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animation of blackhole
animation of blackhole
History of Black Holes

What is a black hole? Black holes are very dense and massive. They exert so large of a gravitational force that nothing, not even light, can escape their pull. It is a hole because nothing can ever come out. Since not even light or other electromagnetic radiation can escape, it is called a black hole. In a black hole, gravity has become so extreme that it overwhelms all other forces in the universe. 1

check out this cool video of a black hole! http://imagine.gsfc.nasa.gov/Videos/general/blackhole.mov




Timeline of discoveries involving the Black Hole
Person
Year
Discovery
John Michell
1783
First suggested the concept of a black hole
Simon Pierre LaPlace
1796
Suggested the possibility of stars that could be black holes and predicted that there could be bodies in the universe that are invisible
Albert Einstein
1915
published the theory of general relativity; he predicted space time curvature
Karl Schwarzchild
1916
Described the singularity structure and discovered the point mass and used Einstein’s theory
Subrahmanyan Chandrasekhar
1928
Hypothesized that a dying star could trap light
Robert Opppenheimer
1939
Developed possible explanation for the points with infinite density
John Wheeler
1964
Coined the term ‘black hole’
Stephen Hawking
1970
Defined the modern theory of black holes
Cygnus X – 1
1970
The first probable black hole was discovered and named Cygnus X – 1. It emits x rays and its composition is smaller than Earth.
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more on the discoverers:
John Michell

- discussed the possibility of a star with a gravitational force so strong that not even light could escape it
- this prevented astronomers from observing it

Marquis de Laplace
- French scientist
- the possibility of such stars his book The System of the World

Karl Schwarzchild
- German physicist
- wrote a paper describing a structure called a singularity
- contended that a matter could theoretically be drawn into a point with virtually no volume and an infinite density.
- called this object a point mass, later known as a singularity
- determined that there is a definite boundary around a singularity called the event horizon
- used Einstein’s theory to define what a black hole is.

Subrahmanyan Chandrasekhar
- hypothesized that a dying star of a certain mass might form a point with enough gravitational pull to trap light
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Properties of Black Holes
Black holes have surface area and a pull of gravity.
-the surface area of the event horizon of a black hole can only increase, never decrease. So, although two black holes can join to make a bigger black hole, one black hole can never split in two.

-The pull of gravity at the event horizon is constant; it has the same value everywhere on the event horizon

Black holes have an event horizon, a radius, and singularity.


The
Event Horizon is the area surrounding a black hole where the escape velocity is equal to the speed of light. The escape velocity is the velocity that would be needed to escape the gravitational field of the black hole. The event horizon is represented as:
Event Horizon = c = (3.0E^10)
The event horizon can be thought of as a massive sphere, or the "surface" of the black hole, even though the black hole's mass all lies within this surface.

The Schwarzschild Radiusis the distance from the center of a black hole to its event horizon. Russian physicist Karl Schwarzschild calculated this distance, and the radius can now be calculated with this equation:
In the equation

M= the mass of the black hole
G=the universal gravitational constant

C=the speed of light
The "radius" is the distance from the center of the black hole, singularity, to the edge of the black hole, the event horizon.

The Singularity is located at the direct center of a black hole. It is a place of infinite space time curvature. This point exists because the star's entire density is being crushed to a single point, thus having infinite density.
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The picture below depicts the event horizon, the Schwarzschild child radius, and singularity of a black hole
.

external image singular.jpg

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Black Holes are characterized by three properties:
1. Mass
2. Spin
3. Electrical Charge


Mass classes:
Stellar black hole- star-sized and range in the 10-100 solar mass range
Super massive black hole- they are located at the cores of what appear to be every large galaxy, including our Milky Way. They range in the millions to billions of solar masses.

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Other Types of Black Holes

external image Schwarzschild_black_hole.gifSchwarzschild Black Holes

Schwarzschild black holes are the simplest type of black hole. They have two main components, a singularity and an event horizon. The singularity is what is left of the collapsed star, and is theoretically a point of 0 dimension with infinite density but finite mass. The event horizon is a region of space that is the "boundary" of the black hole. Within it, the escape velocity is faster than light, so it is past this point that nothing can escape. 7









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Reissner-Nordstrøm Black Holes

A more complex hole is the Reissner-Nordstrøm black hole. It has the singularity and two event horizons.
Embedding diagram of the Reissner-Nordström geometry with Charge/Mass = 0.9.
Embedding diagram of the Reissner-Nordström geometry with Charge/Mass = 0.9.

