The photon sphere and the shadow

node

The radius at which light itself can orbit. For a non-rotating black hole it sits at one and a half times the Schwarzschild radius, and it is unstable: a photon there falls in or escapes at the slightest perturbation. This surface, not the horizon, is what an image of a black hole actually outlines. Rays passing near it are bent so strongly that a distant observer sees a dark region whose angular radius corresponds to the square root of twenty-seven times GM over c-squared - a shadow whose diameter is about 5.2 Schwarzschild radii, roughly 2.6 times the diameter of the horizon inside it. The bright rim is a photon ring built from light that looped one or more times around the hole before escaping; successive sub-rings are exponentially thinner and fainter, by a factor close to e-to-the-pi for the non-rotating case. Because the shadow diameter depends only on mass and distance, measuring it measures the mass. Not a place on Earth.

A node is not a place. Drawing it on a map would assert something about the world that no stored fact supports.