Superradiance Constraints from GW231123

Abstract

Gravitational wave observations have recently revealed with high significance, and high precision, the existence of $\mathcal{O}(100) \, M_\odot$ rapidly rotating black holes, allowing gravitational wave events to be used for the first time to probe unexplored axion parameter space using the phenomenon known as black hole superradiance. Here, we present new limits on axions using the binary black hole merger event GW231123, whose constituent black holes are among the fastest spinning observed with gravitational waves to date. We demonstrate that the most viable binary formation channels lead to conservative constraints on axion masses $μ\sim [0.6-5] \times \, 10^{-13}$ eV and decay constants $f_Φ\gtrsim 10^{14}$ GeV, extending existing superradiance constraints derived using x-ray observations to yet lower axion masses.

Figures (8)

• Figure 1: Constraint on the axion decay constant $f_\Phi$ and mass $\mu$ derived from GW231123 (blue); result is obtained using NRSur waveform model analysis, using $N_{\rm max}=5$, and with $\tau_{\rm max} = 10^5$ (shaded), $10^6$ (dashed), and $10^7$ years (dot-dashed). Shown for comparison are superradiance constraints on solar-mass scale BHs Witte:2024drg, with spin inferences performed using x-ray data (black), the QCD axion line (red), and the parameter space where misalignment mechanism could produce the entirety of dark matter with $\mathcal{O}(1)$ initial field values (green). The inverse Planck scale $M_{\rm Pl}$ is highlighted with a horizontal dashed line.
• Figure 2: Comparison of limits obtained using NRSur and Combined posterior samples from LVK analysis. Results are shown for $\tau_{\rm max} = 10^6$ and $10^7$ years.
• Figure 3: Left: Comparison of limits obtained using NRSur, $N_{\rm max } = 3$, and maximum timescales $\tau_{\rm max} = 10^5, 10^6,$ and $10^7$ years. Right: Comparison of limits obtained using NRSur (purple) and Combined (blue) posterior samples from LVK analysis, fixing $\tau_{\rm max} = 10^6$, and taking both $N_{\rm max} = 3$ (solid) and $N_{\rm max} = 5$ (dashed).
• Figure 4: Comparison of limits obtained using only the heavy BH (purple), or using both BHs (blue). Here, we take the NRSur posterior samples, $N_{\rm max} = 3$ (left) and $N_{\rm max} = 5$ (right), and $\tau_{\rm max} = 10^6$ (left) and $10^5$ years (right).
• Figure 5: Comparison of limits obtained for $N_{\rm max} = 3$ and $\tau_{\rm max} = 10^5$ years, with those obtained by truncating the prior for spins $\tilde{a} \gtrsim 0.89$. Both runs are made using NRSur posterior samples.