Ultrarelativistic limit of the boosted Schwarzschild metric away from the null plane
= Ultrarelativistic limit of the boosted Schwarzschild metric away from the null plane
{c}
Boost a Schwarzschild mass with speed $v$ and hold $p=m\gamma$ fixed as $v\to1$. Away from the null plane $x=t$, the isotropic-coordinate expression tends to
$$
ds^2=ds_{\rm Minkowski}^2+\frac{4p}{|x-t|}(dt-dx)^2.
$$
The complete distributional limit on the null plane requires the additional coordinate treatment that produces the Aichelburg-Sexl shock wave.