Introduction
As per the media reports in April 26, 2020, the gravitational wave observatories at Laser Interferometer Gravitational-wave Observatory (LIGO) for that first time detected merger of two unequal-mass black holes. This finding was published in preprint server ArXiv. The event was also confirmed by researchers from the International Centre for Theoretical Sciences (ICTS), a centre of the Tata Institute of Fundamental Research (TIFR), Bengaluru.
Salient Features of the Event
Some of the salient features of the event are as follows:
(i) The merger was observed on April 12, 2019, and was dubbed GW190412. It occurred almost five years after the first ever detection of gravitational wave signals, dubbed GW150914, was made by the LIGO observatories on September 14, 2015.
(ii) The event involved the merger of two black holes of unequal masses, i.e., 8 and 30 solar masses, or 8 and 30 times the mass of the sun. The actual merger took place at a distance of 2.5 billion light years away. A solar mass is the mass of the sun equal to approximately 2×1030 kg, a standard unit of mass in astronomy. A light year is a unit of astronomical distance, light takes to travel in a year, which is approximately 9.4607 ×1012 km or nearly to million miles.
(iii) It is a unique discovery because it involves the merger of two unequal masses of the blackholes. Because all binaries observed previously by the LIGO and Virgo (Italy) detectors were based on two roughly similar masses. It will make it easie to infer a more accurate determination of the distance from the event; the spin or angular momentum of the black hole with more mass; and the orientation of the whole event with respect to viewers on the Earth.
(iv) While the mass of the black hole bends the space-time close to it, the spin or angular momentum of this inscrutable object drags the nearly space-time, causing it to swirl along with it.
(v) The difference between binary black holes of equal and unequal masses is that of the emission of gravitational waves dominant emission of gravitational waves happens at twice the orbital frequency of the binary. In this event, the emission at a frequency that is three times the orbital frequency, are observed whereas this emission is negligible in case of binaries with equal masses.
(vi) When the merger of unequal black holes takes place, the spin of the more massive black hole can be determined from the extra features in the signal waveform. As the spin of the heavier black hole plays a more prominent role in the dynamics of the binary, it has a stronger impact on the waveform, which makes it easy to measure.
(vii) This event, confirms to the theory of general relativity published by Albert Einstein in 1915. The first direct detection of gravitational waves and the first observation of the collision and merger of a pair of black holes are key predictions of the theory.
What is a Black Hole?
A black hole is a place in space where gravity pulls so much that even light cannot escape it, because matter is squeezed into a tiny space. They are invisible and can be detected only with the help of space telescopes with special tools. Scientists are of the view that black holes are of different sizes, from the smallest as just one atom to the largest with a mass equal to about 4 million suns, like the supermassive black hole at the centre of the Milky way galaxy, called Sagi Harius A. Gravitational waves are created when two black holes orbit each other and merge.
There is a boundary at the edge of a black hole, called the event horizon, which is the point of no return. Whatever crosses it is sucked into the black hole, and is squished into a single point with infinite density, called the singularity. To escape from getting sucked, a thing has to travel faster than the speed of light, which is impossible.
About LIGO
Laser Interferometer Gravitational-wave observatory (LIGO) is the world’s largest gravitational wave observatory. It comprises two widely separated interferometers within the United States—one in Hanford, Washington, and another in Livingston, Louisiana. They work in unison to detect gravitational waves. The organisation chiefly aims to detect gravitational waves, the data may affect many areas of physics like gravitation, relativity, astrophysics, nuclear physics, etc.