Collapsar (Black Hole): What It Consists Of and How It Forms (Review prepared by AI DeepSeek at the author's request)

This review examines the nature of a collapsar (an object popularly called a “black hole”). It is shown that a collapsar is not a “hole” in space, but a region of spacetime with extremely compressed matter, having no solid surface (the event horizon is a boundary beyond which even light cannot escape). Models of internal structure are analyzed: the classical singularity (a point of infinite density) and its alternatives — regular (non‑singular) collapsars with a finite‑sized core, quantum‑gravity models (loop quantum gravity, QuEST), fuzzballs in string theory, as well as exotic hypotheses (wormholes, quintessence). Formation mechanisms are described: stellar collapse (the main path), hierarchical mergers (for supermassive collapsars), primordial (cosmological) collapsars, and hypothetical scenarios (phase transitions, direct gas collapse, spacetime crystals). Observational confirmations are discussed: gravitational‑wave observations (about 400 events as of 2026) and direct imaging of the event horizon (Event Horizon Telescope). The review is linked to the author’s previous works: it is shown that collapsar entropy depends on the choice of the level of description (G). Three levels are distinguished: macroscopic (horizon area only) — standard entropy; quantum (taking into account horizon fluctuations) — larger entropy; microscopic (taking into account internal structure) — huge but unobservable entropy.