Scientists on Thursday said they have for the first time detected gravitational waves hypothesised by physicist Albert Einstein a century ago, in a landmark discovery that opens a new window for studying the cosmos.
The researchers said they detected gravitational waves coming from two black holes — extraordinarily dense objects whose existence also was foreseen by Einstein — that orbited one another, spiralled inward and smashed together. They said the waves were the product
of a collision between two black holes 30 times as massive as the Sun, located 1.3 billion light years from Earth.
The scientific milestone, announced at a news conference in Washington, was achieved using a pair of giant laser detectors in the United States, located in Louisiana and Washington State, capping a long quest to confirm the existence of these waves.
The announcement was made in Washington by scientists from the California Institute of Technology, the Massachusetts Institute of Technology and the LIGO Scientific Collaboration.
Detecting the gravitational waves required measuring 2.5 mile or 4 km laser beams to a precision 10,000 times smaller than a proton.
The two laser instruments, which work in unison, are known as the Laser Interferometer Gravitational-Wave Observatory (LIGO). They are able to detect remarkably small vibrations from passing gravitational waves. After detecting the gravitational wave signal, the scientists said they converted it into audio waves and were able to listen to the sounds of the two black holes merging.
"We're actually hearing them go thump in the night," MIT physicist Matthew Evans said. "We're getting a signal which arrives at Earth, and we can put it on a speaker, and we can hear these black holes go, 'Whoop.' There's a very visceral connection to this observation."
The scientists said they first detected the gravitational waves last September 14.
"We are really witnessing the opening of a new tool for doing astronomy," MIT astrophysicist Nergis Mavalvala said in an interview. "We have turned on a new sense. We have been able to see and now we will be able to hear as well."
Einstein in 1916 proposed the existence of gravitational waves as an outgrowth of his ground-breaking general theory of relativity, which depicted gravity as a distortion of space and time triggered by the presence of matter.
But until now scientists had found only indirect evidence of their existence.
‘Opens a new window’
Scientists said gravitational waves open a door for a new way to observe the universe and gain knowledge about enigmatic objects like black holes and neutron stars. By studying gravitational waves they also hope to gain insight into the nature of the very early universe, which has remained mysterious.
Everything we know about the cosmos stems from electromagnetic waves such as radio waves, visible light, infrared light, X-rays and gamma rays. But because such waves encounter interference as they travel across the universe, they can tell only part of the story.
Gravitational waves experience no such barriers, meaning they can offer a wealth of additional information. Black holes, for example, do not emit light, radio waves and the like, but can be studied via gravitational waves.
"It is really a truly, truly exciting event," said Abhay Ashtekar, director of Penn State University's Institute for Gravitation and the Cosmos. "It opens a brand new window on the universe."
"The LIGO announcement describes one of the greatest scientific discoveries of the past 50 years," Cornell University physicist Saul Teukolsky added.
The detection of gravitational waves already has provided unique insight into black holes, with the scientists saying it has demonstrated that there are plenty of black holes in the range of tens of solar masses, resolving the long debated issue of the existence of black holes of that size.
GRAVITATIONAL WAVES EXPLAINED
What are gravitational waves?
Gravitational waves are small ripples in space-time that are believed to travel across the universe at the speed of light. They are like tiny waves on a lake — from far away, the lake’s surface looks glassy smooth; only up very close can the details of the surface be seen. They were predicted to exist by Albert Einstein in 1916 as a consequence of his General Theory of Relativity.
What does Einstein say about gravity?
While Sir Isaac Newton visualised gravitational force as a pulling force between objects, Albert Einstein opined it to be a pushing force due to the curvature of four dimensional spacetime fabric. The curvature of spacetime stems from the dent heavy objects produce on spacetime fabric, which can be compared to the dent one could see on a plastic sheet when a massive ball is placed.
How are these waves detected?
Scientists have been trying to detect them using two large laser instruments in the United States, known together as the Laser Interferometer Gravitational-Wave Observatory (LIGO), as well as another in Italy.
The twin LIGO installations are located roughly 3,000 km apart in Livingston, Louisiana, and Hanford, Washington. Having two detectors is a way to sift out terrestrial rumblings, such as traffic and earthquakes, from the faint ripples of space itself.
The LIGO work is funded by the National Science Foundation, an independent agency of the U.S. government.
Why is the study of gravitational waves important?
Discovery of gravitational waves would represent a scientific landmark, opening the door to an entirely new way to observe the cosmos and unlock secrets about the early universe and mysterious objects like black holes and neutron stars.
Did scientists ever detect gravitational waves?
Although, physics supports the existence of gravitational waves, the strength of such waves even due to astronomically heavy bodies is awfully weak to be detected.
On March 17, 2014, Harvard-Smithsonian Centre for Astrophysics erroneously claimed discovery of gravitational waves. The Harvard group, working at BICEP2 (Background Imaging of Cosmic Extragalactic Polarisation) telescope, had reported that they had observed a twist in the polarisation of ancient light that goes back to the time of the big bang. But within a month, studies pointed out flaws in the study.
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