Properties of the Binary Black Hole Merger GW150914

TL;DR

GW150914 represents the first confirmed binary black hole merger detected via gravitational waves. The authors perform a Bayesian, multi-model analysis that coherently combines data from the LIGO detectors using spin-sensitive BBH waveform families (EOBNR and IMRPhenomPv2) while accounting for calibration uncertainties. They infer robust source parameters: component masses around $m_1^{\text{source}}=36^{+5}_{-4}\,M_\odot$ and $m_2^{\text{source}}=29^{+4}_{-4}\,M_\odot$, a remnant BH of $M_f^{\text{source}}=62^{+4}_{-4}\,M_\odot$ with $a_f\approx0.67$, located at $D_L=410^{+160}_{-180}$ Mpc ($z\approx0.09$), and radiating about $3.0^{+0.5}_{-0.4}\,M_\odot c^2$ in GWs. The analysis shows broad agreement between waveform families, supports the interpretation as a BBH merger within GR, and demonstrates the power of gravitational-wave astronomy to probe stellar-mass black holes and their formation channels.

Abstract

On September 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) detected a gravitational-wave transient (GW150914); we characterize the properties of the source and its parameters. The data around the time of the event were analyzed coherently across the LIGO network using a suite of accurate waveform models that describe gravitational waves from a compact binary system in general relativity. GW150914 was produced by a nearly equal mass binary black hole of $36^{+5}_{-4} M_\odot$ and $29^{+4}_{-4} M_\odot$; for each parameter we report the median value and the range of the 90% credible interval. The dimensionless spin magnitude of the more massive black hole is bound to be $<0.7$ (at 90% probability). The luminosity distance to the source is $410^{+160}_{-180}$ Mpc, corresponding to a redshift $0.09^{+0.03}_{-0.04}$ assuming standard cosmology. The source location is constrained to an annulus section of $610$ deg$^2$, primarily in the southern hemisphere. The binary merges into a black hole of $62^{+4}_{-4} M_\odot$ and spin $0.67^{+0.05}_{-0.07}$. This black hole is significantly more massive than any other inferred from electromagnetic observations in the stellar-mass regime.

Figures (6)

• Figure 1: Posterior PDFs for the source-frame component masses$m_{1}^{\text{source }}$ and $m_{2}^{\text{source }}$. We use the convention that $m_{2}^{\text{source }} \leq m_{1}^{\text{source }}$, which produces the sharp cut in the two-dimensional distribution. In the one-dimensional marginalized distributions we show the Overall (solid black), IMRPhenom (blue), and EOBNR (red) PDFs; the dashed vertical lines mark the $90 \%$ credible interval for the Overall PDF. The two-dimensional plot shows the contours of the $50 \%$ and $90 \%$ credible regions plotted over a color-coded PDF.
• Figure 2: Posterior PDFs for the source luminosity distance$D_{L}$ and the binary inclination $\theta_{J N}$. In the one-dimensional marginalized distributions we show the Overall (solid black), IMRPhenom (blue), and EOBNR (red) PDFs; the dashed vertical lines mark the $90 \%$ credible interval for the Overall PDF. The two-dimensional plot shows the contours of the $50 \%$ and $90 \%$ credible regions plotted over a color-coded PDF.
• Figure 3: PDFs for the source-frame mass and spin of the remnant BH produced by the coalescence of the binary. In the onedimensional marginalized distributions we show the Overall (solid black), IMRPhenom (blue), and EOBNR (red) PDFs; the dashed vertical lines mark the$90 \%$ credible interval for the Overall PDF. The two-dimensional plot shows the contours of the $50 \%$ and $90 \%$ credible regions plotted over a color-coded PDF.
• Figure 4: An orthographic projection of the PDF for the sky location of GW150914 given in terms of right ascension$\alpha$ (measured in hours and labeled around the edge of the figure) and declination $\delta$ (measured in degrees and labeled inside the figure). The contours of the $50 \%$ and $90 \%$ credible regions are plotted over a color-coded PDF. The sky localization forms part of an annulus, set by the time delay of $6.9_{-0.4}^{+0.5} \mathrm{~ms}$ between the Livingston and Hanford detectors.
• Figure 5: Left: PDFs (solid black line) for the$\chi_{p}$ and $\chi_{\text{eff }}$ spin parameters compared to their prior distribution (green line). The dashed vertical lines mark the $90 \%$ credible interval. The one-dimensional plots show probability contours of the prior (green) and marginalized PDF (black). The two-dimensional plot shows the contours of the $50 \%$ and $90 \%$ credible regions plotted over a color-coded PDF. Right: PDFs for the dimensionless component spins $c \boldsymbol{S}_{1} /\left(G m_{1}^{2}\right)$ and $c \boldsymbol{S}_{2} /\left(G m_{2}^{2}\right)$ relative to the normal to the orbital plane $\boldsymbol{L}$, marginalized over uncertainties in the azimuthal angles. The bins are constructed linearly in spin magnitude and the cosine of the tilt angles, $\cos \theta_{L S_{i}}=\boldsymbol{S}_{i} \cdot \boldsymbol{L} /\left(\left|\boldsymbol{S}_{i}\right||\boldsymbol{L}|\right)$, where $i=\{1,2\}$, and therefore have equal prior probability.