1. Black Holes: Facts, Theory, and Definition
An artist's drawing a black hole named Cygnus X-1. It formed when a large star caved in. This black hole pulls matter from blue star beside it.
Image Credit: 
NASA/CXC/M.Weiss

3. What is a Black Hole?
VERY dense place in space where gravity has become so extreme that it overwhelms all other forces.
Gravity is so strong because matter has been squeezed into a tiny space.
Because no light can escape, we can't see black holes.
But…we can see how stars and gas that are very close act differently than other stars.
When a star and black hole are close together, high energy light is made and can be measured by satellites/telescopes.
May pull gas off the star and create an “accretion disk” around itself.

6. Discovery
First predicted by Einstein in 1916 with the general theory of relativity.
Term “black hole” was coined in 1967 by John Wheeler, American astronomer.
First discovered by Wheeler in 1971

7. Type: Primordial Smallest
Scientists think they may be the size of a single atom but have the mass of a mountain
Thought to have formed early (right after the Big Bang)

8. Type: Stellar Formed when a massive star collapses
Relatively small, but VERY dense
Mass may be up to 20x more than the mass of our Sun
Consume dust and gas around them to grown in size.

9. Type: Supermassive
May be millions or billions of times the mass of the Sun but have the same radius
Thought to be at the center of every galaxy
Sagittarius A is the center of Milky Way.
Scientists aren’t sure how they form, may be the result of:
many smaller black holes merging
large gas clouds collapsing and accreting mass
collapse of a group of stars
Once formed, they gather gas and dust from around them and grow.

10. Black Hole Theory Incredibly massive but only cover a small area.
Extremely strong gravitational force – not even light can escape
Holes have 3 “layers”
Outer event horizon
Inner event horizon
Singularity

11. The layers…
Event horizon - boundary around the mouth of the black hole where light loses its ability to escape
Once a particle crosses the event horizon, it cannot leave.
Singularity
Single point in space-time where the mass of the black hole is concentrated.

12. Interesting facts!
If you fell into a black hole, gravity would stretch you out like spaghetti. Don't worry; your death would come before you reached singularity.
Black holes do not "suck." Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them.
The first object considered to be a black hole is Cygnus X-1. Rockets carrying Geiger counters discovered eight new x-ray sources. In 1971, scientists detected radio emission coming from Cygnus X-1, and a massive hidden companion was found and identified as a black hole.
Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and a fellow physicist Kip Thorne, with Hawking betting that the source was not a black hole. In 1990, he conceded defeat. [VIDEO: Final Nail in Stephen Hawking's Cygnus X-1 Bet?]
Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun.
If a star passes too close to a black hole, it can be torn apart.
Astronomers estimate there are anywhere from 10 million to a billion stellar black holes, with masses roughly thrice that of the sun, in the Milky Way.
The interesting relationship between string theory and black holes gives rise to more types of massive giants than found under conventional classical mechanics.