The outer event horizon is a boundary where time and space flip. This means that the singularity is no longer a point in space, but one in time. The inner event horizon flips space-time back to normal. 9















external image stars_blackhole_anatomy.jpgKerr Black Holes
A Kerr black hole has another feature called an ergosphere. The ergosphere is in an ellipsoidal region outside the event horizon. The ergosphere is the last stable orbit, and the outer boundary is called the static limit. The faster the black hole rotates, the larger the inner event horizon becomes. The outer event horizon remains the same size. They become the same size when the rotational energy equals the mass energy of the black hole. If the rotational energy became more than the mass energy, the event horizons would dissappear and a "naked singularity" would be left, which is a black hole that only has a singularity.
Another feature of the Kerr black hole is that the 0-D point that is the singularity in the Schwarzschild and Reissner-Nordstrøm black hole is spun into a ring of 0 thickness. However, nothing can actually fall into it unless it enters along a trajectory on the ring's side. At any other angle the ring produces an antigravity field that repels matter. 10








What Makes Up A Black Hole

Albert Einstein's theories states that black holes are made of pure gravitational energy. They have mass and spin, but contain no matter. Anything that falls into a black hole is converted to energy. So, a black hole is made up mostly of energy.
Black holes are a point of infinite density. They do not have a surface, and are not dark, black orbs like they are sometimes portrayed to be.

check out this video of the journey into a Schwarzschild black hole!

Journey into a Schwarzschild black hole from Andrew Hamilton on Vimeo.



Influence of Gravity

Black holes are areas of concentrated mass, mass so enormous, that the force of gravity will not let anything within a certain area around it to pass. The strong pull of gravity does not even allow light to pass through.
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video: http://www.space.com/common/media/video/player.php?videoRef=black_holes

Black Hole Stories

January 8, 2007
070108_tripleblackhole_01.jpg

Three distant super-massive black holes were spotted. These extremely bright objects, known as quasars, are presumed to be powered by the falling of gas into enormous black holes that are positioned in the centers of galaxies. One single quasar can outshine an entire galaxy, even though it is smaller than our solar system.
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December 6, 2006

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For the first time scientists have captured the entire process of a black hole consuming a stellar meal. A telescope that was orbiting, known as the Galaxy Evolution Explorer, detected bright ultraviolet flares, assumed to be emitted from star that had unfortunately traveled too close to the black hole and began to fall into it. This event rarely happens and the scientists were lucky to get the chance to study the entire process, from the beginning to the end.
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January 3, 2007

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Astronomers spotted a black hole in the middle of a tightly packed star cluster, which is not the typical location for a black hole. This black hole is about 10 times more massive than our sun! It is located around 50 million light-years from the Earth, in the Virgo Cluster.
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April 6, 2006

hf_blackholes_merge0406_04.jpg
Astronomers have discovered two black holes that have been seen to be spiraling toward a merger. If a collision were two occur, it will create a super-massive black hole which will have the presumed capability to swallow material equivalent to billions of stars. Mergers between black holes are thought of as one way that black holes form.
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Speculations


To be “sucked” into a black hole, an object would have to cross inside the Schwarzschild radius. At this radius, the escape speed is equal to the speed of light, so when light passes through, it would be unable to escape.
The Schwarzschild radius can be calculated using the equations for escape speed:
vesc = (2GM/R)1/2

How do we even know that they exist?

Stellar black holes are relatively small. They are presumed to be only a few to a few tens of kilometers in size. We are unable to see black holes because the light that would enable us to see them cannot escape.
If a black hole were to pass through a cloud of interstellar matter, or if it comes close to another star, the black hole can “consume” matter into itself. Matter is caused to fall into the hole, as if it pulled towards that black hole. As the matter falls, it experiences an increase in kinetic energy, and as a result it is called to heat up. The heating causes for an ionization of atoms, and when the atoms reach a large enough heat, they emit X-rays. These X-rays are sent off into space before the matter crosses the Schwarzchild radius, thus we can see this X-ray emission, not the actual black hole. 16


Where can we find Black Holes?

