Absorption of Gravitational Waves from Distant Sources
  The rate of gravitational wave absorption by inverse bremsstrahlung is
calculated. It increases with decreasing frequency $\nu$ as $\nu^{-3}$.
Nevertheless, because of the near cancellation of absorption by stimulated
emission, the ionized gas in galaxy clusters does not block gravitational waves
at the nanohertz frequencies that may be detected by the use of pulsar timing
observations.
