arXiv:2505.01495v1 Announce Type: new
Abstract: We evolve for the first time in full general relativity a small, collisional N-body black hole cluster of arbitrary total mass M. The bound cluster is initially compact (radius R/M~10), stable, and consists of 25 equal-mass, nonspinning black holes. The dynamical interactions of compact objects in N-body clusters is of great interest for the formation of black holes in the upper mass gap as well as intermediate and supermassive black holes. These are potential sources of gravitational waves that may be detected by both current and future observatories. Unlike previous N-body Newtonian and post-Newtonian simulations, no “subgrid physics” is required to handle collisions and mergers. We can therefore confirm in full general relativity several predictions from these simulations and analytic estimates: the runaway growth of a large black hole via repeated mergers; spindown of the central black hole with increasing captures; the ejection of a black hole with a large asymptotic velocity due to a several-body interaction; and a regime where mergers occur primarily via direct collisions on highly eccentric orbits instead of quasicircular inspirals. We extract the gravitational wave signal and find it has several distinct features associated with the compact cluster regime. Our results suggest the signal is sufficiently loud that next generation observatories would likely be able to detect similar events across most of the observable universe. This work is a preliminary proof-of-principle study that we hope will open up a new arena for numerical relativity and the study of N-body compact systems.
Conclusions and Future Roadmap
The study of collisional N-body black hole clusters in full general relativity has yielded valuable insights into the dynamical interactions of compact objects. The results confirm several predictions and highlight the potential for detecting gravitational waves from such systems with current and future observatories. Moving forward, the following roadmap outlines potential challenges and opportunities in this field:
Potential Challenges:
- Complexity of N-body systems: As the number of black holes in a cluster increases, the computational complexity of simulating their interactions also increases, posing challenges in terms of computational resources and time.
- Accuracy of simulations: Ensuring that simulations accurately model the physics of black hole collisions and mergers in full general relativity remains a challenge, especially in the absence of subgrid physics.
- Data analysis: Extracting gravitational wave signals from simulations and interpreting them correctly requires sophisticated data analysis techniques and algorithms.
Potential Opportunities:
- New insights into black hole formation: Studying N-body clusters can provide valuable insights into the formation of black holes in the upper mass gap, intermediate, and supermassive black holes.
- Detection of gravitational waves: The distinct features of gravitational wave signals from compact clusters offer a unique opportunity to detect similar events across a wide range of distances in the universe.
- Numerical relativity advancements: This study opens up a new arena for numerical relativity, paving the way for further advancements in simulating complex gravitational systems.
This work represents a preliminary proof-of-principle study in the field of N-body compact systems. Future research in this area holds the potential to deepen our understanding of black hole dynamics and gravitational wave astronomy.