Context: Billions of years ago, collision between two black holes sent gravitational waves rippling through the universe.In 2019,signals from these waves were detected at the gravitational wave observatory LIGO (United States) and the detector Virgo(Italy).

• These waves were a result of a collision between two black holes billions of years ago.

Key Points

• The signal has been named GW190521 and likely represented the instant that the two black holes merged.
• It lasted less than one-tenth of a second.
• It was calculated to have come from roughly 17 billion light-years away, a time when the universe was about half its age.
• Out of the two, the larger black hole was of 85 solar masses and the smaller black hole was of 66 solar masses. Post-merger they created a new black hole of about 142 solar masses and energy equivalent to 8 solar masses was released in the form of gravitational waves, leading to the strongest ever wave detected by scientists so far.
• A solar mass is the mass of the sun or more precisely, it is 1.989 x 1030 kilograms, which is equivalent to about 333,000 Earths.
• Astronomers use a solar mass as a basic unit of mass.

Unusual Mass Category

• The black hole with 85 solar masses falls in an “intermediate-mass” range (first-ever to be observed) and it defies the traditional knowledge of how black holes are formed.
• According to traditional knowledge, stars that could give birth to black holes between 65 and 120 solar masses do not do so because they blow themselves apart when they die, without collapsing into a black hole.
• In the merger leading to the GW190521 signal, the larger black hole was well within the unexpected range, known as the pair-instability mass gap.

Suggested Reasons for Unusual Mass

• The researchers suggest that the larger 85-solar-mass black hole was not the product of a collapsing star but was itself the result of a previous merger.

Key Facts

• GW190521: It is a gravitational wave signal resulting from the merger of two black holes near a third supermassive black hole.The event was observed by the LIGO and Virgo detectors on 21st May,2019.
• Researchers say that the single entity produced from the colliding of two black holes has a mass 142 times that of our Sun.

Additional Facts:

• Gravitational waves: These are ‘ripples’ in space-time caused by some of the most violent and energetic processes in the Universe.They are formed when a star explodes in a supernova; when two big stars orbit each other; and when two black holes merge.
• Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity.In 2015, the first gravitational wave was detected by LIGO.
• Black Hole: It is a region of space where matter has collapsed in on itself.The gravitational pull is so strong that nothing not even light can escape
• Black holes emerge from the explosive demise of certain large stars.But some are truly gargantuan and are billions of times the mass of our Sun.They are detected from the way they influence their surroundings.They produce observable gravitational waves as they spiral into each other.

Laser Interferometer Gravitational-Wave Observatory(LIGO): It is a large-scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool.

• Locations: Hanford Site, Washington(US) and Livingston, Louisiana(US).
• Virgo interferometer: It is a large interferometer designed to detect gravitational waves.It is a part of a scientific collaboration of laboratories from six countries: Italy and France, the Netherlands, Poland, Hungary and Spain.
• Location:Santo Stefano a Macerata, near the city of Pisa, Italy.