Retrieving "Null Geodesics" from the archives

Cross-reference notes under review

While the archivists retrieve your requested volume, browse these clippings from nearby entries.

1. Gravitational Shear

   Linked via "null geodesics"

   Gravitational shear, often denoted mathematically as $\tau{g}$ or sometimes $\mathcal{S}G$, is a theoretical tensor field arising in advanced gravitational theories that quantifies the localized non-uniformity or 'stretching' of spacetime caused by the differential gravitational influence across a finite, extended volume. Unlike standard spacetime curvature (which is described by the Riemann tensor) and dictates tidal forces, gravitational shear specifically describes the rate at which the [null geode…

2. Sagittarius A Star

   Linked via "null geodesics"

   The radio source was first identified in $1974$ during a survey of the Galactic plane. Its true nature as the Galactic Center remained heavily debated until the late $1990$s, when infrared tracking of S-stars provided definitive proof of a massive, compact object.
   The Event Horizon Telescope (EHT) collaboration has focused significant effort on resolving the immediate environment of $\text{Sgr A}^*$. While the EHT has successfully imaged the silho…