First detection of gravitational waves: GW150914

Scientists detect gravitational wave signal from the merging of two black holes.

At 09:51 GMT on 14 September 2015, the two Laser Interferometer Gravitational Wave Observatory (LIGO) detectors picked up the first ever direct signature of gravitational waves.

The signal was named GW150914 from 'Gravitational Wave' and the date of observation.

Gravitational waves

Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained.

They are ripples in the fabric of spacetime originating from a cataclysmic event in the distant universe. Their detection confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes.

Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes. This merger produces a single, more massive, spinning black hole, converting a portion of the combined black holes’ mass to energy following Einstein’s famous formula E=mc2. This energy is emitted as a final, strong burst of gravitational waves.

Collisions of two black holes in this way had been predicted but never observed.

Working with LIGO

The LIGO group is made up of more than 1000 scientists worldwide who have joined together in the search for gravitational waves.

The search for events in the LIGO data requires sophisticated search algorithms and considerable computing power. Our scientists played a key role in the development of the algorthims that search for the merging of compact objects, particularly black hole binaries.

Thanks to funding from the Science and Technology Facilities Council, we also provide some of the computational resources used in the ongoing searches.

Our researchers have developed detailed models of the merging of black holes, using detailed numerical relativity simulations of Einstein's theory of General Relativity. Using these models, the LIGO team estimates that the black holes for this event were about 29 and 36 times the mass of the sun. Energy equivalent to around 3 times the mass of the sun was converted into gravitational waves in a fraction of a second, with a peak power output greater than all the stars in the observable Universe. It is these gravitational waves that LIGO detected.

Other contributions to the detection of GW150914 include:

• our researchers played a leading role in the algorithms that search for compact binary coallescences, particularly binary black holes
• our numerical relativity models of binary black hole systems were used to find the properties of the black holes in GW150914
• we support the detector characterisation and operation of the LIGO detectors.

For data relating to GW150914, please see the LIGO Open Science Centre.