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eight years later First ever discovery of gravitational wavesAn achievement that was honored by the Nobel Prize for Physics two years later, scientists have now gathered evidence indicating the existence of a large number of gravitational waves in any region of the universe, and their combined effects constantly distort and reshape space-time, and change the motion and behavior of every celestial body.
This can be a common analogy. When a stone is dropped into a lake, it produces short-lived ripples in the water. But when raindrops fall on the lake, each drop forms a wave. These waves interact with each other, and the disturbance on the surface of the lake is the combined effect of all these individual waves. An object floating on the lake, say a paper boat, will experience and be affected by the combined effect of all these waves. Also, compared to a single drop of stone, disturbances from precipitation last longer. Something similar is happening in the universe. A large number of gravitational waves, generated by various events, are constantly distorting space-time. All celestial bodies, like Earth, move under the influence of this combined effect, said Yashwant Gupta, director of the National Center for Radio Astronomy (NCRA) based in Pune. .
Evidence for the so-called “gravitational-wave background” was captured using a completely different technique compared to that used in the first detection of gravitational waves in 2015. Six large radio telescopes around the world, including the giant wave in Pune. A radio telescope operated by NCRA has measured very small delays — on the order of millionths of a second — in the signals coming from distant, rapidly spinning stars called pulsars. Scientists suggest that these delays were the result of distortions in space-time caused by gravitational waves.
Gravitational waves are ripples, or disturbances, produced in the fabric of space-time by large moving objects, something similar to ripples produced on the surface of water by a moving boat. The existence of gravitational waves was predicted by Albert Einstein’s general theory of relativity more than a century ago, but their experimental confirmation only came in 2015.
Having shown, in 1905, that space and time are not independent entities but must be woven together as spacetime, Einstein proposed, in his general theory of relativity in 1915, that spacetime was not merely a transparent, inert, static or immutable background. to all events in the universe. Instead, space-time was fluid and elastic, interacting with matter, being affected by it, and in turn affecting the events that occurred there. It was like a soft cloth responding and being deformed by something heavy being placed on it.
In 2015, scientists detected gravitational waves for the first time with the LIGO (Laser Interferometer Gravitational-Wave Observatory) instruments. These waves were caused by the merger of two black holes that occurred about 1.3 billion years ago. But scientists maintain that such events, mergers of black holes or exploding stars, continue to occur all the time, regularly producing gravitational waves. Even simple motion of large objects can produce detectable gravitational waves.
“Just as you have the full spectrum of electromagnetic waves, from microwaves to radio waves, you can have a wide range of gravitational waves of different wavelengths, frequencies, and energies. The gravitational wave discovery in 2015, and all subsequent detections thereafter, have involved black hole mergers.” They were relatively small in size. The gravitational waves they produce are relatively weak. Only waves produced just before the merger, when the energy released was at its maximum, can be detected. Somak Raychaudhury, Vice Chancellor of Ashoka University, former director of the Inter-University Center for Astronomy and Astrophysics ( IUCAA) in Pune, these are like flashes of gravitational waves, lasting maybe a few milliseconds.
“There are more massive black holes that are constantly merging, and black holes millions or billions of times more massive than our Sun are usually in the center of galaxies. They can produce gravitational waves that can be detected from many times before they merge. In fact, the merger process can take millions of years, providing a supply of A constant of gravitational waves. And there are many such events happening all the time. So, there is a kind of background of gravitational waves that is there all the time.”
The “loud” presence of many of these gravitational waves, each with different properties, is what is now referred to as “background hum”. The results were announced simultaneously on Thursday by five international teams, including the one based in Pune.
The latest breakthrough is expected to help scientists better understand the nature and evolution of the universe.
“We do not yet say that we have been able to prove the existence of a gravitational wave background, because the level of confidence for this assertion is not very high. But we have produced very promising data that point in this direction. Ultimately, we should be able to separate the signals of large single events that produce Strong gravitational waves are the current symphony of signals we’re looking at. Because these are markers of large-scale interactions in the universe, we can gain information about the large-scale structure of the universe, its evolutionary history and the dynamics of events such as galaxy mergers,” said NCRA’s Gupta.
In various studies published Thursday, radio astronomers representing various teams including the Indian Pulsar Timing Array (InPTA) shared that a time drift, or delay, has been observed in the signals originating from distant, fast-spinning neutron stars called pulsars that orbit Sometimes more. more than 1000 times every second. It is so named because it emits pulses of radiation, observed from Earth as bright flashes of light, on each cycle. The time period of these pulses of radiation is constant and predictable, the reason why these neutron stars are called “cosmic clocks”.
In order to detect gravitational wave signals, scientists studied several superstable pulsars randomly distributed across our Milky Way galaxy through six of the world’s largest radio telescopes, including GMRT. The arrival of these signals can be accurately calculated, but during the experiments it was observed that some of them arrived a little early while others were delayed, and the discrepancies ranged in parts of a millionth of a second.
“These irregularities showed consistent effects of the presence of gravitational waves,” said Bhal Chandra Joshi, NCRA’s chief scientist and the man behind InPTA.
Scientists say the possible sources of these low-frequency gravitational waves could be colliding with a pair of very large, “monstrous” black holes, millions of times more massive than our sun. Such large black holes are usually found in the centers of galaxies. Gravitational waves arising from the collision or merger of such black holes can have very large wavelengths, extending up to light years, and therefore very low frequencies.
In all, six of the world’s most powerful and largest radio telescopes — uGMRT, Westerbork Synthesis Radio Telescope, Effelsberg Radio Telescope, Lovell Telescope, Nançay Radio Telescope and Sardinia Radio Telescope — have been deployed to study 25 pulsars over the course of 15 years. In addition to data from these facilities, more than three years of highly sensitive uGMRT data were also analyzed. He concluded that the radio flashes from these pulsars were affected by the nanohertz gravitational waves that are thought to emanate from “monster” black holes.
Along with scientists from NCRA, InPTA includes experts from Indian Institute of Science Education and Research, Bhopal, Raman Research Institute (RRI), Bengaluru, IIT-Roorkee, IIT-Hyderabad, Institute of Mathematical Sciences, Chennai.
Although the Laser Interferometer Gravitational Observatory (LIGO) captured these waves that lasted a few seconds, the PTAs observed these signals in a different frequency range.
“But a galaxy-sized PTA can sense the perpetual vibration of the gravitational-wave background at nanohertz frequencies,” said Professor A. Gopakumar of the Tata Institute of Fundamental Research (TIFR) in Mumbai.
NCRA’s Joshi said Einstein’s theory predicted that gravitational waves would change the arrival times of these radio flashes, thus affecting the measured ticks of our cosmic clocks.
Because these changes are small, astronomers need sensitive telescopes like uGMRT and an array of radio pulsars to separate these changes from other disturbances. Such slow signal variations mean that it takes decades to search for the elusive nanohertz gravitational signals.”
Professor Michael Kramer, Director of the Max Planck Institute in Germany, who is also a collaborator, called the international collaborative effort scientifically rewarding. “We hope to serve as a role model for the International Pulsar Timing Array effort,” he said.
With inputs from Partha Biswas in Pune
(Anjali Marar is with Raman Research Institute, Bengaluru)
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