Background hum of the universe heard, Pune astrophysics lab listens in

Background hum of the universe heard, Pune astrophysics lab listens in

Subject : Science and technology

Section: Space technology

Context:

• Scientists have picked up evidence to suggest that a multitude of gravitational waves are ever-present in any area of the universe, their combined effects constantly deforming and reshaping spacetime, and altering the motion and behaviour of every heavenly body.

Gravitational wave background and background humming:

• This multitude of gravitational waves is named ‘Gravitational wave background’.
• The gravitational waves were produced by the merger of blackholes or explosion of stars and can take millions of years, providing a steady supply of gravitational waves. And there are many such events happening all the time.
• So, there is a sort of gravitational wave background that exists all the time.
• The noisy presence of several such gravitational waves, each with different characteristics, is what is now being referred to as the ‘background hum’.

Disruption in signals of pulsars as evidence of Gravitational wave background:

• Radio astronomers representing the different teams including the Indian Pulsar Timing Array (InPTA) shared that a time aberration, or delay, was observed in the signals emerging from distant rapidly-rotating neutron stars called pulsars that are sometimes spinning more than 1000 times every second.
  • They are so named because they emit pulses of radiation, observed from Earth as bright flashes of light, at every rotation. The time period of these pulses of radiation is fixed and predictable, the reason why these neutron stars are called ‘cosmic clocks’.
• In order to detect gravitational wave signals, scientists studied several ultra-stable pulsar clocks randomly distributed across our Milky Way galaxy through six of the largest radio telescopes in the world, including GIRT.
• The arrival of these signals can be calculated accurately, but during experiments, it was observed that some of them arrived a little early while a few others were late, the discrepancies ranging in millionths of seconds.
• These irregularities showed consistent effects of the presence of gravitational waves.
• Scientists say that possible sources of these low-frequency gravitational waves could be colliding pair of very large, ‘monster’, black holes, millions of times bigger than our Sun.
• Such large black holes are usually found at the centres of galaxies.
• Gravitational waves originating from the collision or mergers of such black holes can have very large wavelengths, extending up to light years, and consequently, very low frequencies.
• In all, six of the world’s most powerful and large radio telescopes – uGMRT, Westerbork Synthesis Radio Telescope, Effelsberg Radio Telescope, Lovell Telescope, Nançay Radio Telescope and Sardinia Radio Telescope – were deployed to study 25 pulsars over a period of 15 years.
• In addition to data from these facilities, highly sensitive UGMRT data of more than three years were analysed too.
• It has been concluded that radio flashes from these pulsars were affected by the nano-hertz gravitational waves believed to emerge from ‘monster’ black holes.

Gravitational waves:

• Gravitational waves are ripples, or disturbances, produced in the fabric of spacetime by large moving objects.
• The existence of gravitational waves was predicted by Albert Einstein’s general theory of relativity more than a century ago, but its experimental confirmation came only in 2015.
  • As per the General Theory of relativity (1905) space and time were not independent entities but had to be woven together as spacetime.
• He also proposed that spacetime was not transparent, inert, static or fixed background to all the events in the universe. Instead, spacetime was flexible and malleable, interacted with matter, was influenced by it, and in turn, influenced the events that take place there.

Gravitational wave detection:

• In 2015, scientists detected gravitational waves for the first time through LIGO (Laser Interferometer Gravitational-wave Observatory) detectors.
• Those waves were produced by the merger of two black holes that took place about 1.3 billion years ago.
• But scientists contend that such events, mergers of black holes or explosions of stars, keep happening all the time, regularly producing gravitational waves. Even the simple motion of large bodies can produce detectable gravitational waves.
  • Only the waves produced just ahead of the merger, when the energy released was maximum, could be detected.

LIGO India Project:

• LIGO is an international network of laboratories that detect the ripples in spacetime produced by the movement of large celestial objects like stars and planets.
• LIGO-India will be located in Hingoli district of Maharashtra, about 450 km east of Mumbai, and is scheduled to begin scientific runs from 2030.

LIGO (Laser Interferometer Gravitational-Wave Observatory):

• It is an international network of laboratories meant to detect gravitational waves.
• Under this, two large observatories (~ 3000 Km apart) were built in the US (Hanford Site, Washington and Livingston, Louisiana) with the aim of detecting gravitational waves by laser interferometry.
• Interferometry is a technique which uses the interference of superimposed waves to extract information.
• Besides the US, such gravitational wave observatories are currently operational in Europe and Japan.

LIGO-India will be the fifth, and possibly the final node of the planned network.