Relativity Lite

66 | Relativity Lite On December 26, 2015, a second merger was detected from a pair of black holes 1.4 billion light-years away and which had about 14.2 and 7.5 times the mass of the Sun. The 2017 Nobel Prize in Physics was awarded to three key figures in the development and success of LIGO: Barry Barish, Kip Thorne, and Rainer Weiss. Figure 14. The signals of gravitational waves detected by the twin LIGO observatories at Livingston, Louisiana, and Hanford, Washington, from the merger of two black holes. The top signal at Hanford arrived 1/7000th of a second after the signal first reached Livingston, the middle plot, which shows that it traveled at the speed of light. The bottom plot compares data from both detectors, with the Hanford data shifted by that time interval and inverted to account for the different orientation of the detectors at the two sites. The signals, including the instruments’ ever-present noise, were compared against numerous simulated signals, based on the equations of general relativity, varying by mass and distance. The best fit was for a merger of two black holes—one about 29 times the mass of the Sun and the other about 36 solar masses—lying 1.3 billion light-years away. This comparison is shown in white. Time is plotted on the x-axis and strain on the y-axis. Strain represents the fractional amount by which distances are distorted—less than the width of a proton. Image credit: Caltech / MIT / LIGO Lab. * * “Gravitational Waves, as Einstein Predicted,” LIGO Laboratory, https://​www​.ligo​.caltech​.edu/​image/​ligo20160211a (ac- cessed May 7, 2020).