Bondi news function ($N_{AB}$)

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]