Why in news?

• Recently, an international team of astronomers announced scientific evidence confirming the presence of gravitational waves using pulsar observations.
• India’s Giant Metrewave Radio Telescope (GMRT) was among the world’s six large telescopes that played a vital role in providing this evidence.

What’s in today’s article?

• Giant Metrewave Radio Telescope (GMRT)
• Gravitational waves

Giant Metrewave Radio Telescope (GMRT)

• GMRT is a low-frequency radio telescope that helps investigate various radio astrophysical problems ranging from nearby solar systems to the edge of the observable universe.
• Located at Khodad, 80 km north of Pune, the telescope is operated by the National Centre of Radio Astrophysics (NCRA).
  • NCRA is a part of the Tata Institute of Fundamental Research (TIFR), Mumbai.
  • GMRT is a project of the Department of Atomic Energy (DAE), operating under the Tata Institute of Fundamental Research (TIFR).
• It consists of 30 fully- steerable dish type antennas of 45-meter diameter each, spread over a 25-km region.
  • GMRT is presently the world’s largest radio telescope operating at meter wavelength.

Objectives of GMRT

• GMRT is a very versatile instrument for investigating a variety of radio astrophysical problems. Two of its most important astrophysical objectives are:
  • to detect the highly redshifted spectral line of neutral Hydrogen expected from proto-clusters or protogalaxies before they condensed to form galaxies in the early phase of the Universe;
    • Redshift represents the signal’s wavelength change depending on the object’s location and movement.
  • to search for and study rapidly-rotating Pulsars in our galaxy.
    • Pulsars are rapidly rotating neutron stars with extremely high densities.
    • A pulsar is like a cosmic lighthouse as it emits radio beams that flashes by the Earth regularly akin to a harbour lighthouse.

Significance of GMRT

• Highly sought-after telescope
  • GMRT is a unique facility functioning within the frequency bandwidth of 100 Mhz-1,500 MHz.
  • It is a highly sought-after telescope both within India and by scientists from 30-plus countries.
• Understanding the evolution of galaxies over cosmic time
  • Understanding the evolution of galaxies over cosmic time requires tracing the evolution of neutral gas at different cosmological periods.
    • Atomic hydrogen is the basic fuel required for star formation in a galaxy.
    • When hot ionised gas from the surrounding medium of a galaxy falls onto the universe, the gas cools and forms atomic hydrogen.
    • This then becomes molecular hydrogen and eventually leads to the formation of stars.
    • Atomic hydrogen emits radio waves of 21 cm wavelength, meaning the wavelength is a direct tracer of the atomic gas content in nearby and distant galaxies.
  • However, this radio signal is feeble and nearly impossible to detect the emission from a distant galaxy.
  • Using GMRT data, scientists detect signal that was emitted from a distant galaxy.
• Galactic and extragalactic radio sources
  • Because of its large collecting area and wide frequency coverage, GMRT is an useful instrument for studying many other problems at the frontiers of astrophysics.
  • These include studies of Solar and planetary radio emissions; relationship between Solar activity and disturbances in the interplanetary medium etc.

Gravitational Waves

• About
  • Gravitational waves are ripples in space-time caused by some of the most violent and energetic processes in the Universe.
  • Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity.
  • Einstein's mathematics showed that massive accelerating objects would disrupt space-time in such a way that waves of undulating space-time would propagate in all directions away from the source.
    • These massive objects include things like neutron stars or black holes orbiting each other.
  • These cosmic ripples would travel at the speed of light, carrying with them information about their origins, as well as clues to the nature of gravity itself.
• Production of gravitational waves
  • The strongest gravitational waves are produced by cataclysmic events such as colliding black holes, supernovae (massive stars exploding at the end of their lifetimes), and colliding neutron stars.
  • Other gravitational waves are predicted to be caused by the rotation of neutron stars that are not perfect spheres, and possibly even the remnants of gravitational radiation created by the Big Bang.
• Feature
  • Gravitational waves are incredibly weak and difficult to detect because they interact very weakly with matter.
  • However, extremely sensitive instruments called interferometers have been developed to detect these waves.
  • The most famous example is the Laser Interferometer Gravitational-Wave Observatory (LIGO), which made the first direct detection of gravitational waves in 2015.

News Summary: India’s largest radio telescope plays vital role in detecting universe’s vibrations

• Two different studies were published recently by radio astronomers representing the Indian Pulsar Timing Array (InPTA) and European Pulsar Timing Array (EPTA).
• These studies shared that a time aberration was observed in the signals emerging from these pulsars.

Analysing the signals from pulsars

• Why these signals are of great interest among scientists?
  • Nicknamed as cosmic clocks, pulsars are rapidly spinning neutron stars that send out radio signals at regular intervals which are seen as bright flashes from the Earth.
  • As these signals are accurately timed, there is a great interest in studying these pulsars and to unravel the mysteries of the Universe.
• How analysis is done?
  • In order to detect gravitational wave signals, scientists explore several ultra-stable pulsar clocks randomly distributed across our Milky Way galaxy and create an ‘imaginary’ galactic-scale gravitational wave detector.
  • There are several signals travelling through spacetime of the Universe.
  • But, the presence of gravitational waves influences the arrival of these signals when detected from Earth.
    • It was noticed that some signals arrive early while others, with a slight delay (less than a millionth of a second).
• What has been detected?
  • Nano-hertz signals were heard as humming from the Universe.
    • It is expected that ultra-low frequency gravitational waves, also known as nano-hertz gravitational waves, emerge from a colliding pair of very large monster black holes, many crores of times heavier than our Sun.
    • The signals or ripples that emerge from within these blackholes are known as nano-hertz gravitational waves.
    • Their wavelengths can be many lakhs of crores of kilometres and oscillate with a periodicity anywhere between a 1 year to 10 years.
    • When there is continuous arrival of these nano-hertz gravitational waves, it creates a consistent humming in our Universe, which gets detected using powerful radio telescopes from the Earth.
  • These were caused due to the presence of gravitational waves and due to signal irregularities emerging from pulsars.