When two black holes come together, they cause ripples in space and time which are called gravitational waves. Before this, people who studied black hole merges used math to work out what happens in those situations but they assumed the waves did not interact with each other. But recent research has shown that the waves do interact and this changes how we think of them.
Keefe Mitman, a graduate student from Caltech along with Saul Teukolsky (former Caltech graduate), explored the ‘nonlinear effects’. This is when waves move and crash against each other rather than just coasting by themselves. They discovered that nonlinear effects are created during violent events such as black hole merges through observing models of them. With new methods for looking at the patterns of these models, they were able to locate these complicated movements.
Discovering Nonlinear Effects in Black Hole Collisions
Researchers from Caltech, Columbia University, the University of Mississippi, Cornell University, and the Max Planck Institute for Gravitational Physics made a new discovery. It was published in the journal Physical Review Letters.
Keefe Mitman, a graduate student at Caltech, made a mathematical model of black hole collisions that has nonlinear gravitational effects. He compared this to what happens when two people jump together on a trampoline!
In the future, scientists are going to use a new model to discover more facts about how black hole collisions work. We can observe these collisions thanks to LIGO (Laser Interferometer Gravitational-wave Observatory). This year, LIGO will have some upgrades that make it even better at detecting gravity waves from space than before.
Mitman and some of his friends make up a research team called “Simulating eXtreme Spacetimes” (or SXS). This project was began by Teukolsky in partnership with Nobel Prize-winning scientist Kip Thorne who used to work at Caltech. The goal of SXS is to try and figure out how two black holes interact with each other as they spin around one another and eventually combine together. To do this, they rely on the equations created by Albert Einstein in his famous theory of relativity. Even more remarkable, it was Teukolsky that first figured out how to use these special equations to explain the moments after two supermassive objects hit each other (called the “ringdown” phase).
Supercomputers are needed to accurately figure out all the steps of two black holes spinning around each other and merging together into one. Years ago, Kip helped Dr. Teukolsky write his PhD thesis about this process which was based on a linear theory. Now, with a new nonlinear theory, it’s possible to get even more accurate predictions about how the black holes will act, so we can find out if general relativity is really true when it comes to describing the behavior of black holes.
SXS simulations have been very useful in figuring out the almost 100 black hole crashes that LIGO found. This new research is the first time ever to show nonlinear effects from simulations of the ringdown phase.
It’s like two people bouncing on a trampoline. If they bounce gently, it won’t affect each other at all – this is called linear theory. But if one person bounces with more energy then the trampoline starts to move around and the other person starts to feel that movement – this is what we call nonlinear. In other words, the two people start feeling each other’s presence due to the extra movements created by one of them.
Recently, some computer simulations made a special discovery. They found that when you look at the big waves of gravity, there is an extra wave hiding underneath with its own frequency! This helps scientists understand black hole collisions and test Albert Einstein’s theories about space even further.
Macarena Lagos, who co-authored the research, said that this big step will help us learn more about gravity when looking at special events taking place far away in outer space.
This passage is about a research paper called “Nonlinearities in Black Hole Ringdowns”, which was written by Keefe Mitman and co-authors on February 22nd, 2023. This paper talks about how black holes might behave differently than as predicted by current scientific theories. The paper’s details can be found online using its DOI (Digital Object Identifier) number: 10.1103/PhysRevLett.130.081402.
This study was supported financially by the Sherman Fairchild Foundation, National Science Foundation, Columbia University’s Innovative Theoretical Cosmology Fellowship, Department of Energy, and the Simons Foundation.
