A billion years ago, two black holes spiraled together, forming a new black hole. They produced gravitational waves that reached Earth on September 14, 2015, where they were measured during the first ...observing run of the Advanced LIGO detectors. This signal marked the birth of gravitational-wave astronomy, which provides a unique way to study black holes and neutron stars. The Advanced LIGO and Advanced Virgo detectors have now completed their third observing run, the latest in a series of runs, each more sensitive (and with higher detection rates) than the last. Here, we present the third Gravitational-Wave Transient Catalog (GWTC-3), which describes discoveries made up to the end of the third run.GWTC-3 contains 90 gravitational-wave candidates—35 more than the previous catalog—with better-than-even odds of being real signals. The catalog is an unprecedented census of merging black holes and neutron stars. We now have observations of binary neutron stars, binary black holes, and neutron star–black hole binaries. These cover a diverse range of masses, from neutron stars as light as 1.2 solar masses to remnant black holes exceeding 100 solar masses, and include ambiguous objects that straddle the expected divide between neutron stars and black holes.This paper details the latest results from the third observing run, from detector status and data-quality checks, to searches for signals and source-property inferences. GWTC-3 observations and associated data enable studies of compact astrophysical objects, the nature of gravity, and the history of the Universe. However, many puzzles and open questions remain to be addressed by future observing runs, which promise to yield hundreds more binary detections and possibly entirely new types of gravitational-wave sources.
We report on the population properties of 76 compact binary mergers detected with gravitational waves below a false alarm rate of 1 per year through GWTC-3. The catalog contains three classes of ...binary mergers: BBH, BNS, and NSBH mergers. We infer the BNS merger rate to be between 10 $\rm{Gpc^{-3} yr^{-1}}$ and 1700 $\rm{Gpc^{-3} yr^{-1}}$ and the NSBH merger rate to be between 7.8 $\rm{Gpc^{-3}\, yr^{-1}}$ and 140 $\rm{Gpc^{-3} yr^{-1}}$ , assuming a constant rate density versus comoving volume and taking the union of 90% credible intervals for methods used in this work. Accounting for the BBH merger rate to evolve with redshift, we find the BBH merger rate to be between 17.9 $\rm{Gpc^{-3}\, yr^{-1}}$ and 44 $\rm{Gpc^{-3}\, yr^{-1}}$ at a fiducial redshift (z=0.2). We obtain a broad neutron star mass distribution extending from $1.2^{+0.1}_{-0.2} M_\odot$ to $2.0^{+0.3}_{-0.3} M_\odot$. We can confidently identify a rapid decrease in merger rate versus component mass between neutron star-like masses and black-hole-like masses, but there is no evidence that the merger rate increases again before 10 $M_\odot$. We also find the BBH mass distribution has localized over- and under-densities relative to a power law distribution. While we continue to find 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 $\sim 60 M_\odot$. The rate of BBH mergers is observed to increase with redshift at a rate proportional to $(1+z)^{\kappa}$ with $\kappa = 2.9^{+1.7}_{-1.8}$ for $z\lesssim 1$. Observed black hole spins are small, with half of spin magnitudes below $\chi_i \simeq 0.25$. We observe evidence of negative aligned spins in the population, and an increase in spin magnitude for systems with more unequal mass ratio.
Here, we present a search for subsolar mass ultracompact objects in data obtained during Advanced LIGO's second observing run. In contrast to a previous search of Advanced LIGO data from the first ...observing run, this search includes the effects of component spin on the gravitational waveform. We identify no viable gravitational-wave candidates consistent with subsolar mass ultracompact binaries with at least one component between $0.2 M_{⊙}-1.0 M_{⊙}$. We use the null result to constrain the binary merger rate of ($0.2 M_{⊙}, 0.2 M_{⊙}$) binaries to be less than $3.7×10^{5} Gpc^{-3} yr^{-1}$ and the binary merger rate of ($1.0 M_{⊙}, 1.0 M_{⊙}$) binaries to be less than $5.2×10^{3} Gpc^{-3} yr^{-1}$. Subsolar mass ultracompact objects are not expected to form via known stellar evolution channels, though it has been suggested that primordial density fluctuations or particle dark matter with cooling mechanisms and/or nuclear interactions could form black holes with subsolar masses. Assuming a particular primordial black hole (PBH) formation model, we constrain a population of merging $0.2 M_{⊙}$ black holes to account for less than 16% of the dark matter density and a population of merging $1.0 M_{⊙}$ black holes to account for less than 2% of the dark matter density. We discuss how constraints on the merger rate and dark matter fraction may be extended to arbitrary black hole population models that predict subsolar mass binaries.
The LIGO Scientific and Virgo Collaborations have announced the event GW170817, the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron ...stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star component will add to the contribution from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude Ω_{GW}(f=25 Hz)=1.8_{-1.3}^{+2.7}×10^{-9} with 90% confidence, compared with Ω_{GW}(f=25 Hz)=1.1_{-0.7}^{+1.2}×10^{-9} from binary black holes alone. Assuming the most probable rate for compact binary mergers, we find that the total background may be detectable with a signal-to-noise-ratio of 3 after 40 months of total observation time, based on the expected timeline for Advanced LIGO and Virgo to reach their design sensitivity.
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