“Quantifying Horizon Flux Effects on Binary Black Hole Dynamics”

arXiv:2408.15322v1 Announce Type: new
Abstract: Binary systems of black holes emit gravitational waves as they move through their orbits. While most of the emitted radiation escapes to future null infinity, a small fraction is absorbed by the black holes themselves. This is known as horizon absorption or tidal heating/torquing, and causes the black holes’ masses and spins to change as the system evolves. In this work, we quantify the effects of the horizon flux on binary black holes dynamics by computing them up to next-to-next-to-leading order on generic planar orbits, also exploring physically motivated factorizations of the results. We integrate these fluxes over unbound, hyperbolic-like trajectories obtained with the Effective-One-Body model TEOBResumS. We discuss the resulting phenomenology across a sizable slice of the relevant parameter space, finding a very small effect in most cases, except on highly energetic orbits. However, the predicted mass and spin variations are quantitatively and qualitatively very sensitive to the analytical representation chosen for the fluxes in that regime. We then perform comparisons with numerical relativity data of induced spins from hyperbolic encounters of initially nonrotating black holes, finding that the next-to-next-to-leading order factorized expressions we derive are crucial to reproduce the data. An optimization on the initial conditions (energy, angular momentum) is necessary for this, however, with differences of up to $9%$ between the numerical and optimal initial data. Finally, we use our analytical expressions to model possible astrophysical implications for black holes in globular clusters.

Abstract: Binary systems of black holes emit gravitational waves as they move through their orbits. In this work, we examine the effects of horizon flux on binary black hole dynamics, quantifying them up to next-to-next-to-leading order on generic planar orbits. We integrate these fluxes over unbound, hyperbolic-like trajectories obtained with the Effective-One-Body model TEOBResumS. We find that the effects of horizon flux are generally small, except on highly energetic orbits. However, the mass and spin variations are sensitive to the analytical representation chosen for the fluxes in that regime. We compare our predictions with numerical relativity data of induced spins from hyperbolic encounters of initially nonrotating black holes and find that the next-to-next-to-leading order factorized expressions are crucial to reproduce the data. We also highlight the importance of optimizing initial conditions for accurate predictions and model the possible astrophysical implications for black holes in globular clusters.

Roadmap for Readers

1. Introduction to binary systems of black holes and gravitational waves
2. Explanation of horizon flux and its effects on black hole dynamics
3. Details of the computation of horizon flux up to next-to-next-to-leading order
4. Integration of fluxes over unbound, hyperbolic-like trajectories using the TEOBResumS model
5. Discussion of the phenomenology across the parameter space and the small effects observed in most cases
6. Analysis of the analytical representation chosen for fluxes and its impact on mass and spin variations
7. Comparison of predictions with numerical relativity data of induced spins
8. Importance of optimizing initial conditions for accurate predictions
9. Possible astrophysical implications for black holes in globular clusters

Potential Challenges

• Obtaining accurate numerical relativity data for comparison
• Finding the optimal initial conditions for accurate predictions
• Selecting the most suitable analytical representation for fluxes

Potential Opportunities

• Improved understanding of the effects of horizon flux on binary black hole dynamics
• Identification of highly energetic orbits where the effects of horizon flux are significant
• Development of more precise analytical representations for fluxes in the relevant regime
• Possible advancements in modeling astrophysical implications of black holes in globular clusters

Conclusion

In summary, this work quantifies the effects of horizon flux on binary black hole dynamics and explores the phenomenology across a range of parameter space. The effects of horizon flux are generally small but become significant on highly energetic orbits. The choice of analytical representation for fluxes is crucial for accurate predictions, as demonstrated by comparisons with numerical relativity data. Optimizing initial conditions is necessary for improved agreement between predictions and data. Furthermore, this work provides insights into the possible astrophysical implications of black holes in globular clusters. Overall, this research contributes to a deeper understanding of the behavior and evolution of binary black hole systems.

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