GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2

TL;DR

GW170104 reports a high-significance gravitational-wave detection from a heavy binary black hole coalescence at z ≈ 0.18, with component masses around 31 and 19 M_⊙ and a total mass near 51 M_⊙. Bayesian inference shows modest, broadly distributed spins with a mildly negative effective inspiral spin χ_eff, and a final remnant spinning at a ≈ 0.64; the signal is consistent with GR across multiple tests. The event refines BBH population and merger-rate estimates under two population models and strengthens constraints on gravitational-wave dispersion, including a bound on the graviton mass. Collectively, GW170104 supports multiple formation pathways for heavy BBHs and demonstrates robust GR validity in the strong-field regime, while highlighting the continued scientific value of O2 observations for population and fundamental physics studies.

Abstract

We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10:11:58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70,000 years. The inferred component black hole masses are $31.2^{+8.4}_{-6.0}\,M_\odot$ and $19.4^{+5.3}_{-5.9}\,M_\odot$ (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, $χ_\mathrm{eff} = -0.12^{+0.21}_{-0.30}.$ This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is $880^{+450}_{-390}~\mathrm{Mpc}$ corresponding to a redshift of $z = 0.18^{+0.08}_{-0.07}$. We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to $m_g \le 7.7 \times 10^{-23}~\mathrm{eV}/c^2$. In all cases, we find that GW170104 is consistent with general relativity.

Figures (15)

• Figure 1: Time--frequency representation Chatterji:2004qg of strain data from Hanford and Livingston detectors (top two panels) at the time of GW170104. The data begin at $1167559936.5$ GPS time. The third panel from top shows the time-series data from each detector with a $30$--$350~\mathrm{Hz}$ bandpass filter, and band-reject filters to suppress strong instrumental spectral lines. The Livingston data have been shifted back by $3~\mathrm{ms}$ to account for the source's sky location, and the sign of its amplitude has been inverted to account for the detectors' different orientations. The maximum-likelihood binary black hole waveform given by the full-precession model (see Sec. \ref{['s:parameters']}) is shown in black. The bottom panel shows the residuals between each data stream and the maximum-likelihood waveform.
• Figure 2: Posterior probability density for the source-frame masses $m_1$ and $m_2$ (with $m_1 \geq m_2$). The one-dimensional distributions include the posteriors for the two waveform models, and their average (black). The dashed lines mark the $90\%$ credible interval for the average posterior. The two-dimensional plot shows the contours of the $50\%$ and $90\%$ credible regions plotted over a color-coded posterior density function. For comparison, we also show the two-dimensional contours for the previous events O1:BBH.
• Figure 3: Top: Posterior probability density for the effective inspiral and precession spin parameters, $\chi_\mathrm{eff}$ and $\chi_\mathrm{p}$. The one-dimensional distributions show the posteriors for the two waveform models, their average (black), and the prior distributions (green). The dashed lines mark the $90\%$ credible interval for the average posterior. The two-dimensional plot shows the $50\%$ and $90\%$ credible regions plotted over the posterior density function. Bottom: Posterior probabilities for the dimensionless component spins, $c\mathbf{S}_1/(Gm_1^2)$ and $c\mathbf{S}_2/(Gm_2^2)$, relative to the normal of the orbital plane $\mathbf{\hat{L}}$. The tilt angles are $0^\circ$ for spins aligned with the orbital angular momentum and $180^\circ$ for spins antialigned. The probabilities are marginalized over the azimuthal angles. The pixels have equal prior probability ($1.6\times10^{-3}$); they are spaced linearly in spin magnitudes and the cosine of the tilt angles. Results are given at a gravitational-wave frequency of $20~\mathrm{Hz}$.
• Figure 4: Time-domain detector data (gray), and $90\%$ confidence intervals for waveforms reconstructed from the morphology-independent wavelet analysis (orange) and binary black hole (BBH) models from both waveform families (blue), whitened by each instrument's noise amplitude spectral density. The left ordinate axes are normalized such that the amplitude of the whitened data and the physical strain are equal at $200~\mathrm{Hz}$. The right ordinate axes are in units of noise standard deviations. The width of the BBH region is dominated by the uncertainty in the astrophysical parameters.
• Figure 5: $90\%$ credible upper bounds on $|A|$, the magnitude of dispersion, obtained combining the posteriors of GW170104 with those of GW150914 and GW151226. We use picoelectronvolts as a convenient unit because the corresponding frequency scale is around where GW170104 has greatest amplitude ($1~\mathrm{peV} \simeq h \times 250~\mathrm{Hz}$, where $h$ is the Planck constant). General relativity corresponds to $A=0.$ Markers filled at the top (bottom) correspond to values of $|A|$ and $\alpha$ for which gravitational waves travel with superluminal (subluminal) speed.