GW241011 and GW241110: Exploring Binary Formation and Fundamental Physics with Asymmetric, High-Spin Black Hole Coalescence

TL;DR

GW241011 and GW241110 are two binary black hole mergers from the LIGO--Virgo--KAGRA network that exhibit rapidly spinning, misaligned components and unequal masses, suggesting hierarchical formation in dense stellar environments. The authors perform multi-model parameter estimation, high-order-mode and precession analyses, and tests of fundamental physics, including constraints on the Kerr spin-induced quadrupole moment, beyond-quadrupole radiation, eccentricity, and ultralight bosons via superradiance. The results provide robust, leading constraints on the Kerr nature and multipolar GW emission for GW241011, demonstrate evidence for spin–orbit misalignment in at least one system, and place new bounds on exotic particles in the $10^{-13}$–$10^{-12}$ eV range, all while situating these events within the broader BBH population. Collectively, the findings support a dynamically assembled BBH subpopulation in which repeated mergers can occur, advancing our understanding of BBH formation channels and offering new probes of gravity and particle physics with gravitational waves.

Abstract

We report the observation of gravitational waves from two binary black hole coalescences during the fourth observing run of the LIGO--Virgo--KAGRA detector network, GW241011 and GW241110. The sources of these two signals are characterized by rapid and precisely measured primary spins, non-negligible spin--orbit misalignment, and unequal mass ratios between their constituent black holes. These properties are characteristic of binaries in which the more massive object was itself formed from a previous binary black hole merger, and suggest that the sources of GW241011 and GW241110 may have formed in dense stellar environments in which repeated mergers can take place. As the third loudest gravitational-wave event published to date, with a median network signal-to-noise ratio of $36.0$, GW241011 furthermore yields stringent constraints on the Kerr nature of black holes, the multipolar structure of gravitational-wave generation, and the existence of ultralight bosons within the mass range $10^{-13}$--$10^{-12}$ eV.

Figures (21)

• Figure 1: Top: Central $90\%$ credible bounds on the dimensionless primary spins $\vec{\chi}_1$ of GW241011 (blue) and GW241110 (green), projected parallel to the direction $\hat{L}_\mathrm{N}$ of each binary's Newtonian orbital angular momentum. Shown in grey for comparison are $90\%$ credible bounds on the projected primary spins of previously-published compact binary coalescences in the fourth Gravitational-Wave Transient Catalog gwtc4, sorted by their median posterior values of $\chi_{1,z} \equiv \vec{\chi}_1 \cdot \hat{L}_\mathrm{N}$. We specifically show events with false alarm rates (FARs) below $1\,\mathrm{yr}^{-1}$, consistent with the significance threshold adopted for compact binary population studies in GWTC-3.0 and GWTC-4.0 KAGRA:2021duugwtc4-astrodist. The source of GW241011 contains one of the most rapidly spinning black holes observed by LIGO--Virgo--KAGRA to date, possessing the largest lower limit on both its primary spin magnitude and projected spin $\vec{\chi}_{1,z}$. GW241110, conversely, yields the most confident measurement to date of a black hole spinning retrograde with respect to its orbit, with $\chi_{1,z}<0$ at $97.7\%$ credibility. Bottom:$90\%$ credible posterior bounds on the primary masses and mass ratios of GW241011 and GW241110, together with all binary mergers in GWTC-4.0 with $\mathrm{FAR}<1\,\mathrm{yr}^{-1}$. Despite the opposite nature of their spins, GW241011 and GW241110 are likely to have very similar masses, each favoring a primary of $15$--$20\,M_\odot$ and unequal mass ratios.
• Figure 2: Posterior on the primary spin vector of GW241011 (left) and GW241110 (right). Within each subplot, radial coordinates span the range $0$ to $1$ and correspond to dimensionless spin magnitudes. The polar angles, spanning $0$ to $180\,\mathrm{deg}$, correspond to spin--orbit misalignment angles. Color saturation indicates posterior probability as a function of spin magnitude and orientation. Pixels are spaced linearly in spin magnitude and cosine tilt angle such that they each contain equal prior probability; a completely uninformative spin measurement would therefore yield a uniformly colored disk. GW241011 has a precisely measured spin magnitude of $\chi_1 = 0.78^{+ 0.09}_{- 0.09}$ that is misaligned by $31^{+ 11}_{- 14}\,\mathrm{degrees}$ with respect to its orbital angular momentum. The primary spin of GW241110, in contrast, is constrained to be misaligned by more than $110\,\mathrm{deg}$ from its orbital angular momentum.
• Figure 3: Posterior probabilities on selected properties of GW241011 (blue) and GW241110 (green): their primary masses $m_1$, mass ratios $q$, effective inspiral spins $\chi_\mathrm{eff}$, primary spin magnitudes $\chi_1$, and components of their primary spins projected parallel ($\chi_{1,z}$) and perpendicular ($\chi_{1,\perp}$) to each binary's Newtonian orbital angular momentum. Panels along the diagonal show marginalized posteriors on each parameter; the dashed histograms correspond to the prior probability distributions adopted during parameter estimation. Off-diagonal panels illustrate joint two-dimensional posteriors on each pair of parameters; thick and thin contours denote central $50\%$ and $90\%$ credible bounds. Shaded grey regions indicate to parts of parameter space that the constraint that spin magnitudes be less than or equal to one. Despite their extreme and opposite spins, GW241011 and GW241110 have consistent component mass measurements, each favoring a $15$--$20\,M_\odot$ primary and an unequal mass ratio.
• Figure 4: Posterior on the primary spin magnitude of GW241011 (blue). The spin of GW241011's primary black hole has the largest lower bound than that of all other merging compact objects observed to date. We obtain $\chi_1 > 0.69$ at $95\%$ credibility. For comparison, also shown are the primary spin measurements from GW231123 LIGOScientific:2025rsn and GW190517 KAGRA:2021vkt, which provide the two next-largest lower limits of $\chi_1 > 0.63$ and $\chi_1 > 0.52$, respectively.
• Figure 5: Posterior distribution on GW241011's precession SNR ratio and its SNR in $(\ell, m) = (3, \pm3)$ spherical harmonic modes. The precession SNR quantifies the observational strength of spin--orbit precession, while $(\ell, m) = (3, \pm3)$ mode radiation arises from source multipoles beyond the leading-order mass quadrupole. The unequal mass ratio and large, misaligned primary spin of GW241011 together yield $\rho_\mathrm{p} = 5.3^{+ 2.1}_{- 1.9}$ and $\rho_{33} = 5.9^{+ 1.0}_{- 1.1}$. For comparison, the dashed histogram illustrates the expected null distribution (a $\chi$-distribution with four degrees of freedom, two per detector active during GW241011) of $\rho_\mathrm{p}$ and $\rho_{33}$ in the absence of spin--orbit precession or higher-order radiation modes Prix:2007ksHarry:2010fr. This null distribution is conservative; in some cases the null distribution may take alternative forms (such as a $\chi$-distribution with fewer degrees of freedom) concentrated towards smaller SNRs Fairhurst:2019vutHoy:2021dqgHoy:2024wkc.