question: How does a gravitational force in/around a black hole work. I understand all that mass squeezed in a small space creates gravity but how can gravity radiate from black holes when even light can't?
comment: Gravity often uses the wave or field model, but it's not a physical thing that that radiates out from the centre of the black hole. Gravity has no mass and isn't affected by gravity. Instead, the existence of the black hole itself (or technically, its mass) creates the gravitational field.
passages: If light were a wave rather than a "corpuscle", it is unclear what, if any, influence gravity would have on escaping light waves. Modern relativity discredits Michell's notion of a light ray shooting directly from the surface of a supermassive star, being slowed down by the star's gravity, stopping, and then free-falling back to the star's surface.
  
  Section::::History.:General relativity.
   It is notable that in general relativity, gravitational radiation, which under the rules of quantum mechanics must be composed of gravitons, is created only in situations where the curvature of spacetime is oscillating, such as is the case with co-orbiting objects. The amount of gravitational radiation emitted by the solar system is far too small to measure.
   The fact that general relativity is modified at large distances in massive gravity provides a possible explanation for the accelerated expansion of the Universe that does not require any dark energy. Massive gravity and its extensions, such as bimetric gravity, can yield cosmological solutions which do in fact display late-time acceleration in agreement with observations.
  
  Observations of gravitational waves have constrained the Compton wavelength of the graviton to be "λ"  , which can be interpreted as a bound on the graviton mass "m"  .
  
  Section::::Linearized massive gravity.
   BULLET::::- Gravitational radiation has been indirectly confirmed through studies of binary pulsars. In 2016, the LIGO experiments directly detected gravitational radiation from two colliding black holes, making this the first direct observation of both the gravitational radiation as well as black holes.
  
  BULLET::::- The expansion of the universe (predicted by the Robertson–Walker metric) was confirmed by Edwin Hubble in 1929.
  
  Section::::Modern era.:Quantum gravity.
   Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force which causes any two bodies to be attracted to each other, with the force proportional to the product of their masses and inversely proportional to the square of the distance between them.
   These properties are special because they are visible from outside a black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law, the ADM mass, far away from the black hole. Likewise, the angular momentum can be measured from far away using frame dragging by the gravitomagnetic field.
   When mass is concentrated into a sufficiently compact region of space, general relativity predicts the formation of a black hole – a region of space with a gravitational effect so strong that not even light can escape. Certain types of black holes are thought to be the final state in the evolution of massive stars. On the other hand, supermassive black holes with the mass of millions or billions of Suns are assumed to reside in the cores of most galaxies, and they play a key role in current models of how galaxies have formed over the past billions of years.
   While light can still escape from the photon sphere, any light that crosses the photon sphere on an inbound trajectory will be captured by the black hole. Hence any light that reaches an outside observer from the photon sphere must have been emitted by objects between the photon sphere and the event horizon.
  
  Section::::Properties and structure.:Ergosphere.
   BULLET::::- Cosmic radiation:
   Timeline of black hole physics
  
  Timeline of black hole physics
  
  Section::::Pre-20th century.
  
  BULLET::::- 1640 — Ismaël Bullialdus suggests an inverse-square gravitational force law
  
  BULLET::::- 1676 — Ole Rømer demonstrates that light has a finite speed
  
  BULLET::::- 1684 — Isaac Newton writes down his inverse-square law of universal gravitation
  
  BULLET::::- 1758 — Rudjer Josip Boscovich develops his theory of forces, where gravity can be repulsive on small distances. So according to him strange classical bodies, such as white holes, can exist, which won't allow other bodies to reach their surfaces
   BULLET::::- 1975 — James Bardeen and Jacobus Petterson show that the swirl of spacetime around a spinning black hole can act as a gyroscope stabilizing the orientation of the accretion disc and jets
  
  BULLET::::- 1989 — Identification of microquasar V404 Cygni as a binary black hole candidate system
  
  BULLET::::- 1994 — Charles Townes and colleagues observe ionized neon gas swirling around the center of our Galaxy at such high velocities that a possible black hole mass at the very center must be approximately equal to that of 3 million suns
  
  Section::::21st century.
   Another way that the black hole nature of an object may be tested in the future is through observation of effects caused by a strong gravitational field in their vicinity. One such effect is gravitational lensing: The deformation of spacetime around a massive object causes light rays to be deflected much as light passing through an optic lens. Observations have been made of weak gravitational lensing, in which light rays are deflected by only a few arcseconds. However, it has never been directly observed for a black hole. One possibility for observing gravitational lensing by a black hole would be to observe stars in orbit around the black hole. There are several candidates for such an observation in orbit around Sagittarius A*.
   The very strong gravitational fields that are present close to black holes, especially those supermassive black holes which are thought to power active galactic nuclei and the more active quasars, belong to a field of intense active research. Observations of these quasars and active galactic nuclei are difficult, and interpretation of the observations is heavily dependent upon astrophysical models other than general relativity or competing fundamental theories of gravitation, but they are qualitatively consistent with the black hole concept as modeled in general relativity.
  
