Here are the definitions of black holes from NASA (if you are not
interested stop reading now):

Micro-Black Holes

Formation
     Possibly formed in small regions of high density during the first
few seconds of the Big Bang.
Unusual Features
     Micro-black holes aren't so black! Quantum mechanics and
thermodynamics tell us that they should radiate all forms of energy due
to the strongly varying gravitational fields just outside their event
horizon. These black holes slowly radiate themselves away, finally
disappearing in a flash of high-energy radiation.
Size
     If a micro-black hole is created with a mass of greater than 10^17
grams, it would still be around today. This mass corresponds to about a
cubic kilometer of water. In terms of size, it would be smaller than an
electron!
Observations
     Once believed to be a possible source of gamma-ray bursts, there is
no current observational evidence for their existence.

Stellar-Mass Black Holes

Formation
     When a star with a mass of greater than 10 times the mass of the
Sun explodes in a supernova, the central core left behind will collapse
into a black hole.
Unusual Features
     When this type of black hole is part of a binary system, matter can
sometimes stream from the other star into a disk surrounding the black
hole. This is called an accretion disk.
Size
     These black holes would range from about 5 to 100 times the mass of
the Sun, giving them diameters of 20 to 400 miles.
Observations
     At present, there are over 25 objects astronomers suspect may be
black holes near or in our own galaxy. A partial list: Cygnus X-1,
A0620-00, V404 Cygni, LMC X-1, LMC X-3

Super-Massive Black Holes

Formation
     Formed via accretion from smaller bodies in the centers of many
galaxies.
Unusual Features
     On this scale, some of the infalling matter may become redirected
into jets and ejected over the poles of the black holes. This phenomenon
may explain the radio jets observed from the centers of some galaxies.
Size
     HUGE! One million to one billion times the mass of the Sun. They
would be about the size of our solar system.
Observations
     Active Galactic Nuclei (AGN), Seyfert Galaxies, Quasars.

If this is not enough information for you, you can go to the site:

      http://www.geocities.com/Area51/Cavern/6910/high-crusade.html

and page down to the NASA search engine, and enter the words "black
holes" (without quotes).  You will even find articles about the Hubble
telescope's evidence of the existance of black holes.

--
Your humble servant (but hide the good china),

The Privateer <privateer@thevortex.com>
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