a smaller ball is rolled on the rubber sheet, it moves around the large ball along the curvature for a while before falling into it.
  • Einstein said the Sun, the Earth and all other bodies formed similar curvatures around them, and this was the reason for smaller objects getting pulled towards them.
  • But since the Earth, sun and everything else are also moving, the curvature around them moves too.
  • This creates ripples in spacetime (called gravitational waves), just like a moving boat in water creates ripples.
• The experiment detected waves of high frequency, believed to be produced by the merger of two relatively small black holes that took place about 1.3 billion years ago.
• All the subsequent detections after that were also of high-frequency waves. This, however, has changed now.

Why is the Detection of Gravitational Waves Important?

• Everything that is known about faraway objects has come through the detection of the electromagnetic waves either emitted or reflected by them.
• These electromagnetic waves (of which visible light is also a part) very often carry information that is characteristic of the objects they are emitted by.
• However, ~95% of the universe is known to consist of dark matter and dark energy, which don’t emit any light or any other electromagnetic waves.
• Hence, most of the cosmos remains ‘invisible’ to astrophysicists and astronomers.
• This changed with the detection of the gravitational waves, which can tell about origin and answer fundamental questions about outer space, such as how different galaxies have emerged and evolved over the entire course of the universe.

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How were Low-frequency Gravitational Waves Detected?

• Like a whole spectrum of electromagnetic waves, from microwaves to radio waves, there is a wide range of gravitational waves of different wavelengths, frequencies and energies.
• The gravitational wave that was detected in 2015, and all subsequent detections after that, involved mergers of black holes that were relatively small in size. The gravitational waves produced by them are relatively feeble.
• Only the waves produced just ahead of the merger, when the energy released was maximum, could be detected. These are like flashes of gravitational waves, lasting for maybe a few milliseconds
• In a bid to discover low-frequency gravitational waves, scientists used an entirely different technology.
• 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 extremely precise intervals, and therefore scientists use pulsars as ‘cosmic clocks’.
  • Some of the signals from these neutron stars arrived a little early while a few others were late, the discrepancies ranging in millionths of seconds.

Why is Discovery Important?

• Scientists have been looking for low-frequency gravitational waves for decades.
• They believed that such ripples are perpetually rolling through space like background noise.
• The latest breakthrough provides enough data to suggest that there is a gravitational wave background, which exists in our universe.
• The discovery will help scientists expand their knowledge about the nature and evolution of the universe.
• It will also help them gain more information about the environment around massive black holes.

Q1) What is LIGO?

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves. Two large observatories were built in the US with the aim of detecting gravitational waves by laser interferometry.

Q2) What is Albert Einstein’s General Theory of Relativity?

Einstein’s 1915 general theory of relativity holds that what we perceive as the force of gravity arises from the curvature of space and time. The scientist proposed that objects such as the sun and the Earth change this geometry.

Source: Scientists detect the universe’s ‘noisy’ gravitational wave background: What it means and why you should care about it