Experimental physicist key to the detection of gravitational waves.
2017 Nobel Prize in Physics
Comment & Review
The detection of gravitational waves is the culmination of many decades of persistent theoretical, observational and engineering work. While heralded as surprising, that the first detected wavescame from binary black holes was indeed theoretically expected.
A momentous signal from space has confirmed decades of theorizing on black holes — and launched a new era of gravitational-wave astronomy.
The announcement confirming the discovery of gravitational waves created sensational media interest. But educational outreach and communication must remain high on the agenda if the general public is to understand such a landmark result.
Gravitational waves are predicted by general relativity, but their direct observation from astronomical sources hinges on large improvements in detection sensitivity. The authors review how squeezed light and other quantum optical concepts are being applied in the development of next generation interferometric detectors.
The Laser Interferometer Gravitational Wave Observatory in the USA is searching for gravitational-wave emissions from cataclysmic astrophysical events. The task has required the construction of the world's largest and most sensitive optical strain sensor.
Observables & Implications
The general theory of relativity predicts that all accelerating objects produce gravitational waves — analogous to electromagnetic waves — that should be detectable for instance in the case of extremely massive objects such as black holes undergoing acceleration. The existence of such waves has been inferred indirectly, but an important goal in physics is their direct observation, a feat that would both validate Einstein's theory and lead to new areas of cosmology. Now early results from LIGO (the Laser Interferometer Gravitational-Wave Observatory), one of the handful of detectors searching for gravity waves, have provided a starting point for further gravity hunts by deriving an upper limit for the stochastic background of gravitational waves of cosmological origin. The data rule out models of early Universe evolution with a relatively large equation-of-state parameter, as well as cosmic (super)string models with relatively small string tension that are favoured in some string theory models.
Advanced LIGO has detected gravitational waves from two binary black hole mergers, plus a merger candidate. Here the authors use the COMPAS code to show that all three events can be explained by a single evolutionary channel via a common envelope phase, and characterize the progenitor metallicity and masses.
The spins of the black holes involved in each of the four mergers that have been detected in gravitational waves so far were either small or not aligned with the binary orbit.
The first gravitational-wave source from the isolated evolution of two stars in the 40–100 solar mass range
Numerical simulations of the formation of binary black holes provide a framework within which to interpret the recent detection of the first gravitational-wave source and to predict the properties of subsequent binary-black-hole gravitational-wave events; the calculations predict detections of about 1,000 black-hole mergers per year once gravitational-wave observatories reach full sensitivity.
Squeezed states of light have been experimentally demonstrated to improve the performance of the Laser Interferometer Gravitational-wave Observatory (LIGO) in astrophysically relevant frequency regions. This enhanced performance may help to reach the sensitivity required for detecting gravitational waves.
Researchers demonstrate a laser interferometer that achieves simultaneous nonclassical readout of two conjugated observables. Because their system uses steady-state entanglement, it does not require any conditioning or post-selection. By distinguishing between scientific and parasitic signals, its sensitivity exceeds the standard quantum limit by about 6 dB.
Quantum metrology employs the properties of quantum states to further enhance the accuracy of some of the most precise measurement schemes to date. Here, a method for estimating the upper bounds to achievable precision in quantum-enhanced metrology protocols in the presence of decoherence is presented.
‘Squeezed light’ enables quantum noise in one aspect of light to be reduced by increasing the noise, or more accurately the quantum uncertainty, of a complementary aspect. This has now been used to push the detectors at the heart of the GEO600 gravitational wave observatory to unprecedented levels of sensitivity.
Substantial improvements, through the use of squeezed light, in the sensitivity of a prototype gravitational-wave detector built with quasi-free suspended optics represents the next step in moving such devices out of the lab and into orbit.
On astronomical scales, gravity is the engine of the Universe. The launch of LISA Pathfinder this year to prepare the technology to detect gravitational waves will help us 'listen' to the whole Universe.
Strong evidence that a kilonova — an event similar to a faint, short-lived supernova — accompanied the short-duration γ-ray burst GRB 130603B provides support for the hypothesis that such bursts are produced by the merger of two compact stellar objects.
The first detection of electromagnetic emission from a gravitational wave source bridges the gap between one of the most energetic phenomena in the Universe and their dark, difficult to detect progenitors.