Astronomical black holes

Astronomical black holes are regions of spacetime bounded by event horizons, beyond which nothing can escape to distant observers. They are detected through their effects on nearby matter, light, and gravitational waves.

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Event horizon: A boundary in spacetime beyond which events cannot influence distant observers. It marks the point of no return around a black hole.
Stellar evolution: The sequence of physical changes a star undergoes as it consumes nuclear fuel and loses energy. The most massive stars can end their lives by collapsing into black holes.
Karl Schwarzschild: A German physicist whose 1916 solution to Einstein’s field equations describes a spherical, nonrotating vacuum spacetime. His solution supplied the simplest mathematical description of a black hole.
Gravitational-wave astronomy: The study of the universe through gravitational waves generated by accelerating masses. Merging black holes produce signals that reveal their masses, spins, and distances.
Black hole information paradox: The conflict between quantum-mechanical information conservation and the apparent information loss caused by black-hole evaporation. It challenges how Hawking radiation can coexist with quantum theory.
Schwarzschild radius: The horizon radius of a nonrotating, uncharged black hole of a given mass. It relates a black hole’s mass to the size of its event horizon.
Core-collapse supernova: The explosive death of a massive star after its core collapses under gravity. Some stellar collapses leave a black hole rather than a neutron star.
Subrahmanyan Chandrasekhar: An astrophysicist who established the maximum mass of a stable white dwarf, now called the Chandrasekhar limit. His work clarified how stellar remnants can be driven toward further gravitational collapse.
Galaxy formation and evolution: The processes through which galaxies form, change, and acquire their observed structures over cosmic time. Supermassive black holes can influence star formation and gas flows in their host galaxies.
Black hole singularity: A region predicted by classical general relativity where curvature becomes unbounded and the theory ceases to make reliable predictions. Classical black-hole models point toward singularities whose physical nature remains unknown.