A new cosmic model to reveal what’s inside colliding black holes

An artist’s impression of two black holes about to collide and merge. New research has led to the development of a more sophisticated model for modeling cosmic events, which will allow for a deeper understanding of the structure of merging black holes.

A research paper uses new methods to analyze the waves that black holes emit when they collide.

In 2015, scientists for the first time detected gravitational waves, ripples in space-time that occur when large cosmic events – such as the collision and merger of two black holes – disrupt the cosmos. The observation of these waves confirmed Einstein’s theory of general relativity, which predicted that such waves would occur if space-time worked as he believed it did. In the seven years since, nearly 100 merging black holes have been discovered by observing[{” attribute=””>gravitational waves that these extraterrestrial events emit.

Now, thanks to new research, the ability to model these cosmic events has become more sophisticated. The team of 14 researchers was led by Caltech PhD student and Columbia College alum Keefe Mitman (CC’19), Columbia postdoc Macarena Lagos, Columbia Professor Lam Hui, and University of Mississippi professor Leo Stein. The improved model that they developed paves the way for a deeper understanding of the structure of merging black holes.

In “Nonlinearities in Black Hole Ringdowns,” a new paper published in Physical Review Letters, the team outlines a more complex way to model the signal that gravitational waves emit by including nonlinear interactions in the models. This modeling method will allow scientists to better understand the structure of what’s happening inside of black holes, and will also help test whether Einstein’s theory of general relativity correctly describes the behavior of gravity in extreme astrophysical environments.

A computer rendering of two black holes that are about to merge, as viewed from above. Credit: SXS Lensing/Simulating eXtreme Spacetimes Collaboration

“This is a big step in preparing us for the next phase of gravitational wave detection, which will deepen our understanding of gravity and these incredible phenomena taking place in the far reaches of the cosmos,” Lagos, a co-author on the paper, said.

The research comes at an opportune time: This March,

To understand the importance of using nonlinearity to describe gravitational waves, the authors described waves in an ocean: A wave that rises and falls without spouting water into the air could be described with a linear equation. But a wave that crests and breaks exhibits nonlinear interactions: While some water swells at the wave’s bottom, other water is simultaneously crashing left, right, up, and down in tendrils and droplets of water above it. A nonlinear model of the wave would allow you to understand how and when all of the water in the wave, including those airborne droplets, is moving. Gravitational waves are similar to water waves, and the new model is able to account for the extraterrestrial equivalent of extra water droplets.

“We’re getting ourselves ready for when we’re going to be gravitational wave detectives, when we’ll be digging deeper to understand everything we can about their nature,” Stein, one of the paper’s authors, said.

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