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GW190521 Gravitational Wave

GW190521 Gravitational Wave

Context:

A collision between two black holes billions of years ago sent gravitational waves rippling through the universe. 

  • GW190521 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 in 2019.
  • The signal detected at LIGO and Virgo resembled “about four short wiggles” and lasted less than one-tenth of a second.

Gravitational waves:

  • These waves were proposed by Albert Einstein in his General Theory of Relativity. In 2015, however, the first gravitational wave was detected by LIGO. Since then, there have been a number of subsequent detections of gravitational waves.
  • These are invisible ripples form when a star explodes in a supernova when two big stars orbit each other; and when two black holes merge.
  • These waves travel at the speed of light and squeeze and stretch anything in their path.

Source of gravitational wave:

  • GW190521 had most likely been generated by a merger of two black holes. The signal represented the instant that the two merged. 
  • But these findings led to further questions. One of the two merging black holes falls in an “intermediate-mass” range.
  • Intermediate-mass is a misfit that cannot be explained by traditional knowledge of how black holes form.

New findings:

  • So far all the black holes observed belong to either of the two categories.
    • First category: It ranges between a few solar masses (one solar mass is the mass of our Sun) and tens of solar masses. These are thought to form when big stars die.
    • Second category: It is of supermassive black holes. These range from hundreds of thousands to billions of times that of our sun.
  • According to scientists, stars that could give birth to black holes between 65 and 120 solar masses do not do so. Stars in this range blow themselves apart when they die, without collapsing into a black hole.
  • But in the merger leading to the GW190521 signal, the larger black hole was of 85 solar masses known as the pair-instability mass gap. It is the first “intermediate-mass” black hole ever observed.
  • The two black holes merged to create a new black hole of about 142 solar masses. After merging energy equivalent to eight solar masses was released in the form of gravitational waves. It is the strongest ever wave detected by scientists so far.

Black Holes

  • It is a place in space where gravity pulls so much that even light can not get out.
  • The gravity is so strong because the matter has been squeezed into a tiny space. This can happen when a star is dying.
  • As no light can get out, they are invisible.
  • Space telescopes with special tools can help find black holes. 
  • Black holes can be big or small, like as small as just one atom or have mass up to 20 times more than the mass of the sun (stellar). 
  • Stellar black holes are made when the center of a very big star falls in upon itself or collapses. When this happens, it causes a supernova.

Source: Indian Express