Dendro-GR at high mass ratios with high spins

Abstract

The Laser Interferometer Space Antenna (LISA) launches in less than a decade; it will detect spinning high-mass-ratio binary black hole inspirals annually, alongside other third-generation gravitational wave detectors. High-mass-ratio systems occupy a regime where numerical-relativity simulations remain computationally expensive and technically demanding, especially with high spins at precessing orientations. This portion of parameter space thus remains undersampled, leading to significant bias in parameter estimation. We must close these gaps. Here we report key progress in Dendro-GR toward reducing the computational cost of high-mass-ratio binaries with spin. We evolve the first Dendro-GR binaries at mass ratio $q=24$ (nonspinning) and at $q=12$ with spins up to $χ=0.8$ on both black holes, spanning various configurations. These proof-of-concept runs show strong evidence that Dendro-GR can simulate in this regime and beyond. The simulations generate accurate gravitational waveforms through multipole modes up to $\ell=8$, remain stable, keep constraint violations low and largely constant, conserve horizon mass, and have high computational efficiency with relatively low wall-hour cost. These results establish our starting line for systematic exploration of the high-mass-ratio, high-spin binary black hole systems that are needed for gravitational wave analysis.