From “Science Magazine” : “In India train tracks threaten a giant telescope”

From “Science Magazine”

3.7.23
Sanjay Kumar

For nearly 30 years, the Giant Metrewave Radio Telescope (GMRT) here 200 kilometers east of Mumbai has listened for faint low-frequency radio signals emanating from the distant reaches of the cosmos. Its Y-shaped network of 30 antennas, each 45 meters wide, spreads over 25 square kilometers. The dishes have helped astronomers from dozens of nations study some of the most distant known galaxies and one of the universe’s biggest known explosions, an outburst from a giant black hole in the Ophiuchus Supercluster. The telescope is among the most sensitive in the world at these low frequencies, but it could soon be deafened by signals emanating from a mundane source: electric trains.

Last month, the Indian government gave approval “in principle” for construction of a pair of high-speed rail lines that would slice through the GMRT’s array, edging within 960 meters of some antennas. By 2026, planners envision 48 electric passenger trains, as well as cargo haulers, plying the tracks each day as they travel some 235 kilometers between the cities of Pune and Nashik.

That prospect has astronomers very worried. “The key villain here is the pantograph, which is perched on top of the rail engine, constantly touching the overhead high-tension power line to draw electricity to propel the train,” says Yashwant Gupta, director of the National Centre for Radio Astrophysics, a division of the Tata Institute of Fundamental Research, which operates the GMRT. As the pantograph makes and breaks contact with the line, he says, it produces sparks and electromagnetic bursts that can “drown the entire spectrum of faint radio signals the telescope is devoted to study.” Railway communications equipment can add to the interference, Gupta notes, making it impossible for the GMRT to detect signals within its listening range of 100 to 1450 megahertz.

To protect the telescope, astronomers are asking planners to consider rerouting the railway or placing the tracks and equipment inside tunnels. “We would like to coexist,” Gupta says, but the lines “should be taken at least 15 to 20 kilometers away from the GMRT to minimize radio interference.”

Rail project officials declined to comment on the astronomers’ concerns. But local politicians have long been outspoken in their support for the project. Amol Kolhe, who represents the region in Parliament, says although the GMRT is a source of scientific pride, the need to protect it from electromagnetic interference has held back the region’s economy. “Scientific projects should not come in the way of development,” he says, predicting that if “the railway project is stalled or significantly compromised, there definitely will be agitations” among his constituents, many of whom support the project.

At the root of the impasse is India’s rapid economic development. When astronomers selected the GMRT site in 1990, it was sparsely populated and surrounding hills protected it from electromagnetic smog produced by distant urban areas. Over time, however, nearby communities have grown, bringing with them many technologies that produce radio signals, including power lines, lights, engines, cellular networks, and even mosquito-killing devices.

Today, the GMRT is one of the few radio telescopes located in a densely populated region, and its staff go to enormous lengths to protect it from disruptive signals. Researchers carefully track possible sources of interference within 30 kilometers of the telescope, and periodically venture into communities to work with businesses, farmers, and others to alter equipment or practices to reduce problematic noise. Because of restrictions, “even mobile phones came late to the area,” Kolhe says.

Still, GMRT officials argue its presence has not harmed the local economy. Gupta notes his center has over the years signed off on the launch of more than 2000 businesses in the area, including two sugar processing mills. And it has worked with mobile phone companies, wind turbine operators, and India’s air force to resolve potential conflicts.

Despite its age and the arrival of newer radio telescopes, astronomers say the GMRT still has a role to play in research. In particular, it can listen for the faint hum produced by the clouds of electrically neutral hydrogen atoms that existed in the early universe. The telescope “is making important contributions by surveying for neutral hydrogen,” which provides clues to the evolution of stars and galaxies, says physicist Jacqueline Hewitt of the Massachusetts Institute of Technology. “The GMRT still has a unique place among the radio telescopes available to the community,” says astronomer Raffaella Morganti of the Kapteyn Astronomical Institute at the University of Groningen.

Gupta and other astronomers are hoping they can find a way for the telescope and the railway line to coexist. Some say they are frustrated that, so far, rail officials have declined to engage in discussions while pushing the government to produce final approvals. Others worry that, with several major elections looming, elected officials will be reluctant to delay or redesign the project.

Kolhe, however, says he is “open to all the ideas for solution.” And Gupta hopes substantive talks will start soon. “This is a very good time for us to get into detailed discussions” about how to allow trains to start rolling on Earth without drowning out the sounds of the cosmos.

See the full article here .

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