Dividing by zero
No not anything divided by 0 will be infinity. Technically, you cannot divide by 0.
The infinity comes from the limit of a/x where x >= 0.
lim a/x = +inf
x>=0
lim a/x = -inf
x<=0
And this is exactly what happens with Einsteins relativistic correction factor (if I translated it correctly).
According to his formula, to achieve lightspeed, you would need an infinite amount of energy to "reach" lightspeed itself.
Dividing by 0 can also pretty much be illustrated with the equation:
a/0 = b
<=> a = b*0
consequently, this equation only isn't false when a = 0.
And then still, b could be any real number, the equation still wouldn't be false.
That's why 0/0 is called "undefined".
Black holes
Now the black holes.
Black holes are discovered indirectly by observing the effects on gas or stars affected by them.
This is also the case for the radiation and heat. The heat and radiation doesn't come from the black hole itself, but from the gas orbitting around the black hole. The friction between the gas atoms becomes so huge of their speed, that it's being converted to this radiation and heat.
Then we come to the mass and density matter.
People often think that black holes have infinite mass and gravitation. But this is not what it is. What a black hole DOES have is infinite density.
density = mass/volume
the mass stays the same, andthus the gravitational pull also stays the same as before.
The one thing that differs from before is the volume. A black hole has a volume of a mathematical point. Because of that, mass/0 would be infinity (check the limits I described above).
Gravitation:
Because the volume difference, things are able to get closer to a black hole. Gravitation is calculated from the distance between the 2 centers of the masses.
gravity = (G*m1*m2)/r^2
Because the center of the mass is actually the same as the volume, you can get practically as close as you want to the black hole as you want. And maybe you saw this coming already, you get again a 0 for r, which leaves us again with a/0.
This means: gravity is infinite when you are at a distance of 0 to the black hole.
I hope this explains a little
It's the programmer's life:
Have a problem, solve the problem, and have a new problem to solve.