A4 Black Holes and Horizons

Topic

The central elements of this model are the black hole and the matter falling into it. A black hole is a region of spacetime curved so intensely that no signal can escape once it crosses the defining event horizon.

The accretion of matter onto a black hole is the most efficient energy-release mechanism known in the universe—far surpassing the energy released by nuclear fusion—and this efficiency is even greater when the black hole itself rotates rapidly.

The accretion disk surrounding the black hole emits radiation at a temperature that drops sharply as the radius within the disk increases; consequently, the disk's inner edge—located at the innermost stable orbit—is by far the hottest region of the entire accretion disk.

Stellar-mass black holes result from the core-collapse process described elsewhere as a distinct model, and they are detected specifically within X-ray binary systems. In contrast, supermassive black holes—millions to billions of times more massive than the Sun—reside at the centers of virtually all massive galaxies; the close correlation observed between the mass of these black holes and the velocity dispersion of stars in the surrounding galactic bulge suggests that the black hole and its host galaxy grew in tandem throughout cosmic history.

Direct imaging of the shadow cast by the event horizon onto surrounding material has confirmed the extreme geometry predicted by general relativity for two distinct supermassive black holes. Thus, from the region of spacetime where this document begins to the confirmed geometry with which it concludes—encompassing accretion efficiency and the correlation between the supermassive black hole and its host galaxy—the black hole ensures that the most extreme end state of the entire gravitational chain still casts a shadow capable of being photographed.

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