In a first, a team of astronomers has detected gravitational waves emerging from the merger of two Binary Black Holes (BBH) with significantly unequal masses.
Named GW190412, the merger was collectively detected on April 19, last year. The highly-sensitive signals were detected using Laser Interferometer Gravitational wave Observatory (LIGO) and Virgo, located in the US and Italy, respectively.
It was 2015 when gravitational waves were first detected on Earth and since then, observatories have been scanning the skies for more traces in the form of some signals.
However all discoveries of BBH mergers, by far, were those involving black holes of comparable or near equal masses, making this detection a rare event.
Couple of weeks after these detectors were up and functioning for the third operational cycle in April 2019, they picked up gravitational waves emerging from this merged BBH, believed to be located some 2.3 billion light years away from earth.
While one of the components weighed 30 solar mass, the other was nearly 3.6 times lighter, and weighed just about 8 solar mass. The duo is said to be unique in the manner that they merged, confirming that astrophysical BBH comprises systems with unequal masses, knowledge of which was only limited to theories till date.
Moreover, the difference in masses of the two BBH union sent out gravitational waves with subtle variations in the form of higher ‘harmonics’ in the waveform.
“These variations, which appear as higher ‘harmonics’ in the waveform, have been observed for the first time in this event,” read the official statement issued by Caltech on Monday.
What this essentially means is that, the mass difference produces specific signal modulations, as predicted by theory.
“In fact, the mass imbalance produces an unusually high intensity of gravitational radiation in the so-called ‘Higher Order Modes’, which were detectable in GW190412 and provide yet another confirmation of the validity of Einstein’s General Relativity,” read the statement released by Virgo on Monday.
The possibility of more such mergers involving unequal BBHs in future cannot be ruled out, said Somak Raychaudhury, director of the Inter University Centre for Astronomy and Astrophysics (IUCAA), which is one of the Indian institutes involved in gravitational wave research representing the Indian consortium of LIGO.
“It is under extremely complicated scenarios that BBH mergers occur. These mergers could be a result of several possibilities. Since we have, so far, detected mergers of equal mass BBHs, it looks like those of unequal masses are more rarer. But, we will need more number of detections to comment authoritatively.”
Theoretically, such variations in signal were expected and the gravitational wave scientists had ensured to keep the detectors fine-tuned to discover these signals early on, Tarun Souradeep, senior physicist and LIGO India spokesperson, told The Indian Express.
“As we detect more such mergers with rare BBHs combinations, we may stumble upon fast spinning ones, which have not been seen so far,” said Souradeep.
The operations of LIGO and Virgo were suspended on March 26, following the outbreak of COVID-19. As per the original schedule, the cycle was scheduled till the end of April, before shutting down temporarily for an upgrade planned over the next one year.