In 2019, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and the Virgo detector in Italy detected signals from gravitational waves that pointed to an unusually massive black hole. These signals, believed to be the result of a collision between two black holes that occurred billions of years ago, were of particular interest due to the unique properties of the black hole they indicated.
The Detection of the Signal Named GW190521
The unique signal, dubbed GW190521, is thought to represent the precise moment these two black holes merged. Despite it lasting less than one-tenth of a second, scientists calculated that it originated approximately 17 billion light-years away – a time when the universe was roughly half its current age.
Finding Out About the Masses of Black Holes Involved
The two colliding black holes were of different sizes. The larger one had a mass equal to 85 times that of our sun, while the smaller one was equivalent to 66 solar masses. After their merger, they formed a new black hole with about 142 solar masses. The energy equivalent to eight solar masses was released in the form of gravitational waves, resulting in the strongest wave detected by scientists to date.
Understanding Solar Mass and its Significance
A solar mass, astronomically defined as the mass of the sun or precisely, 1.989 x 10^30 kilograms (equivalent to about 333,000 Earths), is a key unit of mass utilized by astronomers. It helps in estimating and comparing masses of different celestial bodies effectively.
An Unusually Massive Black Hole: Breaking Traditional Knowledge
Traditionally, it is believed that stars capable of producing black holes between 65 and 120 solar masses do not do so because they explode and disintegrate when they die, rather than collapsing into a black hole. In this context, the 85-solar-mass black hole detected falls into an “intermediate-mass” range which is unusual according to the conventional knowledge.
Possible Reasons for the Unconventional Black Hole Mass
In trying to explain this anomaly, researchers propose that this larger black hole was not the result of a single collapsing star, but possibly the product of a previous merger.
Understanding Black Holes
Black holes are points in space where matter is so densely compressed that a gravity field is created from which not even light can escape. The concept was first theorized by Albert Einstein in 1915 and John Archibald Wheeler, an American physicist, coined the term ‘black hole’ in the mid-1960s.
The Varied Categories of Black Holes
Generally, black holes observed till date fall into two categories: black holes ranging between a few solar masses to tens of solar masses, forming when massive stars die; and supermassive black holes with masses ranging from hundreds of thousands to billions times that of our sun.
An Insight into Gravitational Waves
Gravitational waves are invisible ripples in space-time created when a star explodes in a supernova, two big stars orbit each other, or two black holes merge. These waves can travel at the speed of light and alter space-time causing it to stretch in one direction and compress in the other.
The field of gravitational waves is relatively new; although Albert Einstein proposed their existence in his General Theory of Relativity over a century ago, the first wave wasn’t detected until 2015 by LIGO.