Theoretical calculations predict an event horizon to all black holes, obscuring the central region in accordance with General Relativity. This is a prediction that has never been tested observationally. Image credit:
Ute Kraus, Physics education group Kraus, Universität Hildesheim; Axel Mellinger (background).

Earth prepares to snap first-ever image of a black hole’s event horizon

We’ve never seen an event horizon, nor directly imaged a black hole. Thanks to a worldwide effort, victory may at last be in sight.

“Never look down to test the ground before taking your next step; only he who keeps his eye fixed on the far horizon will find the right road.”
-Dag Hammarskjold

Perhaps gravity’s oddest prediction is the existence of black holes: regions of space where gravity is so strong that nothing, not even light, can escape.

Only through gravitational effects, such as by influencing stars, have they ever been seen.

The core of galaxy NGC 4261, like the core of a great many galaxies, show signs of a supermassive black hole in both infrared and X-ray observations. The evidence for a supermassive black hole is strong, but indirect. Image credit: NASA / Hubble and ESA.

X-ray signatures can locate and be used to weigh black holes as well, but that evidence is indirect.