  The theoretical basis for the energy carried away by gravitational waves that
an isolated gravitating system emits was first formulated by Hermann Bondi
during the 1960s. Recent findings from looking at distant supernovae revealed
that the rate of expansion of our universe is accelerating, which may be
well-explained by sticking in a positive cosmological constant into the
Einstein field equations for general relativity. By solving the Newman-Penrose
equations (which are equivalent to the Einstein field equations), we generalise
this notion of Bondi mass-energy and thereby provide a firm theoretical
description of how an isolated gravitating system loses energy as it radiates
gravitational waves, in a universe that expands at an accelerated rate. This is
in line with the observational front of LIGO's first announcement in February
2016 that gravitational waves from the merger of a binary black hole system
have been detected.
