India to Join Hunt for Gravitational Waves
Aerial photo of LIGO Livingston, Louisiana, showing all of one 2.5-mile-long (4 kilometers) arm and part of the other (off to the right). The visible arms are concrete structures that protect the vacuum tubes from the elements.
Credit: Caltech/MIT/LIGO Lab

India is on track to join the international effort to find ripples in the fabric of space-time.

On Feb. 17, the Indian Cabinet, chaired by Prime Minister Shri Narendra Modi, granted "in-principle approval" for the country to start building a gravitational-wave detector that will work in concert with the two detectors currently operating in the United States and a third detector set to come online in Italy. Scientists associated with the project said it is feasible that the project could come online as soon as 2023.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) made history on Feb. 11, when scientists with the project announced the first direct detection of gravitational waves, or ripples in the fabric of space. With LIGO-India assisting in the hunt, the instruments will be more sensitive to gravitational waves, and will be better equipped to pinpoint the location of the events that cause the gravitational waves, according to LIGO scientists. [Watch the LIGO documentary "LIGO, A Passion for Understanding"]

Gravitational waves are ripples in space, first predicted by Albert Einstein in 1916 and created by cataclysmic cosmic events, like two black holes colliding. Directly detecting gravitational waves for the first time was a watershed moment for physics and astrophysics. These ripples move through space itself, and cannot be blocked by interstellar dust or other physical barriers, unlike light. This property of gravitational waves means they can carry information from places that scientists cannot probe with traditional instruments, like the inside of two black holes or the interior of an exploding star.

The U.S. LIGO facilities detected gravitational waves from two black holes colliding in space. The facility was about to pinpoint the location of the event to within a 600 square degree area of the sky. (The full moon takes up about half a degree on the sky.) The VIRGO facility, located in Italy, will soon provide additional gravitational-wave data that will combine with LIGO's data to reduce that area significantly, and an additional facility in India would further improve on that, according to a statement from the California Institute of Technology, which operates LIGO together with the Massachusetts Institute of Technology.

LIGO must make extremely precise measurements in order to detect gravitational waves. Each of the U.S. facilities consists of two 2.5-mile-long (4 kilometers) "arms," and scientists look for the changes in the length of those arms caused by a passing gravitational wave stretching or compressing space itself. The change in distance is less than the diameter of a single atom. If the scientists were measuring the distance between the sun and the next nearest star — Alpha Centauri, about 4.3 light-years away — they would be measuring a change in distance of only about 4 microns, which is less than the width of a human hair, according to the statement.  

Because LIGO measures such tiny variations in the length of the two arms, it's helpful for scientists to compare the detections of the two facilities. A signal detected at one facility should also be detected at the other facility. Adding a detector in India will further confirm the detection of gravitational waves, LIGO scientists said at the Feb. 11 announcement. In addition, the scientists said they can also learn more about space-time ripples by measuring how long it takes for a gravitational wave to travel the distance between different facilities.

Significant work has already been done to make the LIGO-India project a reality, the statement said. LIGO scientists "have made dozens of trips to India to work with Indian colleagues." The three Indian institutes that would have "primary responsibility for construction and operation of LIGO India" are the Inter-University Centre for Astronomy and Astrophysics (IUCAA), the Raja Ramanna Centre for Advanced Technology (RRCAT), and the Institute for Plasma Research (IPR).  The project is managed by India's Department of Atomic Energy and Department of Science and Technology. The U.S. LIGO project is funded by the National Science Foundation (NSF).

Fleming Crim, assistant director for mathematical and physical sciences at NSF, said in the statement, "Because the science reward is so strong, NSF enthusiastically endorses the decision of the Indian government to proceed with authorizing funding for the LIGO-India project."

The LIGO-India instrument will share its design with the U.S. LIGO facilities.  

"We have built an exact copy of that instrument that can be used in the LIGO-India Observatory, ensuring that the new detector can both quickly come up to speed and match the U.S. detector performance," David Shoemaker, leader of the Advanced LIGO Project and director of the MIT LIGO Lab, said in the statement. [The Search for Gravitational Waves (Gallery)]

Fred Raab, head of the LIGO Hanford Observatory and LIGO Laboratory liaison for LIGO-India, said in the statement, "Together, we have identified an excellent site for the facilities and have transferred detailed LIGO drawings of the facilities and vacuum system to IPR, after adapting them for conditions in India."

In addition to helping LIGO pinpoint the location of gravitational-wave sources and confirming their detection, it could open up unexpected new avenues of gravitational-wave science, said David Reitze, executive director of LIGO and a Caltech research professor.

"Anytime you turn on some new type of telescope or microscope, you discover things you couldn't anticipate," Reitze said. "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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