New Delhi :

Anuradha Samajdar, a research scholar in Calcutta, initially thought the first email alert she received about a possible gravitational wave signal was a “blind injection”, the community jargon for a simulation, a trick to test the integrity of the data analysis process.

The email was from Marco Drago, a scientist at the Max Planck Institute for Gravitational Physics, Hannover, Germany, telling a global consortium of physicists that two giant instruments on Earth had sensed (for just a fleeting one-fifth of a second) a signal.

The arrays of lasers, mirrors and control electronics that make up the detectors of the Laser Interferometer Gravitational Wave Observatory (Ligo), located 3,000km apart in the US, had recorded what appeared to be ripples in space-time – possibly the first direct observation of gravitational waves.

It would be up to the data analysis groups scattered across the world, including in Bangalore, Calcutta, Gandhinagar, Pune and Thiruvananthapuram, to determine that they were genuine effects of gravitational waves – and not just noise from the cosmos masquerading as gravitational waves.

“I had heard about blind injections – where a very select few senior scientists release signals and data analysis teams work on them only to be told later that this was a test,” said Samajdar, a scholar working towards her PhD at the Indian Institute of Science Education and Research, Calcutta.

Drago, an Italian and a member of the Ligo consortium, was among the first scientists to be alerted that something interesting had been turned up by an automatic “pipeline” that scans and filters the signals picked up by the detectors.

Shortly before noon on September 14, Drago received the automated pipeline alert. “The signal was so nice, so perfect, it looked like it was coming from a binary (a pair of objects),” Drago told The Telegraph .

After telephone consultations with colleagues, he sent out the alert to the 900-odd consortium members.

Samajdar and physicist Rajesh Nayak at IISER were among scientists in India analysing the signals, trying to determine whether the patterns of ripples observed indeed matched theoretical predictions of what patterns would look like, depending on the source of the gravitational waves.

Nayak, a faculty member at the IISER department of physical sciences, said: “We first match the detected signal pattern with the theoretical predicted pattern, if there is a match, we try and use the signal to estimate various parameters of the source event.”

Supervised by Nayak, Samajdar, who graduated in physics from the Lady Brabourne College, Calcutta, before joining IISER’s integrated PhD programme, while still a bit sceptical about the nature of the signal, began the process of extracting information about the source.

“We began to calculate the masses of the (merging) black holes, their distance – and our estimates were similar to what others in the consortium were reporting,” Samajdar said. “We told ourselves noise wouldn’t give us such nice outputs – that’s when I wondered ‘is this really the big thing’?”

Scientists at the Inter-University Centre for Astronomy and Astrophysics, Pune, the Indian Institute of Technology, Gandhinagar, IISER, Thiruvananthapuram, and the International Centre for Theoretical Sciences, Bangalore, also played key roles in the data analysis.

The multiple efforts across the consortium converged on the same results – the signal had emerged from (the merger of two black holes) a distant part of the universe, perhaps a galaxy.

Physicists are celebrating the discovery for multiple reasons.

“This is an example of big science supported by big engineering,” said Dibyendu Nandi, a physicist at IISER, Calcutta, and head of the Centre for Excellence in Space Sciences, India, a facility supported by the Union human resources development ministry.

The Ligo detectors are marvels of engineering precision, designed to detect ripples or displacements in space billionths of the width of an atom using laser beams that are bounced off mirrors after travelling along two arms of the instrument, each 4km long.

“Gravitational waves was the one prediction of Einstein’s general relativity theory that had not been directly detected – until now,” said Nayak. “This discovery is important for another reason – it will open a new branch of astronomy, we can observe and study things we have never seen or observed before.”

Some physicists also point out that the signal represents the first direct evidence of black holes merging.

“There is no other way we could have detected such exotic events,” said Nandi, who is not associated with the search for gravitational waves. “This observation tells us that such events are not just theorists’ dreams, that the universe is as exotic as we have imagined it to be.”

source: http://www.telegraphindia.com / The Telegraph,Calcutta,India / Front Page> Story / by G.S. Mudur / Friday – February 12th, 2016