Astronomers hunt gravitational waves with ear to black hole symphony

Once detected, such low frequency gravitational waves would provide scientists with a novel look of the universe

Indian astronomers have released their first set of data that will be vital for an international collaboration to detect extremely weak gravitational waves by listening to the “symphony of black holes in the universe.”

Once detected, such low-frequency gravitational waves would provide scientists with a novel look at the universe from a completely new window that was opened in 2015 with the discovery of the first gravitational wave.

gravitational waves are extremely feeble ripples in spacetime caused by massive objects like black holes. But they are so elusive that it took scientists decades to capture them using an instrument built after spending nearly a billion dollars. Some of the key scientists associated with the breakthrough were awarded the Nobel Prize within two years.

But that was one half of the story. All the gravitational wave signatures picked up so far are high-frequency waves as identifying the low-frequency ones is even more complicated. This is what an international collaboration spread over four continents seeks to achieve.

“It is akin to watching a star in the X-ray spectrum, but not in the visible range. For a holistic view we need to see the star from both sides of the electromagnetic band,” lead researcher from India Bhal Chandra Joshi from TIFR’s National Centre of Radio Astronomy, Pune told DH, explaining why gravitational waves need to be seen from both sides.

For more than a decade Joshi and his team members observed pulsars using the upgraded Giant Metrewave Radio Telescope (uGMRT) at Khodad near Pune.

The pulsars are rotating neutron stars that are known to emit beams of electromagnetic radiation from their poles with such precise intervals that they are considered better than atomic clocks. They are known as nature’s best timekeepers.

But there are fine delays in the arrival times of radio pulses from one particular group of pulsars (millisecond pulsar), which Indian scientists captured in the last three and half years. The data would help filter signals from background noise while identifying low-frequency gravitational waves.

“The interplay of gravitational waves in the universe is similar to a symphony being played by nature. But the symphony has a hiss underneath making the lower notes inaudible. We must filter these distracting sounds to enjoy the true symphony,” the scientists from Indian Pulsar Timing Array said in a statement.

The InPTA is a part of an Asian consortium involving Indian and Japanese scientists. There are three similar consortia working in Australia, North America and Europe. All four groups periodically share their results in the global hunt to look for the signatures of long-sought but evasive low-frequency gravitational waves.

“With millisecond pulsars as our probes, we measure the noise so that together with the other scientific groups, we can listen to the symphony of black holes in the universe,” said Joshi. “It would complete the history of the universe.”