Explained: Gravitational waves and the cosmic 'background hum'

 Astronomers used a galaxy-sized antenna of millisecond pulsars in the Milky Way to spot low-frequency gravitational waves for the first time in history. The "background hum" is rumbling throughout the universe and it is the first evidence of a long-theorised form of gravitational waves. 

This becomes a notable event in the history of astrophysics - all thanks to the breakthrough made by hundreds of scientists using radio telescopes in North America, Europe, China, India and Australia after years of work. 

The day has been hailed as a major milestone that opens a new window into the universe as it comes around eight years after scientists spotted the elusive ripples in space-time. 

What are gravitational waves? 

Astrophysicists have previously stated that gravitational waves are 'ripples' in space-time created by some of the universe's most destructive and intense activities. It is also an attestation of what Albert Einstein had predicted in 1916, in his general theory of relativity. 

Theory of relativity

Einstein's theories are said to be one of the most important papers ever published in the field of physics. In layman's terms, the theory of relativity consists of two interrelated physics theories; special relativity and general relativity. Special relativity applies to all physical phenomena in the absence of gravity. 

Meanwhile, general relativity describes the law of gravitation and its relationship to natural forces. It applies to cosmology and astrophysics, especially astronomy.  

The general theory of relativity is a major building block of modern physics and is related to gravity, which is one of the fundamental forces in the universe. 

It basically talks about the force of gravity and how it arises from the curvature of space and time. Well, an elaborated mathematical formula is followed, which is for the experts, not us. We need to understand the latest announcement

What do we know about the latest finding? 

As mentioned earlier, gravitational waves are ripples in the fabric of the universe that travel through everything at the speed of light almost entirely unimpeded. However, their existence was not confirmed until 2015, when the US and Italian observatories detected the first gravitational waves created by two black holes colliding. 

These "high-frequency" waves were caused by a single explosive event that sent a powerful, brief burst rippling towards Earth. However, scientists have been looking for low-frequency gravitational waves, which are considered to be constantly rolling across space like background noise, for decades. 

To know more about the phenomenon, scientists joined forces under the banner of the International Pulsar Timing Array consortium and worked at gravitational wave detectors on several continents. They finally revealed on Thursday that they have found strong evidence of these background waves.

 As quoted by the news agency Reuters, Oregon State University astrophysicist Xavier Siemens said, "As gravitational waves pass through the galaxy, they stretch and they squeeze it. And then these times of arrival of these pulses are changed. So one pulsar, as it's approaching the earth, its pulses will arrive a little earlier than we expect, as other pulsars will be away from the earth because it's being affected by the gravitational wave and those pulses arrive a little later." 

Siemens is a co-director of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a collaboration of more than 190 scientists from the United States and Canada who worked to monitor the gravitational wave signals. 

Gravitational waves, as well as ghostly subatomic particles known as neutrinos, allow for a more thorough exploration of the universe. Seven years ago, physicists revealed that the gravitational waves were generated by two distant black holes - extremely compact objects with gravity so powerful that not even light can escape. Gravitational waves can be caused by the motion of black holes and other enormous objects. 

Siemens told Reuters, "So if you imagine, you know, the collection of supermassive black holes that were that, you know, we were seeing correlations for as kind of like a choir or an orchestra... Imagine one of these orchestra members is a little bit close or is playing a little bit louder for some reason. That only happens with supermassive black holes." 

How did scientists carry out the research? 

Scientists issued radio telescopes around the world, which were aimed at a total of 115 pulsars throughout the Milky Way, to carry out the new research. 

Scientists then measured the incredibly small differences in the timing of the pulses, searching for the signs of gravitational waves. French astrophysicist Antoine Petiteau said they were able to "detect changes of less than one-millionth of a second across more than 20 years". 

Maura McLaughlin of the US Pulsar Search Collaboratory programme said they were "awestruck" after first seeing evidence of the waves in 2020. During the press conference, she said that it was "really a magical moment". 

According to Siemens, the data would be able to help scientists map out how galaxies form over time. He said, "I am surprised that we were able to (do this) in some ways because it's a little bit of a long shot. And I think another part of the surprise is the amplitude of the signal is actually a little bit larger than we expected." 

International Conference on Gravitational Waves

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