A hundred years after Albert Einstein’s prediction, gravitational waves from a binary black hole merger were detected by two US-based Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in September last year. But that was no fluke, as scientists Wednesday announced that the phenomenon was spotted a second time on December 26 last year.
The LIGO team officially announced the results at a media conference in the US.
LIGO research is carried out by the LIGO Scientific Collaboration (LSC), a group of more than 1,000 scientists from universities around the United States and in 14 other countries, including India.
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On December 26, 2015, the LIGO detectors at Hanford in Washington and at Livingston in Louisiana detected a signal from the coalescence of two black holes, with masses 14 and eight times the mass of Sun. They merged into a single, more massive, rapidly rotating black hole that is about 21 times the mass of Sun.
The event took place 1.4 billion years ago, lasted in LIGO’s frequency band for about a second, and released about 1 solar mass worth of energy in that short period. For comparison, only a tiny fraction of the Sun’s mass gets converted to light in its entire lifetime, which is enough to keep the earth warm for billions of years, according to an official release issued by the LIGO scientists.
Compared to the first binary black hole merger event announced in February 2016, however, the present one is less massive — 65 solar mass versus 21 solar mass.
Researchers at the Inter University Centre for Astronomy and Astrophysics (IUCAA) here in Pune told The Indian Express that these findings show scientists are in the right path of sensitivity. Prof Tarun Souradeep, senior scientist at IUCAA and one of the nine key researchers, said detecting gravitational waves will also become routine if LIGO-India is in place.
Dr Somak Roychoudhury, director, IUCAA, said detection of another binary black hole merger, coming barely two months after the first one was detected, will put an end to scepticism in scientific circles. “Clearly, this vindicates our stand that black holes are the new tools in gravitational wave astronomy,” Roychoudhury said. “Despite the significance of the detection of gravitational waves in September last year, there have been endless conversations and discussions on social media that doubted even the existence of black holes.
“With a third LIGO-India detector to be set up soon, detection of another binary black hole merger puts an end to any more doubts.”
Unlike the first event, the signal in the second instance does not stand out of the noise like a short-duration burst. One needs to use sophisticated data analysis techniques — matched filtering —to find such signals.
Many scientists in IPR, IUCAA and RRCAT are currently engaged in building a third LIGO detector in India, LIGO-India, that will significantly help detection of such events and dramatically improve the accuracy in estimating the location of binaries in the sky.