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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
http://www.space.com/15421-black-holesfacts-formation-discovery-sdcmp.html
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.
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
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)
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.
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.
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
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.
Interesting facts!
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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.
http://www.youtube.com/watch?v=eI9CvipHl
_c&feature=related
http://www.youtube.com/watch?v=p2zhaoyM
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