The following outline is provided as an overview of and topical guide to black holes:
Black hole – mathematically defined region of spacetime exhibiting such a strong gravitational pull that no particle or electromagnetic radiation can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features. In many ways a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.
What type of thing is a black hole?
A black hole can be described as all of the following:
Schwarzschild metric – In Einstein's theory of general relativity, the Schwarzschild solution, named after Karl Schwarzschild, describes the gravitational field outside a spherical, uncharged, non-rotating mass such as a star, planet, or black hole.
Virtual black hole – black hole that exists temporarily as a result of a quantum fluctuation of spacetime.
Types of black holes, by size
Micro black hole – predicted as tiny black holes, also called quantum mechanical black holes or mini black holes, for which quantum mechanical effects play an important role.
Extremal black hole – black hole with the minimal possible mass that can be compatible with a given charge and angular momentum.
Black hole electron – if there were a black hole with the same mass and charge as an electron, it would share many of the properties of the electron including the magnetic moment and Compton wavelength.
Stellar black hole – black hole formed by the gravitational collapse of a massive star. They have masses ranging from about 3 to several tens of solar masses.
Intermediate-mass black hole – black hole whose mass is significantly more than stellar black holes yet far less than supermassive black holes .
Supermassive black hole – largest type of black hole in a galaxy, on the order of hundreds of thousands to billions of solar masses.
Quasar – very energetic and distant active galactic nucleus.
Active galactic nucleus – compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum.
Blazar – very compact quasar associated with a presumed supermassive black hole at the center of an active, giant elliptical galaxy.
Specific black holes
List of black holes – incomplete list of black holes organized by size; some items in this list are galaxies or star clusters that are believed to be organized around a black hole.
White dwarf – also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter.
Supernova – stellar explosion that is more energetic than a nova.
Hypernova – also known as a Type Ic Supernova, refers to an immensely large star that collapses at the end of its lifespan.
Gamma-ray burst – flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies.
Properties of black holes
Accretion disk – structure (often a circumstellar disk) formed by diffused material in orbital motion around a massive central body, typically a star. Accretion disks of black holes radiate in the X-ray part of the spectrum.
Black hole thermodynamics – area of study that seeks to reconcile the laws of thermodynamics with the existence of black hole event horizons.
Schwarzschild radius – distance from the center of an object such that, if all the mass of the object were compressed within that sphere, the escape speed from the surface would equal the speed of light.
M–sigma relation – empirical correlation between the stellar velocity dispersion of a galaxy bulge and the mass M of the supermassive black hole at
Event horizon – boundary in spacetime beyond which events cannot affect an outside observer.
Subrahmanyan Chandrasekhar – in 1931, using special relativity, postulated that a non-rotating body of electron-degenerate matter above a certain limiting mass (now called the Chandrasekhar limit at 1.4 solar masses) has no stable solutions.
Roy Kerr – In 1963, found the exact solution for a rotating black hole
Models of black holes
Gravitational singularity – or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system.
Primordial black hole – hypothetical type of black hole that is formed not by the gravitational collapse of a large star but by the extreme density of matter present during the universe's early expansion.
Gravastar – object hypothesized in astrophysics as an alternative to the black hole theory by Pawel Mazur and Emil Mottola.
Dark star (Newtonian mechanics) – theoretical object compatible with Newtonian mechanics that, due to its large mass, has a surface escape velocity that equals or exceeds the speed of light.
Ring singularity – describes the altering gravitational singularity of a rotating black hole, or a Kerr black hole, so that the gravitational singularity becomes shaped like a ring.
Immirzi parameter – numerical coefficient appearing in loop quantum gravity, a nonperturbative theory of quantum gravity.
Membrane paradigm – useful "toy model" method or "engineering approach" for visualising and calculating the effects predicted by quantum mechanics for the exterior physics of black holes, without using quantum-mechanical principles or calculations.
