# How much mass is in gravitational waves?

Like photons, I understand gravitational waves to have no rest mass but mass due to their energy. Are gravitational waves a significant part of total mass and what are the main components (black hole collisions, big bang etc)?

• please note that a bunch of collinear photons have zero mass. It is the "length" of the sum of all the fourvectors of the individual photons: the invariant mass, that characterizes a beam of photons building up a classical em waver , or a beam of gravitons( presuming wuantizatiin of gravity) building up a classical gravitional wave. – anna v Jul 30 '18 at 14:19
• The only useful concept of mass is rest mass. What you are calling mass is energy divided by $c^2$. As to your question, reformulated as how much energy is gloating around as gravitational waves, that is still to be found out. – my2cts Jul 30 '18 at 16:48

Turning to the very useful cosmic energy inventory by Peebles and Fukugita, they estimate that gravitational radiation from massive black holes make up $10^{-7.5\pm 0.5}$ of the total energy of the universe, stellar binaries contribute the smaller $10^{-9\pm 1}$ and primeval gravitational waves are less than $10^{-10}$.
In short, they make up a rather small component. As comparison, they estimate stars to make up 0.0015 and planets $10^{-6}$ of the energy.