Ana Sayfa Physic Astrophysics New Model Improves Understanding of Gravitational Waves from Colliding Black Holes

New Model Improves Understanding of Gravitational Waves from Colliding Black Holes

New Model Improves Understanding of Gravitational Waves from Colliding Black Holes
New Model Improves Understanding of Gravitational Waves from Colliding Black Holes

New Model Improves Understanding of Gravitational Waves from Colliding Black Holes


The gravitational wave strain emitted by a perturbed black hole (BH) ringing down is typically modeled analytically using first-order BH perturbation theory. In this Letter, we show that second-order effects are necessary for modeling ringdowns from BH merger simulations. Focusing on the strain’s (ℓ,m)=(4,4) angular harmonic, we show the presence of a quadratic effect across a range of binary BH mass ratios that agrees with theoretical expectations. We find that the quadratic (4,4) mode’s amplitude exhibits quadratic scaling with the fundamental (2,2) mode—its parent mode. The nonlinear mode’s amplitude is comparable to or even larger than that of the linear (4,4) mode. Therefore, correctly modeling the ringdown of higher harmonics—improving mode mismatches by up to 2 orders of magnitude—requires the inclusion of nonlinear effects.

The paper discusses the use of innovative techniques to analyze the waves produced by black hole collisions. In 2015, scientists made the first-ever discovery of gravitational waves, which are space-time ripples resulting from major cosmic events such as the merging of black holes. The detection of these waves confirmed Einstein’s general theory of relativity, which proposed the existence of such waves if space-time functioned as he believed.

Over the past seven years, researchers have detected almost 100 merging black holes by monitoring the gravitational waves that these events emit. With the help of new research, modeling these cosmic events has become more complex. A team of 14 researchers led by Keefe Mitman, Macarena Lagos, Lam Hui, and Leo Stein developed an improved model that allows for a deeper understanding of the merging of black holes’ structure.

The team’s paper, “Nonlinearities in Black Hole Ringdowns,” published in Physical Review Letters, describes a more intricate way to model the signal emitted by gravitational waves, incorporating nonlinear interactions in the models.

This modeling approach will enable scientists to gain a better understanding of what is happening inside black holes and test whether Einstein’s general relativity accurately describes the behavior of gravity in extreme astrophysical environments.

Co-author Lagos believes that the research is a significant step towards advancing our understanding of gravity and cosmic phenomena happening in remote areas of the universe. The timing of this research is favorable because the LIGO observatory, which initially detected gravitational waves, will be activated in March 2023 after being closed due to the pandemic. With several other major detectors expected to start collecting data in the coming years, it is crucial to have advanced models to interpret incoming information accurately.

Co-author Lam Hui used an analogy to explain how gravitational waves can provide information about the inner contents of a black hole by listening to the sound emitted when it’s shaken. The “shaking” of black holes refers to the disruption that occurs when two black holes merge, and by listening to the harmonics it emits, scientists can assess the space-time structure of the black hole.

Previous models of gravitational waves after two black holes merge included only linear interactions, which provided valuable insights into black holes’ structure and contents. The new model developed by the researchers includes nonlinear interactions and could provide a 10% improvement in the overall accuracy of black hole models.

The authors of the paper explained the significance of using nonlinear models to describe gravitational waves by comparing them to ocean waves. If a wave rises and falls without spouting water, it can be described with a linear equation. However, a wave that crests and breaks exhibits nonlinear interactions where water swells at the wave’s bottom, while other water crashes in various directions, creating droplets of water. A nonlinear model would allow for a better understanding of how all the water, including the airborne droplets, moves within the wave.

Similarly, gravitational waves can be compared to water waves, and the new nonlinear model accounts for the extraterrestrial equivalent of airborne droplets. According to Leo Stein, one of the paper’s authors, the researchers are preparing themselves to be gravitational wave detectives who dig deeper to understand the nature of these waves.

Reference: “Nonlinearities in Black Hole Ringdowns” by Keefe Mitman, Macarena Lagos, Leo C. Stein, Sizheng Ma, Lam Hui, Yanbei Chen, Nils Deppe, François Hébert, Lawrence E. Kidder, Jordan Moxon, Mark A. Scheel, Saul A. Teukolsky, William Throwe and Nils L. Vu, 22 February 2023, Physical Review Letters.
DOI: 10.1103/PhysRevLett.130.081402


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