# Gravity Research at BYU

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### Black Holes & Gravitational Waves

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### Dendro-GR

### Chaos in Relativity

### Neutron Stars

### Relativistic Fluid Dynamics

### LISA

### Gravitational Waves

Changes in a gravitational field propagate as gravitational radiation. The merger of two compact objects—black holes or neutron stars—results in the release of a phenomenal amount of energy in gravitational waves. These waves have recently been detected by two observatories, LIGO in the United States and Virgo in Italy. We use large supercomputers to study merging binaries and to predict the spectrum of their emitted gravitational waves.

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### Binary Black Holes

Binary black holes are the strongest astrophysical sources of gravitational waves. LIGO has observed black holes with masses 10—100 times the mass of the sun, moving at half the speed of light in orbits less than 100 km in radius. These dynamic and strong gravitational systems allow us to test general relativity in new ways, and to learn more about the population of black holes in our universe.
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### Neutron Stars

When some stars exhaust their nuclear fuel, the core can collapse, blowing off the outer layers of the star, resulting in a small dense neutron star with a radius of only about 10—12 km. The merger of two neutron stars can result in neutron-rich ejecta, that powers the formation of new elements. While we know that supernova create many of the elements heavier than helium, it now appears that merging neutron stars are primarily responsible for the elements heavier than iron.
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### Gravitational Chaos

The three-body problem in Newtonian gravity can have deterministic chaos. We use the post-Newtonian approximation to investigate chaos in multi-body problems in general relativity. These chaotic interactions may lead to the formation of potential gravitational wave sources in dense stellar clusters.
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### Dendro-GR

Dendro-GR is an open-source project for relativistic astrophysics. Based on the original Dendro project, Dendro-GR includes extensions for solving the Einstein equations in different formulations.
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### Beyond General Relativity

While general relativity matches all of the observational evidence that we have so far, our understanding of gravity is incomplete. Binary mergers, among the most dynamic and energetic gravitational events, might provide some clues for improving our understanding of gravity. We can compare observations of gravitational waveforms not only with the predictions of general relativity, but also those from other gravitation models. We are exploring changes to general motivated by string theory and other ideas in modern physics.
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### Relativistic Fluid Dynamics

Relativistic fluids are used to model everything from diffuse accretion disks, to the incredibly dense centers of neutron stars, to the relativistic jets emerging around black holes. Modeling such a large range of densities and velocities is very demanding and requires very robust numerical methods. We use high-resolution shock-capturing methods for relativistic CFD.
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### Wavelet Adaptive Multi-Resolution

Simulations of binary mergers are difficult to perform, usually requiring long and expensive runs on large supercomputers. New techniques are needed so that we can perform longer and more accurate simulations. Wavelet expansions can be used to generate sparse, efficient computational grids that naturally conform to features of the solution. We are developing wavelet-based multi-resolution and other techniques to help accelerate gravitational wave science.
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