Population of Merging Compact Binaries Inferred Using Gravitational Waves through GWTC-3
(2023) Physical Review X — Vol. 13 (2023)
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- We report on the population properties of compact binary mergers inferred from gravitational-wave observations of these systems during the first three LIGO-Virgo observing runs. The Gravitational-Wave Transient Catalog 3 (GWTC-3) contains signals consistent with three classes of binary mergers: binary black hole, binary neutron star, and neutron star–black hole mergers. We infer the binary neutron star merger rate to be between 10 and <math display="inline"><mrow><mn>1700</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>Gpc</mi></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>yr</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> and the neutron star–black hole merger rate to be between 7.8 and <math display="inline"><mrow><mn>140</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>Gpc</mi></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>yr</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>, assuming a constant rate density in the comoving frame and taking the union of 90% credible intervals for methods used in this work. We infer the binary black hole merger rate, allowing for evolution with redshift, to be between 17.9 and <math display="inline"><mrow><mn>44</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>Gpc</mi></mrow><mrow><mo>-</mo><mn>3</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>yr</mi></mrow><mrow><mo>-</mo><mn>1</mn></mrow></msup></mrow></math> at a fiducial redshift (<math display="inline"><mi>z</mi><mo>=</mo><mn>0.2</mn></math>). The rate of binary black hole mergers is observed to increase with redshift at a rate proportional to <math display="inline"><mo stretchy="false">(</mo><mn>1</mn><mo>+</mo><mi>z</mi><msup><mo stretchy="false">)</mo><mi>κ</mi></msup></math> with <math display="inline"><mi>κ</mi><mo>=</mo><mn>2.</mn><msubsup><mn>9</mn><mrow><mo>-</mo><mn>1.8</mn></mrow><mrow><mo>+</mo><mn>1.7</mn></mrow></msubsup></math> for <math display="inline"><mi>z</mi><mo>≲</mo><mn>1</mn></math>. Using both binary neutron star and neutron star–black hole binaries, we obtain a broad, relatively flat neutron star mass distribution extending from <math display="inline"><msubsup><mn>1.2</mn><mrow><mo>-</mo><mn>0.2</mn></mrow><mrow><mo>+</mo><mn>0.1</mn></mrow></msubsup></math> to <math display="inline"><msubsup><mn>2.0</mn><mrow><mo>-</mo><mn>0.3</mn></mrow><mrow><mo>+</mo><mn>0.3</mn></mrow></msubsup><msub><mi>M</mi><mo stretchy="false">⊙</mo></msub></math>. We confidently determine that the merger rate as a function of mass sharply declines after the expected maximum neutron star mass, but cannot yet confirm or rule out the existence of a lower mass gap between neutron stars and black holes. We also find the binary black hole mass distribution has localized over- and underdensities relative to a power-law distribution, with peaks emerging at chirp masses of <math display="inline"><msubsup><mn>8.3</mn><mrow><mo>-</mo><mn>0.5</mn></mrow><mrow><mo>+</mo><mn>0.3</mn></mrow></msubsup></math> and <math display="inline"><msubsup><mn>27.9</mn><mrow><mo>-</mo><mn>1.8</mn></mrow><mrow><mo>+</mo><mn>1.9</mn></mrow></msubsup><msub><mi>M</mi><mo stretchy="false">⊙</mo></msub></math>. While we continue to find that the mass distribution of a binary’s more massive component strongly decreases as a function of primary mass, we observe no evidence of a strongly suppressed merger rate above approximately <math display="inline"><mn>60</mn><msub><mi>M</mi><mo stretchy="false">⊙</mo></msub></math>, which would indicate the presence of a upper mass gap. Observed black hole spins are small, with half of spin magnitudes below <math display="inline"><msub><mi>χ</mi><mi>i</mi></msub><mo>≈</mo><mn>0.25</mn></math>. While the majority of spins are preferentially aligned with the orbital angular momentum, we infer evidence of antialigned spins among the binary population. We observe an increase in spin magnitude for systems with more unequal-mass ratio. We also observe evidence of misalignment of spins relative to the orbital angular momentum.
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., J. S., Tanasijczuk, A. J., VIRGO, LIGO Scientific, KAGRA, & et al. (2023). Population of Merging Compact Binaries Inferred Using Gravitational Waves through GWTC-3. Physical Review X, 13. https://doi.org/10.1103/PhysRevX.13.011048 (Original work published 2023)