well, there are two ways to look at this.

First:

any body of matter has a mass, and therefore gravity. The amount of gravity varies with the given mass of a body. There is a certain escape velocity that varies with a given gravitational pull. Thus, like the earth, there is an escape velocity that an escaping body needs to attain to escape the gravitational force that holds that particular body "on earth".

Now given the above example, take a star with a given mass, that has collapsed to the point that its density has greatly increased, but its mass stayed the same. i.e. its ratio of mass per surface area has increased exponentially. As this dying star keeps collapsing, its escape velocity increases to the point at which it approaches the velocity of c; too which eventually not even light can escape, due to the approaching infinite density (singularity).

Second:

The second understanding requires a bit of understanding with relativity. But if you understand the basics, you'll get it.

As the star's surface collapses and its density increases, relativistic effects also take place. This however would not be noticeable too much only untill the collapsing star approached the critical mass radius. (Schwartzchild radius) What happens is time dilation. (time slows down from an outside FOR, frame of reference, looking in towards the star) Because the time dilates, the light (photons) emitted from the dying star begin to exponentially become spaced further and further apart. Thus from an outside FOR, the observer would observe the light emitted becoming more and more dim and red-shifted. This would continue to happen untill the star got so exponentially close to the event horizon that, for all practical purposes, the star would appear to disappear. (due to the conservation of energy law)

make sense now?

-nåte

• yes, thanks (nt) - Barry - August 21, 1999 - 16:05 UTC
  • Re: yes, thanks (nt) - richard_david/">richard david - August 23, 1999 - 12:46 UTC