LIGO's Gravitational Wave Discovery is the Physics World 2016 Breakthrough of the Year

Nicholas Lockerbie

Physics World, the UK’s Institute of Physics magazine, announced recently that LIGO’s gravitational wave discovery is the Physics World 2016 Breakthrough of the Year—nine other achievements being highly commended.  The direct detection of gravitational waves by the two LIGO (Laser Interferometer Gravitational wave Observatory) detectors in the USA, announced on 11 February of this year, was actually the culmination of decades of scientific and technological effort by the LIGO Scientific Collaboration (LSC)—an international organisation which numbers some 1000 scientists and engineers in its ranks.

The source of the detected gravitational waves turned out to be a revelation: they came from the inspiral and merger of two Black Holes, around 1.3 billion light years away. The resulting gravitational ‘chirp,’ which was detected at both LIGO sites, lasted for just 0.2 seconds.  Even so, it provided sufficient detailed information for the LSC’s astrophysicists to determine that the Black Holes had an initial combined mass of approximately 65 M_€ (where M_€ is the mass of the Sun); and, on further investigation, they discovered that the luminosity of the event briefly outshone—in terms of its emitted (gravitational wave) power—and by a factor of 50, the electromagnetic output of all the stars in the observable Universe, combined.  A truly cataclysmic event! Furthermore, a short 103 days after the first detection (which actually took place on 14 September, 2015) a second detection was made by LIGO, with the gravitational waves coming once more from a pair of colliding Black Holes. This time, their combined initial mass was ‘just’ 22 M_€, but the LSC’s scientists were able to follow their inspiral and merger for a full second. Astonishingly, these Black Holes were found to have been orbiting each other 225 times per second—just prior to their merger into a single Black Hole.

Professor Nicholas Lockerbie led the LSC work which was carried out here in the Department of Physics, this work being focused, in part, on the design and construction of specialised low-noise electrostatic actuators for LIGO. Eight of these remotely-controllable bespoke instruments were supplied to LIGO as a part of the ‘advanced’ upgrade to the sensitivity of LIGO’s interferometric detectors. In fact, the actuators were used at the ‘sharp end’ of the eventual gravitational wave detection—for the contactless steering of the detectors’ test-masses / mirrors.

Professor Lockerbie said: “I hope that the worldwide acclaim which this work continues to receive will provide a stimulus to the long-term funding of bold high-risk / high-reward physics projects in the future.”

December 2016