![]() ![]() ![]() LIGO is the world's largest gravitational wave observatory and one of the world's most sophisticated physics experiments. The direct observation of a binary black hole merger would therefore provide a powerful cosmic laboratory for testing Einstein's theory. the pattern of gravitational waves emitted by the black holes as they approach ever closer and finally merge into a single, larger black hole - in accordance with the predictions of general relativity. These computer models have allowed us to construct precise gravitational waveforms - i.e. There is also evidence of many black hole candidates with much lower masses (ranging from a few, to a few dozen, times the Sun's mass), believed to be the remnants of dead stars that have undergone a cataclysmic explosion known as a core-collapse supernova.Īlongside this substantial progress in the indirect observation of black holes, there have been dramatic improvements in our theoretical understanding of these bizarre objects - including, over the past decade, some remarkable advances in modeling a pair of black holes (referred to as a binary) through several close orbits before they finally merge. For example, it is thought that most galaxies in the Universe, including the Milky Way, contain a supermassive black hole at their center - with masses millions or even billions of times that of the Sun. Although by definition we cannot directly "see" light from a black hole, astronomers have gathered a great deal of circumstantial evidence for their existence by studying the effects of black hole candidates on their immediate surroundings. In the same year that Einstein predicted gravitational waves, the physicist Karl Schwarzschild showed that Einstein's work permitted the existence of black holes: bizarre objects which are so dense and so compact that not even light can escape their gravitational field. Nevertheless the direct detection of gravitational waves as they reach the Earth has been hugely anticipated by the scientific community as this breakthrough would provide new and more stringent ways to test general relativity under the most extreme conditions and open up an entirely novel way to explore the Universe. The results of these indirect studies agree extremely well with Einstein's theory - with their orbits shrinking, exactly as predicted, due to the emission of gravitational wave energy. Over the past few decades astronomers have amassed strong supporting evidence that gravitational waves exist, chiefly by studying their effect on the motions of tightly orbiting pairs of stars in our Galaxy. These ripples travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself. Their existence was predicted by Einstein in 1916, when he showed that accelerating massive objects would shake space-time so much that waves of distorted space would radiate from the source. Gravitational waves are "ripples" in space-time produced by some of the most violent events in the cosmos, such as the collisions and mergers of massive compact stars. This remarkable discovery marks the beginning of an exciting new era of astronomy as we open an entirely new, gravitational-wave, window on the Universe. LIGO estimated that the peak gravitational-wave power radiated during the final moments of the black hole merger was more than ten times greater than the combined light power from all the stars and galaxies in the observable Universe. It was observed on Septemby the two detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO), arguably the most sensitive scientific instruments ever constructed. This cataclysmic event, producing the gravitational-wave signal GW150914, took place in a distant galaxy more than one billion light years from the Earth. We report on two major scientific breakthroughs involving key predictions of Einstein's theory: the first direct detection of gravitational waves and the first observation of the collision and merger of a pair of black holes. Observation of Gravitational Waves from a binary black hole mergerĪlbert Einstein's general theory of relativity, first published a century ago, was described by physicist Max Born as 'the greatest feat of human thinking about nature'. ![]()
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