Pune’s GMRT becomes first Indian facility to detect gravitational waves

In a major scientific breakthrough, an international team of astronomers has announced the first direct evidence for the existence of ultra-low frequency gravitational waves, which are ripples in the fabric of space-time caused by the movement of massive objects in the universe. The team used observations of pulsars, which are rapidly spinning neutron stars that emit radio signals at regular intervals, to detect the subtle effects of these gravitational waves on the arrival time of the signals.

Among the six of the world's largest radio telescopes that participated in this groundbreaking discovery, India's Giant Metrewave Radio Telescope (GMRT) located near Pune played a key role. The GMRT is operated by the National Centre for Radio Astrophysics (NCRA), which is part of the Tata Institute of Fundamental Research (TIFR). The GMRT was recently upgraded to enhance its sensitivity and frequency range, making it a unique instrument for detecting nano-hertz gravitational waves.

What are gravitational waves and how are they detected?

Gravitational waves are disturbances in the curvature of space-time that propagate as waves, travelling outward from their source at the speed of light. They were predicted by Albert Einstein in his general theory of relativity in 1916, but were first directly detected in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US. LIGO detected gravitational waves from the merger of two black holes, each about 30 times the mass of the sun, creating ripples in space-time with a frequency of about 100 hertz (cycles per second).

However, there are other sources of gravitational waves that have much lower frequencies, such as pairs of supermassive black holes, each millions or billions of times the mass of the sun, orbiting each other in the centres of galaxies. These black hole binaries emit gravitational waves with frequencies in the range of nano-hertz (one billionth of a hertz), which are too low to be detected by LIGO or any other ground-based or space-based interferometer.

To detect these nano-hertz gravitational waves, astronomers use a different technique, called pulsar timing. Pulsars are extremely dense remnants of massive stars that have exploded as supernovae. They have strong magnetic fields and rotate very fast, emitting beams of radio waves from their poles. These beams sweep across the sky like lighthouses, and can be detected by radio telescopes on Earth as regular pulses of radio emission.

Pulsars act like cosmic clocks, keeping time with remarkable precision. By measuring the arrival time of their pulses over many years, astronomers can monitor any deviations from their expected pattern. If a gravitational wave passes between a pulsar and the Earth, it will cause a slight change in the distance between them, and hence a slight change in the arrival time of the pulses. This change will be different for different pulsars, depending on their position and orientation relative to the gravitational wave.

By comparing the arrival times of pulses from many pulsars distributed across the sky, astronomers can look for correlated signals that indicate the presence of gravitational waves. This technique is known as pulsar timing array (PTA), and requires long-term observations with sensitive radio telescopes.

How did GMRT contribute to this discovery?

The GMRT is one of the world's largest and most sensitive radio telescopes, consisting of 30 antennas spread over an area of 25 km near Pune. It operates at low radio frequencies, ranging from 50 MHz to 1450 MHz, which are ideal for observing pulsars. The GMRT was upgraded in 2019 to improve its performance and flexibility, making it capable of observing up to 10 pulsars simultaneously with high precision.

The GMRT is part of the Indian Pulsar Timing Array (InPTA), which is a collaboration of researchers from various institutes across India and Japan. The InPTA uses the GMRT to observe about 40 pulsars every month, collecting data for more than three years. The InPTA also collaborates with other international PTA projects, such as the European Pulsar Timing Array (EPTA), which uses five other radio telescopes in Europe.

The EPTA and InPTA jointly analysed data from six radio telescopes, including the GMRT, covering 25 years of pulsar observations. They found that the arrival times of pulses from different pulsars showed consistent deviations that could not be explained by any known noise sources or errors. These deviations matched the expected signature of nano-hertz gravitational waves coming from a population of supermassive black hole binaries in distant galaxies.

The results were published in two papers in The Astrophysical Journal Letters on June 29, 2023. The papers reported a statistical significance of 4.9 sigma for the detection of gravitational waves, which means that there is only a one in a million chance that the signal is a false positive. The papers also estimated the strength and frequency of the gravitational wave background, which is the combined effect of all the sources of gravitational waves in the universe.

The detection of nano-hertz gravitational waves is a milestone in the field of gravitational wave astronomy, as it opens a new window to explore the universe and its mysteries. It also demonstrates the power and potential of the GMRT and the InPTA, which are among the leading facilities in the world for this research. The GMRT is the first and only Indian facility to detect gravitational waves, and has made India proud with its contribution to this historic discovery.

Source: 

(1) Pune: GMRT in Pune first Indian institution to detect gravitational waves. https://www.punenow.com/post/pune-gmrt-in-pune-first-indian-institution-to-detect-gravitational-waves.

(2) Pune’s GMRT becomes first Indian facility to detect gravitational waves. https://www.msn.com/en-in/news/other/pune-s-gmrt-becomes-first-indian-facility-to-detect-gravitational-waves/ar-AA1dcozm.

(3) Pune’s GMRT becomes first Indian facility to detect gravitational waves. https://indianexpress.com/article/cities/pune/punes-gmrt-first-indian-facility-detect-gravitational-waves-8692416/.

(4) India’s largest radio telescope key to detecting the universe’s .... https://www.thehindu.com/sci-tech/science/giant-metrewave-radio-telescope-gmrt-india-gravitational-waves/article67026398.ece.

(5) Pune-based radio telescope helps detect universe’s vibrations. https://www.hindustantimes.com/cities/pune-news/punebased-radio-telescope-helps-detect-universe-s-vibrations-101688149086504.html.

FAQ's

Which waves are detected by GMRT?

The Giant Metrewave Radio Telescope (GMRT) is related to Detection of cosmic radio waves. Which of the following is not a research purpose? ... What term is used to describe tha phenomenon whereby newspapers can be read online radio stations accessed on digital televisions and mobile phones enable internet access?

In which Indian state is the giant Metrewave radio telescope GMRT located?

NEW DELHI, INDIA'S Giant Metrewave Radio Telescope (GMRT) was one of the world's six large telescopes that played a key role in finding the first direct evidence for the relentless vibrations of the fabric of the universe, caused by ultra-low frequency gravitational waves.

What is the information about GMRT telescope which is situated in Pune?

The Giant Metrewave Radio Telescope (GMRT), located near Narayangaon, Pune in India, is an array of thirty fully steerable parabolic radio telescopes of 45 metre diameter, observing at metre wavelengths. It is the largest and most sensitive radio telescope array in the world at low frequencies.

When was GMRT established?

Overview of the GMRT It was conceived and built under the supervision of Prof. Govind Swarup from 1984 to 1996.