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May 27th 2019

How Gravitational Waves Will Help Decipher Mysteries of the Universe

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Deep in the universe, cataclysms are rattling the fabric of space and time. Massively accelerating events, such as colliding black holes, orbiting neutron stars, exploding stars and more, create gravitational waves that, like ripples from a stone tossed into a pond, radiate out from the source. Until recently, the existence of these features was only a theory put forth by Albert Einstein. He surmised that they were invisible and moved at the speed of light. In September 2015, scientists using extremely sensitive U.S.-based instruments, collectively called the Laser Interferometer Gravitational-Wave Observatory (LIGO), detected these ripples in spacetime for the first time. They were coming from two black holes that had crashed into each other about 1.3 billion years ago.

Shortly after the discovery, an Indian initiative in gravitational-wave observations was approved, and the country’s government committed to constructing a third advanced interferometer. It will be built in the country’s Hingoli District, on the opposite side of the globe from the U.S.-based detectors in Washington and Louisiana. The three-pronged network will greatly expand the area of sky scientists can search, increase the number of sources they can spot and allow them to triangulate incoming data from space to better pinpoint the location of highly energetic cosmic events, according to the California Institute of Technology. What they learn will open a new window on the universe and the past from which humans fundamentally arose.

Doing the Wave

Peering into space goes back millennia to when humans first looked up to the stars. They relied on visible light in the early days, observing objects with their eyes and through telescopes. Advances in technology eventually allowed scientists to study other energetic parts of the electromagnetic (EM) spectrum, including infrared, X-rays, radio waves, microwaves and more.

But gravitational waves are different. “They are as distinct from EM radiation as hearing is to vision,” reports Caltech. The information they carry isn’t comparable to anything else scientists currently have access to. For instance, unlike electromagnetic radiation, gravitational waves interact weakly with matter. This means they aren’t impeded by planets, stars, galaxies or other objects as they ripple across spacetime. As a result, the information they carry is free of the distortions commonplace in EM-based data.

New insights gleaned from the features can eventually explain two big mysteries in the universe: gravity and dark energy. Although gravity keeps planets in orbit and prevents objects on Earth from floating up into space, it’s not well understood. It’s the weakest force in the universe and is many billions of times weaker than the electromagnetic force that holds atoms together, according to Stanford University. How and why is still theoretical.

Dark energy is another enigma. Scientists theorize that it makes up 60 percent of space and is responsible for the expansion of the universe, according to NASA. (Dark matter makes up roughly 27 percent of space.) But scientists have never observed dark energy, and their theories remain unproven.

How LIGO Works

The interferometer instruments that make up LIGO need to be huge and extremely sensitive because these cosmic waves are so weak. They’re all shaped like an “L,” with each arm extending 2.5 miles. The arms are 10 feet wide and 12 feet tall, and house a steel vacuum tube that’s about four feet wide. Laser beams are shot down the vacuum tubes. When a wave passes over Earth, it squeezes and stretches spacetime, causing one of the beams to slightly lengthen and the other beam to shorten. Mirrors and sensors, including a photodetector, pick up the infinitesimal change, according to NASA.

Having more than one instrument increases the amount of data being gathered. Placing the instruments far apart improves the location detection accuracy. It’s analogous to finding an active mobile phone by using three different cellphone towers to ping the phone. As the signals propagate in concentric circles from the tower, they only intersect at one spot — the phone.

“LIGO India is out of the plane of the other three advanced gravitational-wave interferometers. Thus, it will help narrow down the on-sky location of the gravitational waves tremendously and give a big boost to the astronomers hunting for the light,” Mansi Kasliwal, assistant professor of astronomy and the leader of a LIGO effort at Caltech, said in a press release.

An Indian initiative in gravitational-wave observations will serve as the third advanced interferometer to pinpoint colossal accelerating objects. Certain vibrational signatures from the waves generated will provide clues to the type of cataclysms. Scientists have identified four unique fingerprints: continuous, such as those produced by neutron stars; compact binary inspiral, such as those from pairs of white dwarf stars, black holes, or neutron stars that are orbiting each other; stochastic, which are small, random waves; and burst, which define unexpected or surprising waves.

A Global Collaboration

Like all major scientific endeavors, LIGO-India will involve research teams from different cultural backgrounds and political values coming together for a common goal. A consortium of Indian research institutions will work closely with the LIGO Laboratory in the United States, and different interferometers in Australia, Germany and the United Kingdom.

A team of Indian scientists has already been collaborating with U.S.-based LIGO scientists, says Nature. According to Ajit Kembhavi, emeritus professor at IUCAA Pune and chair of the LIGO-India site-selection committee, India has a long tradition of research in general relativity, gravitational waves and data analysis.

New discoveries and insights are inevitable. Once LIGO scientists pinpoint the source of a great cataclysm, other scientists will point more conventional instruments in that direction. Telescopes, X-ray observers, and radio wave and microwave detectors will add more data and insight.

The project will likely also raise questions scientists haven’t thought to ask. “Any time you turn on some new type of telescope or microscope, you discover things you couldn’t anticipate,” LIGO Laboratory Executive Director David Reitze said in a press release. “So, while there will be certain sources of gravitational waves that we expect to see, the really exciting part is what we did not predict and what we did not expect to see.”

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