A black hole is a region of ignorance-it is beyond the knowledge of human physicists who have inferred the observable effects into consistence with Einstein's theories. No one knows for certain what goes on beyond the event horizon though it seemslogically plain-except for the singularity and the reality of what's beyond.
The cause of a black hole of course differs from a description of what it is. Black holes may be caused by the issue of a universe to start with. Space-time, dimensions and energy all seem to have issued together from an initial singularity. If it is a scalar field then the structural changes it has were pre-determined in the beginnings such that the actualization of the temporal process fulfills the initial form. With space-time concentrated by gravity a parallel of the concentration of mass and energy in to shells of protocols bound by forces exists. intervals and reference frames in the temporal universe are a reduction from an eternal, possibly unextended initial condition of perfection without need for the more limited dimensions and temporal progression of space time.It would be an ironic turn if black holes served some sort of larger purpose in balancing the 11 dimensional hidden universe and it's deployment of an underlying if not inverse space-time field in order that temporality might be created consistent with the mass of the Universe of four dimensions. Einsteins space-time frame of reference criteria seems to have an analogue in the concentration of mass and energy in to naked singularities (those without an event horizon). One can readily imagine a zero dimensional membrane or pure idea of the spirit of incredible comparative power releasing a structure of being that appears as matter and energy to those existing within it's parameters. Black holes as minor singularities or infinities contained in space-time warps may transcend normal force and become zero-dimensional, infinite yet bounded points themselves. Such phenomena could wrap up aspects of gravity and provide the 'dark energy' allowing the Universe to accelerate faster by changing the structure of space-time enabling the remaining matter to move away without as significant of inhibition.
Some of that energy that became mass would draw together because of gravitational attraction with such density that in theory light could not escape the gravity, and neither could anything else. The quantum entanglement of wave-particles in black holes isn't plain to me , and neither are the roles of extra dimensions of M-Theory in a black hole. If there was a singularity and all of the matter was condensed below the plank length at some point then some of the mass should possible go in to the other dimensions of super-string or M-Theory. The nature of those extra dimensions and their relationship to space-time could or could not be malleable. Newton thought an absolute space and time existed while Einstein did not as his relativity theories indicate. Could dimensions of the sub-plank length size have some constant scale in one direction regarding maximum size (less than our four dimensions of normal space-time), but no minimum size? What happens to energy that is condensed below the plank length in other dimensions-is the energy neutralized by the annihilation of matter and anti-matter (to a high percent of the total mass at time zero) in the other smaller dimensions or elsewhere? Is the energy prevented by some scaler field limit or other boundary condition from entering the evident Universe of normal space-time. Such questions can arise from contemplation of the mystery of black holes. So back to basics...
When gravity warps space time sufficiently because of concentrated mass nothing at all (except for some leaking virtual particles) can overcome the 'black' hole of the gravitational field from within to escape without-anything that could be considered as mass or energy hasn't got the power or speed to go faster than light or through the walls of curved gravity of a concentrated space-timer event called a black hole sufficiently to buy a Pastrami sandwich in Cleveland.
Everyone knows that the Heisenberg Uncertainty Principle means that all particles have a non locality-perhaps in a sufficiently dense gravitational field such as a black hole matter is forced through a dimensional scuppers to other locations and only a facade of a curved space event horizon remains with the strength of the field maintained through relationship with the other dimensions. Some speculate that gravity has extra dimensional existence such that it increases in short distances at the cube root of the distance instead of the square root-that would affect black holes too and gorge the extra subversive dimensions obviously.
The Schwarzschild radius aka. gravitational radius was discovered in 1916 by Karl Schwarzschild. A given radius of any mass object can be determined such that below that size it will collapse into a gravitational singularity. 1 / (2M r)
The Wikipedia article above notes that the size for the sun is three kilometers, and for the earth it is 9 centimeters (approximately the size of the financial I.Q. of the U.S. Congress). Black holes form when mass exceeds a given size in a volume smaller than the Schwarzschild radius. Baby black holes may form of a financial and intellectual deficit nature when crooked politicians have sufficient power (just thought I'd lighten up to post).
The cause of a black hole's existence is simple enough nominally-a star of sufficient mass burns up its fuel and loses enough energy to keep the dead' weight from collapsing inward. The mass of the inwardly collapsing star overcomes and annihilates the atomic forces of the atoms. Space-time warps and not even light quanta escape the intense gravitational field. The star becomes a lurch living in a black hole from which nothing escapes. At least that was the basic parameter before Stephen Hawking Gerard D'Hooft, Jacob Bekenstein and others formulated laws regarding black hole thermodynamics reconciling entropy, surface temperature and surface area (event horizon). The zeroth law is such that a body in thermal equilibrium has a constant temperature. Obviously the Universe itself isn't in thermal equilibrium, and one wonders if space-time has a temperature beyond the background radiation for itself.
Black holes exist as an aspect of the existence of space-time. The particular proximal causality may not be the same as the actual 'cause'. A cause tends to refer to preceding events or necessary conditions for a certain circumstance or phenomena to happen. One might therefore say that in the largest or most basic sense that the Universe is the cause of a black hole or black holes. In the very young Universe small black holes may have formed when mass density was higher. I haven't any idea how that phenomenon would be affected by the Chandrasekhar limit which limits how much mass can stay together formed with electron-degeneracy pressure.
