LIGO and Virgo gravity wave observatories report four more gravity wave detections. The total number of gravitational waves we have all discovered is now 11.
Ten were caused by black hole collisions and one of neutron stars collided.
The present small coating suggests:
* Black holes can be joined more often earlier in the history of the universe
* fewer collisions now involve black holes greater than about 50 times the mass of the sun  Both gravity wave detectors will be shut down until next spring to upgrade their equipment. Improvements should enable detection of three times the volume of gravity wave detections.
1; Catalog of Compact Binary Mergers Observed by LIGO and Virgo in First and Second Observations
Arxiv – GWTC-1: A Gravity-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during first and second observations.
We present the results of three gravity wave searches after merging compact binaries with component masses above 1M⊙ during the first and second observation paths of the advanced gravity wave detector network. During the first observations (O1), from September 12, 2015 to January 19, 2016, gravity waves were detected from three binary black hole assemblies. The second observation run (O2), which lasted from November 30, 2016 to August 25, 2017, saw the first discovery of gravity evenings from a binary neutron star spiral, in addition to the observation of gravity evenings from a total of seven binary black hole fusions, of which four we report here for the first time: GW170729 , GW170809, GW170818 and GW170823. For all significant gravity events, we provide estimates of the source properties. The detected binary black holes have total masses between 18.6 +3.1-0.7M⊙ and 85.1 +15.6-10.9M⊙ and the range in the range of 320 +120-110 Mpc and 2750 +1350-1320 Mpc. No neutron star – black hole fusions were detected. In addition to high-quality gravity wave events, we also provide a list of marginal conference candidates with an estimated false alert rate less than 1 per 30 days. From these results over the first two observations, which include approximately one gravity wave detection per 15 days of data being sought, we generate merge rates at 90% confidence intervals of 110 – 3840 Gpc -3 y -1 ] for binary black holes and to determine a neutron star – black hole fusion rate 90% -1 for binary neutron stars and 9.7-101 Gpc -3 upper limit of 610 Gpc -3 y -1 .