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The Bondi news function is the outgoing-null-time derivative of Bondi shear at future null infinity. Write the angular metric as $g_{AB}=r^2{q}_{AB}+r{C}_{AB}+O(1)$, with $q^{AB}{C}_{AB}=0$. One convention defines $N_{AB}=\frac{1}{2}{\partial }_u{C}_{AB}$; its two components encode changing gravitational-wave polarizations.

The outgoing gravitational-wave energy flux is quadratic in the news, decreasing total Bondi mass in an isolated vacuum system. Time-independent shear supplies no such flux. The shear also sets the leading detector strain at large distance.^[ref]

The Bondi-Sachs formalism uses outgoing null hypersurfaces to describe gravitational radiation. A null coordinate $u$ labels wavefronts, areal radius $r$ labels cross-sections, and angular coordinates label null generators.

The Einstein field equations split into radial relations and evolution equations for the angular geometry. At future null infinity, changing Bondi shear gives the Bondi news function, linking radiation to loss of Bondi mass in nonlinear general relativity.^[ref]

The Bondi shear is the leading trace-free angular distortion in an asymptotically flat spacetime described by Bondi-Sachs coordinates. In a common expansion, the angular metric is $h_{AB}=q_{AB}+C_{AB}/r+O(r^{-2})$, with $q^{AB}{C}_{AB}=0$.

Its retarded-time derivative determines the Bondi news function, with normalization depending on convention. The distinction matters: a nonzero but time-independent shear need not represent ongoing radiation, while changing shear describes radiative degrees of freedom. Changes between early and late configurations are also connected with gravitational memory.^[ref]