The basic physics of the binary black hole merger GW150914

Abstract

The first direct gravitational-wave detection was made bythe Advanced Laser Interferometer Gravitational Wave Observatoryon September 14, 2015. The GW150914 signal wasstrong enough to be apparent, without using any waveformmodel, in the filtered detector strain data. Here, featuresof the signal visible in the data are analyzed usingconcepts from Newtonian physics and general relativity, accessibleto anyone with a general physics background. Thesimple analysis presented here is consistent with the fullygeneral-relativistic analyses published elsewhere, in showingthat the signal was produced by the inspiral and subsequentmerger of two black holes. The black holes were eachof approximately 35Msun, still orbited each other as close as∼350 km apart and subsequently merged to form a singleblack hole. Similar reasoning, directly from the data, is usedto roughly estimate how far these black holes were fromthe Earth, and the energy that they radiated in gravitationalwaves.