how does a black hole form?

Black holes are thought to form during the course of stellar evolution. As nuclear fuels are exhausted in the core of a star, the pressure associated with their energy production is no longer available to resist contraction of the core to ever-higher densities. Two new types of pressure, electron and neutron pressure, arise at densities a million and a million billion times that of water, respectively, and a compact white dwarf or a neutron star may form. If the star is more than about five times as massive as the Sun, however, neither electron nor neutron pressure is sufficient to prevent collapse to a black hole.

If a black hole could exist it would follow a series of events initiated by a super-nova explosion.

A 20 solar mass star, after exploding would leave a remnant that would be about 2 to 3 solar masses and a diameter of about 100 km,a white dwarf.

If the white dwarf accreted any matter,it's gravity would cause it collapse into a neutron star.

This 2 to 3 solar mass entity would have a diameter of between 16 and 20 km.

If the neutron star gained some mass,such that it's structure could not maintain it's diameter it would collapse to about 3 km diameter..

The surface gravity would be such that the surface escape velocity would be greater than the speed of light and it would become invisible.

Black holes are strictly theoretical entities and there are some compelling reasons why they cannot exist.

In stars, size does matter.

For stars that are around the mass of our sun (or less), when they die they become white dwarf stars. They aren't masive enough to be more than that.

For stars more massive than about 1.5 times our sun when they die, they become neutron stars - the extra mass means that when they collapse its with a bigger whomp and the matter is crushed into itself (the electrons end up combining with the protons in the atoms, and that creates neutrons).

For stars that are more massive than about 8 times our sun when they die, they are so massive that nothing can stop the gravitational WHOMP when it collapses - there isn't enough heat in the center anymore (since all the fuel is gone) that nothing can hold up all that mass.

Those become black holes whether they explode as supernovas first and then collapse, or just collapse.

So black holes don't form from nothing (not sure where you got that).

They form from the most massive stars that exist.

There is a lot more science behind all this - the April 2007 issue of "Astronomy" magazine has a very good article on black holes. Or if you want to get into some heavy science on this, the June 12 2007 issue of "Scientific American Reports" magazine is devoted to black holes.

When a star runs out of fuel, what happens next is determined by how massive the star was. A star like our sun will go into a red giant phase, and the outer layers will blow off into space -- the small glowing core left behind is a white dwarf. Really massive stars can explode completely when they run out of nuclear fuel; this is a supernova. After that happens, the core can contract under gravity into an incredibly dense ball of neutronium (a neutron star). If there is enough matter left over after the explosion, even the neutron star can keep contracting until it becomes something so small and dense that its gravitational pull won't even allow light to escape.... this is a black hole.

First, black holes form from dying stars, not from nothing. When a massive star loses enough fuel to sustain the pressure to counter gravity (via fusion), it will collapse. At this point,the gravity is a function of the star's mass and the distance between the atoms. As, so as it collapses, the gravity increases to (near) infinity.

As for the white dwarf black hole (and red giant), these are dead stars that depend one mass. Neutron stars are just super massive, super dense stars.

A black hole is a region of space in which the gravitational field is so powerful that nothing can escape after having fallen past the event horizon. The name comes from the fact that even electromagnetic radiation (e.g. light) is unable to escape, rendering the interior invisible. However, black holes can be detected if they interact with matter outside the event horizon, for example by drawing in gas from an orbiting star. The gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation in the process.

While the idea of an object with gravity strong enough to prevent light from escaping was proposed in the 18th century, black holes as presently understood are described by Einstein's theory of general relativity, developed in 1916. This theory predicts that when a large enough amount of mass is present within a sufficiently small region of space, all paths through space are warped inwards towards the center of the volume, forcing all matter and radiation to fall inward

depending on size of star and magnitude also time difference of age determines how that star will end up

A black hollow is basically an excellent call that has collapsed in what's stated as a supernova. while an excellent call "is going" supernova, it rather is inner gravity is so great that the outer areas of the super call fall down inward, then rebound in a sizable explosion. This explosion supplies us each and all the climate previous Beryllium. Now, after this explosion, a number of those supernovas form black holes. A black hollow, in case you need to work out it (it rather is rather invisible) is a sphere. the form horizon is a community around the black hollow the place each thing is going in, yet no longer something is going out (the factor of no return). A black hollow is defined as singularity. this is basically infinitely small, and infinitely dense. What is going on interior a black hollow? no person knows. by way of the way, you stated that a black hollow types while an excellent call burns out, yet as I stated until eventually now, the black hollow is a results of a gravitational fall down, no longer an excellent call burning out.

You first need to know what a black hole is...

A black hole is a region of space in which the gravitational field is so powerful that nothing can escape after having fallen past the event horizon. The name comes from the fact that even electromagnetic radiation is unable to escape, rendering the interior invisible. However, black holes can be detected if they interact with matter outside the event horizon, for example by drawing in gas from an orbiting star. The gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation in the process.

now...

Stars undergo gravitational collapse when they can no longer resist the pressure of their own gravity. This usually occurs either because a star has too little "fuel" left to maintain its temperature, or because a star which would have been stable receives a lot of extra matter in a way which does not raise its core temperature. In either case the star's temperature is no longer high enough to prevent it from collapsing under its own weight.

The collapse transforms the matter in the star's core into a denser state which forms one of the types of compact star. Which type of compact star is formed depends on the mass of the remnant, i.e. of the matter left to be compressed after the supernova triggered by the collapse has blown away the outer layers.

Only the largest remnants, those exceeding 1.4 solar masses (known as the Chandrasekhar limit), generate enough pressure to produce black holes, because singularities are the most radically transformed state of matter known to physics (if you can still call it matter) and the force which resists this level of compression, neutron degeneracy pressure, is extremely strong. Remnants exceeding 5 solar masses are produced by stars which were over 20 solar masses before the collapse.

In stars which are too large to form white dwarfs, the collapse releases energy which usually produces a supernova, blowing the star's outer layers into space so that they form a spectacular nebula. But the supernova is a side-effect and does not directly contribute to producing a compact star. For example a few gamma ray bursts were expected to be followed by evidence of supernovae but this evidence did not appear, and one explanation is that some very large stars can form black holes fast enough to swallow the whole star before the supernova blast can reach the surface.

and...

White dwarfs are thought to represent the end point of stellar evolution for main-sequence stars with masses from about 0.07 to 10 solar masses. The composition of the white dwarf produced will differ depending on the initial mass of the star.

If the mass of a main-sequence star is lower than approximately half a solar mass, it will never become hot enough to fuse helium at its core.

If the mass of a main-sequence star is between approximately 0.5 and 8 solar masses, its core will become sufficiently hot to fuse helium into carbon and oxygen via the triple-alpha process, but it will never become sufficiently hot to fuse carbon into neon. Near the end of the period in which it undergoes fusion reactions, such a star will have a carbon-oxygen core which does not undergo fusion reactions, surrounded by an inner helium-burning shell and an outer hydrogen-burning shell.

If a star is sufficiently massive, its core will eventually become sufficiently hot to fuse carbon to neon, and then to fuse neon to iron. Such a star will not become a white dwarf as the mass of its central, non-fusing, core, supported by electron degeneracy pressure, will eventually exceed the largest possible mass supportable by degeneracy pressure. At this point the core of the star will collapse and it will explode in a core-collapse supernova which will leave behind a remnant neutron star or a black hole.

I can only answer the first question.

A black hole forms from a star that gets too big and then implodes on itself.

Science is a lie. God makes everything happen. God just has to think it, and it shall happen. Praise Allah.