I do understand that nothing, no particles and no information can escape a BH.
Gravitational waves are real, they have been observed.
Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses, that propagate as waves outward from their source at the speed of light.On 11 February 2016, the LIGO and Virgo Scientific Collaboration announced they had made the first direct observation of gravitational waves. The observation was made five months earlier, on 14 September 2015, using the Advanced LIGO detectors. The gravitational waves originated from a pair of merging black holes. After the initial announcement the LIGO instruments detected two more confirmed, and one potential, gravitational wave events. In August 2017, the two LIGO instruments and the Virgo instrument observed a fourth gravitational wave from merging black holes, and a fifth gravitational wave from a binary neutron star merger. Several other gravitational wave detectors are planned or under construction.
Now GWs are said to couple to matter much much weaker then EM waves, thus GWs experience much less scattering or absorption, GWs should be unaffected by the opacity of the early universe.
Due to the weakness of the coupling of gravity to matter, gravitational waves experience very little absorption or scattering, even as they travel over astronomical distances. In particular, gravitational waves are expected to be unaffected by the opacity of the very early universe. In these early phases, space had not yet become "transparent," so observations based upon light, radio waves, and other electromagnetic radiation that far back into time are limited or unavailable. Therefore, gravitational waves are expected in principle to have the potential to provide a wealth of observational data about the very early universe.
Now GWs are said to have a property that even EM do not have, that is GWs can pass through any intervening matter without being scattered.
Second, gravitational waves can pass through any intervening matter without being scattered significantly. Whereas light from distant stars may be blocked out by interstellar dust, for example, gravitational waves will pass through essentially unimpeded.
I do understand that nothing, no particle, no information can escape a BH. There is still no consensus about whether GWs are made of gravitons (hypothetical) or not. GWs are basically disturbances in the curvature of spacetime.
In general relativity, there is no dispersion in gravitational waves, while some modified gravity theories predict dispersion phenomena in the propagation of gravitational waves. In this Letter, we demonstrate that this dispersion will induce an observable deviation of waveforms if the orbits have large eccentricities. The mechanism is that the waveform modes with different frequencies will be emitted at the same time due to the existence of eccentricity. During the propagation, because of the dispersion, the arrival time of different modes will be different, then produce the deviation and dephasing of waveforms compared with general relativity.
The fact that GWs can pass through any matter without being scattered significantly could mean that GWs (being just distortions of the curvature of spacetime itself) could pass through BHs, and carry information on the inside of the BH.
A BH itself represents an extreme distortion of curvature at the EH of the BH, and GWs are themselves distortions of the same curvature of spacetime.
- Can we use GWs to investigate the inside of BHs?