Gravitational Waves – No. 2

Back in February a major milestone in experimental physics was achieved: the direct discovery of gravitational waves. The LIGO team reported that these waves emanated from two ‘black holes’ merging together. Indeed it inspired me to write a post on the topic.

Today after all these months another gravitational wave event has been reported by LIGO! The relevant paper is here.

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Visualisation of black holes merging to produce gravitational waves (Source: T. Pyle/LIGO)

The event was recorded on December 26, 2015 at 03:38:53 UTC and lasted 1 second in the LIGO frequency band.

The gravitational wave signal from this event was weaker than that reported in February. But it has been deduced that in this event the black holes were about 3 times lighter and located around the same distance away (though there is a large uncertainty associated with the estimated distance). The masses deduced are still higher than that of a stable neutron star so it was concluded that the objects are black holes. New in this discovery is that the signal is strong enough to conclude that at least one of the black holes has spin i.e. it is rotating around its central axis. But the signal is not strong enough to deduce if the black holes are precessing i.e. if the axis itself is rotating relative to the orbital plane.

Several assumptions go into the reporting of such a result. For example, the inference of distance to the black holes assumes the ΛCDM cosmological model of the universe, which itself has been deduced from other astronomical observations. But once again Einstein’s general theory of relativity has stood the test of experiment and shown how to interpret the feeblest of our perceptions. The waveform predicted by relativity matches that observed. This complements the coincidental detection of the wave by LIGO’s two interferometers located in separate states in the USA.

In line with these observations, we should expect that events like these will be reported on a regular basis. The Analog world of general relativity has made a comeback, a new field of research is now Open.

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2 Responses to Gravitational Waves – No. 2

  1. Maggie says:

    Fascinating… I cannot pretend to understand it all, but I love to read about the universe and beyond…

  2. helloparth says:

    To help you understand it Maggie: imagine you look up at night and you see two stars coming together ,attracted by the ‘force’ of gravity, and eventually merging together into one star. But as they came together they released some of their energy in the form of ‘gravitational waves’. Just like water ripples in a pond except instead of water the medium is space and time itself. These waves have travelled all the way from the stars to Earth,at the same speed as their light travels, and have jiggled some mirrors in an experiment (called LIGO) very slightly but enough for the experimentalists to say they’ve discovered the waves. It’s fascinating to me too!

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