This paper published in 1969 indicates that a majority of the mass-energy of the universe may be contained in gravitational waves:

"Turning next to phenomena on a galactic scale, we find it conceivable that over the past ~10^10 years the Galaxy may have radiated away as much as 10 times its present mass."

Has the reasoning in the paper been refuted by actual gravitational wave detections over the past decade?

Apparently two merging solar mass scale black holes of about the same size lose about 5% of their mass to gravitational radiation. I'm not sure how that percentage scales with mass, but assuming it does not change with mass as long as the black holes are approximately the same size, it would be possible to convert a very high percentage of the mass of an initial distribution of stellar-mass black holes into gravitational radiation. E.g., if pairs of stellar-mass BHs, then pairs of ~2 stellar mass BHs, then pairs of ~4 stellar mass BHs and so on are merged, with 5% of the mass radiated away each time, ~65% (1-0.95^20) of the mass would be radiated away by the time a million-stellar-mass supermassive black hole is formed. Some supermassive black holes are as large as 10 billion stellar masses, which would allow ~84% of the mass to be radiated away.

Added 6/26/20: Mass loss could possibly provide a component of cosmological expansion. If two objects are orbiting each other and then lose mass, their orbits should expand. It seems that if a cluster of gravitationally interacting bodies - stars or galaxies - lose mass, then the cluster should expand.

  • $\begingroup$ I want to point out that the formation of supermassive black hole by stellar black hole mergers is very unlikely, if not impossible $\endgroup$ – AnOrAn Jun 18 at 20:40
  • $\begingroup$ Correct me if I'm wrong, but it seems to me the article and the estimates are based on those Weber observations cited there? Those observations were duplicated many times and always gave a null result. You can find more infos here: en.m.wikipedia.org/wiki/Weber_bar $\endgroup$ – AnOrAn Jun 18 at 20:48
  • $\begingroup$ I'm sure you're right about that. The reasoning is what I'm curious about. $\endgroup$ – S. McGrew Jun 18 at 21:02
  • $\begingroup$ I always assumed that when mass is lost, the curvature it caused is "relaxed" as it were and this ripples outwards as the associated gravity wave. Positive energy lost by the objects is balanced by negative energy lost via the relaxation. Am I wrong? $\endgroup$ – Guy Inchbald Jun 26 at 16:03
  • $\begingroup$ I'm just imagining what would happen if, e.g., the masses of the Earth and Moon were abruptly reduced by, say, 50%. Both bodies would be moving too fast relative to the common center of mass to continue in their circular orbits, so the orbits would change to ellipses that extend beyond the original orbital radii. $\endgroup$ – S. McGrew Jun 26 at 16:13

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