It is impossible to observe a black directly, so black holes have to be identified by their effect on the matter that surrounds them.

Theories

General Theory of Relativity: the principle that the speed of light in a vacuum is constant.

Video Intro to Black Holes and a Really Cool Website!!

Explore this website to learn more about black holes! J
Black Holes: Gravity’s Relentless Pull:
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White Holes

worm.gif wormhole01.jpg
Schwarzschild Wormhole

What is a White Hole?

A white hole is a time reversal of a black hole. White holes appear as part of the vacuum solution to the Einstein field equations that describes a Schwarzschild wormhole which draws in matter, and the other side is a white hole which emits matter. These Schwarzschild wormholes do not connect white holes and black holes. The wormholes disconnect as soon as they form, therefore showing that they are unstable. It is very doubtful that there can be an existence of white holes without being a part of a wormhole. If a white hole existed that was not a part of a wormhole, it would violate the second law of thermodynamics.

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What is the Difference Between a White Hole and a Black Hole?
A white hole can be referred to as an “anti-black hole.” Black holes are where matter is sucked in, and white holes are where matter is ejected out. The concept of white holes is theoretical and it is not widely renowned.

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The universe is emerging from a white hole, because unlike the black holes, white holes throw the matter out. People wonder if there is a connection between the mass that disappears into a black hole and the mass that emerges from a white hole.
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What Does a White Hole Do?

The black hole sucks up the matter that crosses the event horizon, and a white hole emits the matter from its event horizon. Both black and white holes attract matter. Black hole event horizons only “suck up” matter. To observers, white holes and black holes are impossible to be told apart.
Black holes emit Hawking radiation in quantum physics. Because of this, the black holes can come to thermal equilibrium with a gas of radiation. A thermal equilibrium state is a time reversal constant. Hawking said that a time reversal of a black hole in thermal equilibrium is again a black hole in thermal equilibrium. If this was true, then black holes and white holes would be known as the same thing.

A cosmological type of white hole can be known as the initial feeding of matter from the parent universe’s black hole and the expansion of the new universe. This is different than most white holes because it would not be located in space. Also, this white hole would be recognized with the cosmological horizon. In cosmology, a cosmological horizon marks a limit to observability, and marks the boundary of a region that an observer cannot see into directly due to cosmological effects. 21


References



1-http://burro.astr.cwru.edu/stu/stars_blackhole.html
2- http://amazing-space.stsci.edu/resources/explorations/blackholes/lesson/whatisit/history.html
3- http://library.thinkquest.org/C0110369/History.htm
4- http://hepguru.com/blackholes/characteristics.htm
5-http://hepguru.com/blackholes/characteristics.htm

6-http:amazing-space.stsci.edu/resources/explorations/blackholes/lesson/whatisit/types.html
7- http://burro.astr.cwru.edu/stu/advanced/stars_blackhole.html
8- http://zebu.uoregon.edu/~imamura/FPS/images/Schwarzschild_black_hole.gif
9- http://casa.colorado.edu/~ajsh/rn.html
10-http://burro.astr.cwru.edu/stu/advanced/stars_blackhole.html
11 - http://www.space.com/blackholes/
12 - http://www.space.com/scienceastronomy/070108_blackhold_triple.html
13 - http://www.space.com/scienceastronomy/061206_blackhole_meal.html
14 - http://www.space.com/scienceastronomy/070103_gcluster_bh.html
15 - http://www.space.com/scienceastronomy/060406_blackhole_merge.html
16 - http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
17- http://hubblesite.org/explore_astronomy/black_holes/

18 -
http://www.bookrags.com/wiki/White_hole
19 - http://scitech.blogs.cnn.com/2009/04/27/the-strange-concept-of-white-holes/
20 - http://richlabonte.net/exonews/xtra2/dark_energy.htm
21 - http://www.statemaster.com/encyclopedia/White-hole