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Second breakthrough for LIGO detectors
Jul 12, 2016

LIGO scientists working with gravitational wave detectors at Livingston, Louisiana, and Hanford, Washington, U.S., have announced witnessing the merging of a second black hole pair.

They infer this from the observation of a gravitational wave (GW151226) detected on December 26, 2015. Being a much weaker signal than the first, the detection of this merger required the use of sophisticated noise filtering and mathematical analyses, some of which has been developed by Indian scientists.

In detail:

  • The entire signal, coming from 1.4 billion light years away, lasted just one second. Having approximately 14 and 8 times the mass of the sun, the two black holes, during their cataclysmic merging, released approximately one solar mass within this short interval. They then merged to form a black hole of approximately 21 solar mass.
  • While LIGO’s first detection, reported on Feb. 11, produced a clear peak, or “chirp,” in the data, this second signal was far subtler, generating a shallower waveform that was almost buried in the data. Using advanced data analysis techniques, the team determined that indeed, the waveform signaled a gravitational wave. A special technique called matched filtering invented in 1949 by Wiener had to be adapted for gravitational wave data analysis.
  • The researchers calculated that the gravitational wave arose from the collision of two black holes, 14.2 and 7.5 times the mass of the sun. The signal picked up by LIGO’s detectors encompasses the final moments before the black holes merged. This cataclysm produced a more massive spinning black hole that is 20.8 times the mass of the sun.
  • This second detection of gravitational waves, which once again confirms Einstein’s theory of general relativity, successfully tested LIGO’s ability to detect incredibly subtle gravitational signals.

What is LIGO:

What are gravitational wavesLIGO Scientific Collaboration (LSC) is a group of scientists seeking to make the first direct detection of gravitational waves, use them to explore the fundamental physics of gravity, and develop the emerging field of gravitational wave science as a tool of astronomical discovery. The LSC works toward this goal through research on, and development of techniques for, gravitational wave detection; and the development, commissioning and exploitation of gravitational wave detectors. Founded in 1997, the LSC is currently made up of more than 1000 scientists from dozens of institutions and 15 countries worldwide.What are gravitational waves:

  • Gravitational waves are distortions or 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe.
  • Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity.

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