The 4 PI SKY research group was involved in a significant measurement of the size and associated timescales very close to the base of a black hole relativistic jet, in a project led by collaborators at The University of Southampton.
High time resolution X-ray and infrared observations during flares from the black hole V404 Cyg in 2015 revealed a ~0.1 sec time delay between the emission in the two bands. There are good arguments already that the infrared emission arises from the ‘base’ of the relativistic jet, and AMI-LA radio observations provided simultaneously by the 4 PI SKY group confirmed this. This allowed the team, led by Dr Poshak Gandhi from Southampton, to establish a size scale of ~0.1 light seconds between the X-ray emitting region (inner parts of the accretion flow) and the first synchrotron emitting zone (the jet base). The research is published in Nature Astronomy, and the article can be found on the arXiv as arXiv:1710.09838.
For the full Southampton press release (including movie!) go to: