We can only rely on observations we can make. I once read a sci fi story where they used a miniature black hole as a gravity wave transmitter. Mini black holes could have formed during the big bang. Gravity waves were not measured yet directly, but observations of many binary systems are fully consistent with the expectations. A project called LIGO will measure them directly in the near future.
Gravity waves travel at the speed of light.
Being a retired physicist, myself, you can get as detailed technically as you wish. Unfortunately, optical spectra analysis was not my specialty. The relative abundances of many elements are determined from the spectra of supernovae. Read more questions and answers.