Explanation of a Black Hole

There has been lots of bad press about the LHC concerning the possibility of producing "mini black holes that could swallow up the Earth".

Call this post the "anti-Newspaper" if you like.

Ok, so, Black Holes - what are they?

Keeping it simple, here we go.

Stars. Stars are simply large bundles of stuff (mainly hydrogen or protons) that are powered by nuclear reactions, the same kind as in the atom bomb. The reason they do not explode like an atom bomb is that there is so much stuff there, that gravity keeps it all in a ball and contains the millions of atom bombs going off every second.

It is a matter of balance between outward nuclear explosions, and the pressure inwards from the gravity.

That's for a normal star.

However they do not last forever, and there will come a point when there is no hydrogen left to explode. The star shrinks until gravity raises the inside temperature to be hot enough to explode the next element, Helium. When that is finished, it shrinks more, and burns even heavier elements.

Even this can't last forever, and there comes a point when it can no longer make any atom bombs at all.

It gives up at this point, and IMplodes, but the implosion goes right through the centre and what is seen is an EXplosion outwards. We call this a Nova.

What is left is a lot of stuff getting thrown out into space, leaving a small, dense stellar core the size of a small planet. This is called a white dwarf, and will cool into a red, then brown, then black dwarf. Gravity is stopped by outward atomic pressure.

That is for a normal star.

If the star is just a tad bigger to begin with, there is too much stuff in it to make a dwarf star, and the protons add electrons to themselves and all become neutrons, and the star shrinks to a smaller size. Then the IMplosion again, but what is left this time is a Neutron Star, exactly like an atomic nucleus, but the size of a city. Gravity is stopped by outward neutron pressure.

That is for a slightly larger than normal star.

If the star is bigger than about 2.3 times the size of our sun, nothing can stop the shrinking and gravity completely takes over.

To everyone outside, the star is crushed out of existence and becomes a Black Hole.

The size of these black holes depends on the original star, so at 2.3 times bigger than the sun, the black hole would be roughly the size of a football field.

Clearly, most stars are far bigger than the sun, which would mean that their black holes could be as big as a planet. Hovever, this would require a billion billion billion billion tonnes of mass to create.

All due to gravity.

The upshot is that a black hole is formed from compression, of any kind, but we only know about how gravity does it, However, it has been conjectured that during the Big Bang, pressures were so great that the possibility of black hole formation at that time is entirely feasible, bearing in mind that all the stuff of the universe was there at the time to create them.

The fears that the LHC can form mini-black holes are completely groundless because a) the pressure there is about a trillion trillion times less than needed, b) there is simply not enough stuff to make one even if the pressure was available, and c) in order to "swallow the earth" the created black hole would have to be at least as big as the earth.

Ever tried pushing a water melon through the eye of a needle?