The merger of black holes is one of the few events in the universe that has enough energy to
Simulation of black hole collisions. Video: John Hopkins University
Gravitational waves are extremely small.Typically, physicists have studied the waves emitted by black hole mergers by simplifying general relativity: they have used versions of the equations that ignore the weak and almost imperceptible but important gravitational effects of the merger.
In a new study, scientists presented a "head-on"collision of black holes moving at the speed of light. Although such an impact is extremely unlikely, simulations of this situation show waves strong enough for scientists to detect nonlinearities or gravitational effects that are ignored in "simplistic" simulations.
General relativity is non-linear, meaning that gravitational waves themselves will also produce more gravitational waves.
Mark Ho-Yuk Cheung, physicist at Johns Hopkins University, lead researcher
The researchers also studied another, moreprobable situation: gradual merger of two black holes orbiting each other. In this situation, scientists also discovered signs of nonlinear propagation of gravitational waves.
Artistic illustration of the merging of two blackholes. The behavior of gravitational waves at the initial stage (when approaching) and after the merger can be described by linear equations, but the merging process itself reveals nonlinear effects. Image: Kip Thorne (top); B. P. Abbott et al. (bottom), American Physical Society
The findings indicate that black hole mergers cannot be studied using simplified linear equations and that existing models need to be adjusted.
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