edit: Thanks to the comment below - I learned that the PLR is available to read http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.241103. In it, ref. 5 links to this preprint dated June15, 2016: Binary Black Hole Mergers in the first Advanced LIGO Observing Run https://dcc.ligo.org/public/0124/P1600088/015/bbh-o1.pdf.

This BBC article dated June 15, 2016 More gravitational waves detected states:

Reporting the event in the journal Physical Review Letters, the international collaboration that operates LIGO says the two objects involved had masses that were 14 and eight times that of our Sun.

The data indicates the union produced a single black hole of 21 solar masses, meaning they radiated pure energy to space equivalent to the mass of one star of Sun size.

It is this energy, in the form of gravitational waves, that was sensed in the laser interferometers of the LIGO labs...

Nuclear reactions and decays can result in mass changes of the order of a part per thousand or less, and matter/antimatter particle-antiparticle annihilation can change all of the mass to light. But in this case, really - 5% of the mass was (believed to have been) converted to energy in the form of gravitational waves? I mean black holes can potentially evaporate if they manage to stop "eating" long enough, but these waves seem to just spread out into something that stops having a significant effect on anything.

my question: So 5% of the mass of a pair of black holes is (believed to have been) actually converted all the way to energy in the form of vibration of space? If so, what is the experimental uncertainty on the mass - where is it indicated and the calculation of this value discussed?