Kugelblitz (astrophysics) – concentration of light so intense that it forms an event horizon and becomes self-trapped: according to general relativity, if enough radiation is aimed into a region, the concentration of energy can warp spacetime enough for the region to become a black hole .
Wormhole – hypothetical topological feature of spacetime that would be, fundamentally, a "shortcut" through spacetime.
Quasi-star – hypothetical type of extremely massive star that may have existed very early in the history of the Universe.
No-hair theorem – postulates that all black hole solutions of the Einstein-Maxwell equations of gravitation and electromagnetism in general relativity can be completely characterized by only three externally observable classical parameters: mass, electric charge, and angular momentum.
Nonsingular black hole models – mathematical theory of black holes that avoids certain theoretical problems with the standard black hole model, including information loss and the unobservable nature of the black hole event horizon.
Holographic principle – property of quantum gravity and string theories which states that the description of a volume of space can be thought of as encoded on a boundary to the region—preferably a light-like boundary like a gravitational horizon.
Black hole complementarity – conjectured solution to the black hole information paradox, proposed by Leonard Susskind and Gerard 't Hooft.
Black hole metrics
Schwarzschild metric – describes the gravitational field outside a spherical, uncharged, non-rotating mass such as a star, planet, or black hole.
Kerr metric – describes the geometry of empty spacetime around an uncharged, rotating black hole (axially symmetric with an event horizon which is topologically a sphere)
Reissner–Nordström metric – static solution to the Einstein-Maxwell field equations, which corresponds to the gravitational field of a charged, non-rotating, spherically symmetric body of mass M.
Kerr-Newman metric – solution of the Einstein–Maxwell equations in general relativity, describing the spacetime geometry in the region surrounding a charged, rotating mass.
Astronomical objects including a black hole
Hypercompact stellar system – dense cluster of stars around a supermassive black hole that has been ejected from the centre of its host galaxy.
^Hughes, Scott A. (2005). "Trust but verify: The case for astrophysical black holes". arXiv:hep-ph/0511217.
^A Brief History of Time, Stephen Hawking, Bantam Books, 1988.
Michell, J. (1784). "On the Means of Discovering the Distance, Magnitude, &c. of the Fixed Stars, in Consequence of the Diminution of the Velocity of Their Light, in Case Such a Diminution Should be Found to Take Place in any of Them, and Such Other Data Should be Procured from Observations, as Would be Farther Necessary for That Purpose". Philosophical Transactions of the Royal Society. 74: 35–57. Bibcode:1784RSPT...74...35M. doi:10.1098/rstl.1784.0008. JSTOR 106576.
^Gillispie, C. C. (2000). Pierre-Simon Laplace, 1749-1827: a life in exact science. Princeton paperbacks. Princeton University Press. p. 175. ISBN 978-0-691-05027-0.
Israel, W. (1989). "Dark stars: the evolution of an idea". In Hawking, S. W.; Israel, W. (eds.). 300 Years of Gravitation. Cambridge University Press. ISBN 978-0-521-37976-2.
Schwarzschild, K. (1916). "Über das Gravitationsfeld eines Massenpunktes nach der Einsteinschen Theorie". Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften (in German). 7: 189–196. Bibcode:1916SPAW.......189S. Schwarzschild, K. (1916). "Über das Gravitationsfeld eines Kugel aus inkompressibler Flüssigkeit nach der Einsteinschen Theorie". Sitzungsberichte der Königlich Preussischen Akademie der Wissenschaften (in German). 18: 424–434. Bibcode:1916skpa.conf..424S.
^'t Hooft, G. (1985). "On the quantum structure of a black hole". Nuclear Physics B. 256: 727–745. Bibcode:1985NuPhB.256..727T. doi:10.1016/0550-3213(85)90418-3. 't Hooft, G. (1990). "The black hole interpretation of string theory". Nuclear Physics B. 335 (1): 138–154. Bibcode:1990NuPhB.335..138T. doi:10.1016/0550-3213(90)90174-C.