Properties of the Binary Black Hole Merger GW150914 (1602.03840v2)

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.

• The paper presents a Bayesian analysis that robustly estimates the binary black hole component masses, spins, and emitted energy.
• It employs advanced EOBNR and IMRPhenom waveform models to infer precise source parameters under strong gravitational fields.
• The study validates general relativity's predictions and constrains black hole spin, offering key insights into binary evolution and merger rates.

An Analysis of the Binary Black Hole Merger GW150914

The paper "Properties of the Binary Black Hole Merger GW150914" published in Physical Review Letters presents a comprehensive analysis of the first direct detection of gravitational waves (GWs) by the LIGO observatory. The detection, designated GW150914, marks a significant milestone, confirming the merger of a binary black hole (BBH) system. It reveals insights into gravitational wave astronomy and stellar-mass black hole properties, further validating general relativity's predictions in this strong-field regime.

Summary of Findings

Detected on September 14, 2015, GW150914 originated from a BBH merger with component masses of approximately 36 and 29 solar masses (M⊙), respectively. The final black hole, post-merger, was estimated to have a mass of about 62 M⊙ and a dimensionless spin of 0.67. This event is notable for involving component masses significantly heavier than those found in x-ray binary systems. The system radiated approximately 3 M⊙c² worth of energy in gravitational waves, which corresponds to a peak luminosity of around 3.5 x 10⁵⁶ ergs/s, showcasing the immense power of such cosmic events.

Methodological Approach

The analysis applied coherent Bayesian framework techniques across the LIGO detectors, utilizing advanced waveform models to infer source parameters. Two classes of waveform models were emphasized: Effective-One-Body Numerical Relativity (EOBNR) and Inspiral-Merger-Ringdown Phenomenological (IMRPhenom). Both frameworks incorporated general-relativistic effects, including the black hole spins, providing confidence in the derived source parameters.

Implications and Interpretation

Astrophysical Significance:

The GW150914 event signifies compelling evidence of stellar-mass BBHs in the universe consistently merging within a Hubble time, reinforcing the notion that such mergers could be a common phenomenon. This discovery also facilitates a deeper understanding of binary star evolution and contributes to estimating BBH merger rates, with significant implications for population synthesis models and gravitational wave astrophysics.

Determining Spin Properties:

One of the most significant findings is the constraints on black hole spins. The paper bounds the primary black hole's dimensionless spin below 0.7 with 90% confidence, and observes no maximal spin scenarios. Spin constraints provide insights into the evolutionary channels of BBHs, distinguishing between different formation scenarios (such as field binaries vs. dynamic captures).

General Relativity Tests:

GW150914 presents an unprecedented opportunity to test the predictions of general relativity, especially in the dynamical and strong-field limits. The observed signal was found consistent with general relativity's predictions, supporting its robustness even in conditions of extreme gravity.

Future Prospects

The analysis of GW150914 heralds a new era in GW astronomy, with LIGO's ability to detect similarly strong and diverse signals anticipated to grow as observational capabilities improve. Future detections will improve constraints on black hole populations and properties, enable a refined understanding of BBH formation and evolution, and provide further stringent tests of fundamental physics. Enhanced detector sensitivities and expanded detector arrays (including Virgo and other global facilities) promise to yield more frequent detections, enhancing source localization and parameter estimation fidelity.

Conclusion

This paper establishes GW150914 as a critical probing tool in astrophysics and fundamental physics, highlighting LIGO's instrumental role. The paper stands as a testament to the collaboration's successful global efforts in opening an entirely new observational window, making gravitational waves a pivotal aspect of modern astronomy. This initial detection catalyzes ongoing research into universal gravitational phenomena, continually enhancing our understanding of the cosmos.