Phys. Rev. Lett. 116, 061102 (2016) - "Observation of Gravitational Waves from a Binary Black Hole Merger" (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102) reports that the gravitational waves detected by LIGO match up with the signal expected from two black holes merging as predicted by general relativity. Additionally, the masses of both black holes were estimated.
Also the article "Observation of Gravitational Waves from Two Neutron Star–Black Hole Coalescences" (published in 2020 January issue of the "The Astrophysical Journal Letters") states that "the LIGO–Virgo detector network observed gravitational-wave (GW) signals from two compact binary inspirals that are consistent with neutron star–black hole (NSBH) binaries. These represent the first confident observations to date of NSBH binaries via any observational means". https://iopscience.iop.org/article/10.3847/2041-8213/ac082e
How certain are we that LIGO 2016 and LIGO/VIRGO 2020 detections of gravitational waves are necessarily from two black holes merging and Neutron Star–Black Hole Coalescences (correspondingly)?
Since supermassive black holes are typically at the center of a host galaxy, what happened to the galaxies that contained the two merging black holes (when such merging is inferred only by the analysis of the structure of the registered by LIGO gravitational waves)? Is there additional (independent of gravitational waves capture analysis) observational evidence confirming that black hole's host galaxies indeed have merged.
After reading the answers, I understand that some signals (filtered from other captured signals, deemed as the background noise, because those signals do not match characteristics of gravitational wave signatures predicted by Einstein's GR) detected by LIGO are inferred as the evidence of two black holes or two neutron stars or black hole and neutron star merging as predicted by general relativity.
When additionally gravitational waves, caused by the merger of the supermassive black holes (those which ARE indeed located in the centers of the merging galaxies) will be detected, since mergers of galaxies could be observed by the methods independent of gravitational waves such as registering the fact of the quasar appearance (source).
Could someone offer me the historical ASTRONOMY precedent when the second degree of inference (from the mathematical model, being associated with the theory of Physics) was accepted as the discovery of the astronomical object?
Could someone give a reference to trustable scientific publication, with the subject of study being discussion of requirements satisfying claim of astronomical discovery of an astronomical object?
Have independent scientific sources (outside of members of the LIGO team) analyzed methodology and results of the LIGO signal detection, and published their conclusions with regards of what was actually discovered?