Spark image
Black holes

These are bodies with an escape velocity greater than that of light. They swallow up matter - increasing in mass themselves. However if anti matter falls into a black hole then its mass decreases and eventually the black hole fills up and disappears in a burst of radiation.

For a black hole vE = c = [2GM/R]1/2

where vE is the velocity of escape, c the speed of light, G the gravitational constant, M the mass of the star and R its radius.

The diagram represents the gravitational fields outside a large star and then a black hole. The depth of the gravitational vortex is much greater for the black hole than for a heavy star the escape velocity being the speed of light.
Only stars much heavier than the Sun will form black holes. The Sun will become a red giant and then shrink away to a white dwarf and finally a black dwarf.
© Keith Gibbs 2009