Question: can you explain how a black hole works? how does it have the power to destroy everything?!

Ian Cade answered on 17 Nov 2014:

I suppose one way to approach this problem is to understand how black holes are formed:

Stars throughout their lives collapse… or at least their cores do.

As a beginning point you might consider a large cloud of hydrogen, larger than our entire solar system. Some external shock, a nearby star exploding perturbs our gas cloud, causing some bit to be more densely packed. This denser area attracts the rest of the nearby cloud via gravity… and this part of the cloud collapses…

At some point the cloud becomes hot and dense enough for fusion reactions to start. These result in the production of heavier elements and a lot of radiation (light and neutrinos) and this pushes against the cloud of gas and stops it contracting further.

The star will eventually run low on hydrogen and fusion will slow, reducing the radiation pressure that supported the core, which will start to collapse further…

At some point the stellar core will be hot and dense enough to start fusing helium, which releases another burst of radiation to hold the star up and stop it collapsing further.

This process continues through many steps of fusion, running short of fuel and then fusing heavier components. Eventually the stellar core runs out of fuse-able fuel (this happens when it gets to iron, as fusing iron (or heavier) atoms together uses energy). So, the star collapses further…

At some point the collapse is so extreme that to collapse any further would require putting more than two electrons in a particular space (the Fermi exclusion principal says a maximum of two fermion (such as electrons) may occupy any particular space), and it is the electrons pushing back (the ‘electron degeneracy pressure’) that can halt any further collapse… unless the star is big enough and the force of gravity wanting to pull things closer is strong enough. It is possible that the force of gravity can be greater than the electron degeneracy pressure, so the star collapses further.

At some point the electrons and iron nuclei in the core start to fuse, converting all the protons to neutrons. Neutrons are fermions too, so at a particular point they resist being compressed further due to their own ‘neutron degeneracy pressure’. But this is only so strong, and if the star is massive enough and the force of gravity sufficiently extreme this last repulsive force is overcome and the star collapses further…

There is nothing left to stop the collapse, and for all anyone knows, the star collapses to a point of infinite density. And a Black hole is formed. Anything that falls into it gets compressed to a point in the same way as the material that first made the star.

(According to the latest theories) Its not all a one way process though… right at the edge of the black hole, where light travels just fast enough to escape the pull of the black hole, something curious happens… The pairs of tiny particles that pop in and out of existence throughout all space can get separated (one of the pair can be formed closer to the black hole than its twin, and fall in while the twin escapes). From an external observers point of view it looks like the black hole emits a particle and looses a little mass. Indeed eventually all the mass of a black hole could be lost in this way. But for very large black holes this process is very slow