Singularities are of two or three sorts, and they are the main point of interest perhaps regarding elements of black holes. They have different origins and functions, and stories of their own. Curvature singularities and conical singularities are two primary sorts of space-time singularity. Naked singularities are those without an event horizon. Non-rotating black holes have different structure than rotating ones. A diffeomorphism invariant math test for the singularity may find that it continues to exist in other scalar field contexts rather than being a sort of unsolved infinity of a math theory...I believe this means that the singularity has a better chance of existing in fact.
http://en.wikipedia.org/wiki/Gravitational_singularity 0-dimensional singularity:
1-dimensional singularity: cosmic string
2-dimensional singularity: domain wall
Black holes may cause the angular momentum of galaxies indirectly and some conjecture that the universe began in a black hole and will end in another after a big crunch if enough missing mass exists to let the gravity of the Universe slow the expansion one day and bring it to a compaction and total collapse. Investment bankers and the past two administrations have worked on an analogous project called 'globalism'.
It has been written that mathematical preferences regarding system determine what one believes about the Universe and its cosmological history and existence. M-theory and super-string theories for instance have quite incomplete mathematical development so far, and therefore cannot completely correspond to a complete cosmological theory. Black holes while having an apparent existence with observable influence upon other astronomical bodies are nevertheless largely unknown outside of logical inference regarding their composition and etiology.
At the most basic level gravity is thought to be the proximal cause of a black hole. The mass of a black hole becomes so dense that no mass can escape its gravitational field. Because the interior of a black hole is entirely conjectural so far, and the math work also incomplete the structure of a black hole and its gravitational compaction of mass to a near zero-size point produce infinities that do not provide a plain resolution for understanding. One of the reasons for incomplete math modeling of the Universe and of black holes is the failure of development of a unified field theory. Einstein worked upon a unified field theory for the remainder of his career after completion of the general and special theories of relativity without success, yet at least he did examine the difficulty in uniting the mathematical foundations of the macro-cosmic with the micro-cosmic world of quantum mechanics. Quantum cosmology or a unification of large scale with local sub-atomic structures to such a degree of accuracy that the interiors of black holes might accurately be understood as well as the metaphysical pre-existing structure of the non-observable universe before time=0 and after time omega is an actual point that physicists consider.
Time and space are united together in relativity theory. There is no universal, pervasive space-time within the universe, although plainly common sense indicates that the universe itself has a space-time history that could at least be considered as phases or days. Day one might have been the inflaton from a Higgs field with the weight of the universe less than 20 pounds. Day two could have been the time a fraction of a second later when matter won a slight existence over anti-matter because of a symmetry violation. With the expansion of space-time and dispersion of the initial matter and dimension to more normal, larger forms stars eventually were able to form within a hundred million years by condensing matter with gravity. Phase one stars lasted just a few million years, supernova'd yield heavy metals and Phase two stars with long life were able to form as the Universe continued to expand. Black holes may not have formed until the end of the second generation of stars when the stellar cycles permitted enough mass to exist with fusion being produced or fission which would have tended to eject stellar material aggregated with gravity.
What gravity is, is the essential question about black holes, where they came from, what they are and what their relation is to the rest of space time. There are at least two approaches to space-time theory generally; one regards space-time as a continuum of unified actual field while the other considers it a pointillist' composition of discrete parts. The two approaches are radically different with far different consequences including those for what black holes actually are.
In standard cosmological models the math is incomplete and models are used with dead reckoning' corrections that are use-truths' to help in understanding what is. In some of the other theories the universe may have many extra dimensions, and gravity too may exist in an extra dimensions with increased strength at possible measurable yet small distances equal to the size of the smaller dimension it exist in outside of the standard three. The relationship of strings, (mem) branes or monads that support the apparent existence of larger packets of mass units such as quarks may determine in part what a black hole is and how it grounds it's mass to the underlying known and unknown dimensions of space-time. It is possible that the dark energy or missing mass of the Universe may have some sort of a relationship to the interior configuration of black holes in that mass could be acting upon the standard three dimensions as a sort of attachment upon them pulling the universe inside out' in a way that it seems to be accelerating outward at an increasing pace towards a big rip'. Some speculate that the Universe may rip apart its space time through increasing expansion speed in a relatively brief time universally speaking.
The Heisenberg uncertainty principal brought to light the non-locality of quantum particles ultimately. Non-locality resides implicitly in every quantum particle or super-strings that comprise it. More so than the takeover of the United States by adverse Mexican illegal aliens the pervasive substructure of the Universe has a mysterious and vast nature that wells up in to the phenomena of black holes too.
The center of the Milky Way Galaxy and perhaps that of every galaxy has a large black hole around which the other millions of stars spin as they too spiral toward their ultimate doom perhaps even before they burn up their stellar fuels for fission and fusion. The gigantic black holes may have already consumed thousands of stars as they warp space-time more tightly or radically about themselves. At least that is the basis for understanding within relativity theory, and that could eventually be transcended. Super massive black holes at the center of galaxies may have been formed by accretions of stellar material or interstellar nebulae/dust clouds, from formation of vast relativistic stars or originally in the highly dense early Universe.
Some consider that accretion disks around black holes may be the last remaining visible light parts of the Universe as it dwindles to a low power stage without known alternate energy.