  Section::::Strong field tests.:Binary pulsars.
   BULLET::::- The time delay of light passing close to a massive object was first identified by Irwin I. Shapiro in 1964 in interplanetary spacecraft signals.
  
  BULLET::::- Gravitational radiation has been indirectly confirmed through studies of binary pulsars. On 11 February 2016, the LIGO and Virgo collaborations announced the first observation of a gravitational wave.
   BULLET::::- 1784 — John Michell discusses classical bodies which have escape velocities greater than the speed of light
  
  BULLET::::- 1795 — Pierre Laplace discusses classical bodies which have escape velocities greater than the speed of light
  
  BULLET::::- 1798 — Henry Cavendish measures the gravitational constant "G"
  
  BULLET::::- 1876 — William Kingdon Clifford suggests that the motion of matter may be due to changes in the geometry of space
  
  Section::::20th century.
  
  BULLET::::- 1909 — Albert Einstein, together with Marcel Grossmann, starts to develop a theory which would bind metric tensor "g", which defines a space geometry, with a source of gravity, that is with mass
   When one talks about the surface gravity of a black hole, one is defining a notion that behaves analogously to the Newtonian surface gravity, but is not the same thing. In fact, the surface gravity of a general black hole is not well defined. However, one can define the surface gravity for a black hole whose event horizon is a Killing horizon.
   Section::::Why gravity is weak and the cosmological constant is small.
   BULLET::::- The theory's prediction of frame dragging was consistent with the recent Gravity Probe B results.
  
  BULLET::::- General relativity predicts that light should lose its energy when traveling away from massive bodies through gravitational redshift. This was verified on earth and in the solar system around 1960.
  
  Section::::History of gravitational theory.:Gravity and quantum mechanics.
   Section::::Theory.
  
  It is hypothesized that gravitational interactions are mediated by an as yet undiscovered elementary particle, dubbed the "graviton". The three other known forces of nature are mediated by elementary particles: electromagnetism by the photon, the strong interaction by gluons, and the weak interaction by the W and Z bosons. All three of these forces appear to be accurately described by the standard model of particle physics. In the classical limit, a successful theory of gravitons would reduce to general relativity, which itself reduces to Newton's law of gravitation in the weak-field limit.
   General relativity plays a central role in modelling all these phenomena, and observations provide strong evidence for the existence of black holes with the properties predicted by the theory.
   Section::::Geometry and gravitation.:Sources of gravity.
  
  In Newton's description of gravity, the gravitational force is caused by matter. More precisely, it is caused by a specific property of material objects: their mass. In Einstein's theory and related theories of gravitation, curvature at every point in spacetime is also caused by whatever matter is present. Here, too, mass is a key property in determining the gravitational influence of matter. But in a relativistic theory of gravity, mass cannot be the only source of gravity. Relativity links mass with energy, and energy with momentum.
   Based on observational evidence, it is now known that gravity interacts with all forms of energy, and not just with mass. The electrostatic binding energy of the nucleus, the energy of weak interactions in the nucleus, and the kinetic energy of electrons in atoms, all contribute to the gravitational mass of an atom, as has been confirmed to high precision in Eötvös type experiments.
  
  Section::::Non-gravitational applications and analogies.
  
  BULLET::::- Mock gravity:
   The second definition is the radius at which the enclosed mass in stars equals twice M, i.e.
  
  formula_2.
  
  Which definition is most appropriate depends on the physical question that is being addressed. The first definition takes into account the bulge's overall effect on the motion of a star, since formula_3 is determined in part by stars that have moved far from the black hole. The second definition compares the force from the black hole to the local force from the stars.
   BULLET::::- The Reissner–Nordström solution, in which the central object has an electrical charge. For charges with a geometrized length which are less than the geometrized length of the mass of the object, this solution produces black holes with an event horizon surrounding a Cauchy horizon.
  
  BULLET::::- The Kerr solution for rotating massive objects. This solution also produces black holes with multiple horizons.
  
  BULLET::::- The cosmological Robertson–Walker solution, which predicts the expansion of the universe.
   BULLET::::- Black holes have the same gravitational effects as any other equal mass in their place. They will draw objects nearby towards them, just as any other planetary body does, except at very close distances to the black hole. If, for example, the Sun were replaced by a black hole of equal mass, the orbits of the planets would be essentially unaffected. A black hole "can" act like a "cosmic vacuum cleaner" and pull a substantial inflow of matter, but only if the star from which it formed was already having a similar effect on surrounding matter.
  
presuppositions: Gravity radiates from black holes.
corrections: Gravity uses a wave or field model, but it doesn't physically radiate from the center of a black hole.
raw_presuppositions: Gravity radiates from black holes. Gravity radiates from black holes.
raw_corrections: Gravity uses a wave or field model, but it doesn't physically radiate from the center of a black hole. The black hole itself creates a gravitational field.