The origin of ultra-wide massive binaries ( orbital separations 10 ^ { 3 } -2 \times 10 ^ { 5 } AU ) and their properties are not well characterized nor understood .
Here we use the second Gaia data release to search for wide astrometric companions to Galactic O-B5 stars which share similar parallax and proper motion with the primaries .
Using the data we characterize the frequency and properties of such binaries .
We find an ultra-wide multiplicity fraction of 4.4 \pm 0.5 per cent , to our completeness limit ( up to \approx 17 mag ; down to G-stars at distances of 0.3-2 kpc , excluding stars in clusters ) .
The secondary mass-function is generally consistent with a Kroupa initial stellar function ; if extrapolated to lower mass companion stars we then might expect a wide-binary fraction of \sim 27 \pm 5 \% .
In addition we use these data as a verification sample to test the existence of ultra-wide binaries among neutron stars ( NSs ) and black holes ( BHs ) .
We propose that the discovery of such binary can provide unique constraints on the weakest natal kicks possible for NSs/BHs .
If a compact object is formed in an ultra-wide binary and receives a very-low natal kick , such a binary should survive as a common proper motion pair .
We therefore use Gaia data to search for ultra-wide companions to pulsars ( normal and millisecond ones ) and X-ray binaries .
We find no reliable pairs .
Future data could potentially provide stringent constraints through this method .