LIGO-O3Catalog And Pop

LIGO, Virgo, and KAGRA provide a comprehensive report and discussion of the compact binaries found during the third observing run. We’ve found a lot this run: neutron star black hole binaries (GW200105 and 200115); big black holes (GW190521); and several binaries likely containing neutron stars. We’ve learned a lot about what nature produces in our local universe, and even a little about how the faraway universe looks somewhat different than the universe nearby. (Short version: more mergers as we go back in time, so far.)

This carefully conducted census of merging objects in the nearby universe reveals some interesting surprises. We find neutron stars in merging binaries can have a wide range of masses, unlike the neutron stars in merging binaries in our own galaxy. Conversely, we find certain types of binary black holes are more likely than others with comparable masses. We’re able to measure the merger rate versus mass over the whole mass plane LIGO’s sensitive to, letting us paint a single picture of merging objects from neutron stars up to the most massive black holes we’ve seen. In that picture, we see hints of some gaps, for example between black hole and neutron star masses.

For experts:Why should you care? Black hole masses seem to cluster, but without a corresponding signature in the spin distribution that you’d expect from hierarchical grown. Observed black hole spins are mostly small, being particularly well constrained to be near zero at low mass (and for the most asymmetric binaries); conversely, some very large black holes are likely spinning. We still stand by our previous claims that the black hole population shows signs of precession, after carefully considering counterproposals in the literature. We hadn’t fully appreciated how much modeling systematics impacted some of our merger rate estimates, notably for BNS, so our error bars can be more conservative than before.

For more information:

• GWTC-3 catalog, submitted to PRX, with a public data release available at LIGO DCC; see also the GW open science center.

• The population of merging compact binaries inferred using gravitational waves through GWTC-3, also with an associated data release.

You can find all of the papers which LIGO and Virgo released this week at papers.ligo.org.

RIFT and the O3 catalog: Our parameter inference code RIFT was once again widely used in GWTC-3

PopModels and the O3 population: RIT-developed PopModels was one of the tools used to infer the population of merging binaries.