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 * Black Holes and Tides **
 * (http://www.cosmographica.com/gallery/portfolio2007/content/131_BlackHole_large.html) **
 * __Black Holes __**

**__Definition: __** In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, including light, can escape its pull ([]). More simply, a black hole is an ordinary space where gravity has gotten to the extreme where it engulfs all other forces, including light. Nothing can escape a black hole’s force.

 The arrows show the path of objects in and around the black hole. ( [] ).


 * __Anatomy of a Black Hole __**

The anatomy of a black hole is relatively simple. First off there are two types of black holes. There is the Schwarzschild black hole, which is a non-rotating black hole, and there is the Kerr black hole, which is a rotating black hole and the most common type of black hole found in nature. The Kerr black hole is a rotating black hole. It rotates because the star that is formed from was a rotating star and when this star collapses its core continues to rotate. The Kerr black hole has several parts to it. The **singularity** is the collapsed core and it is the center of the black hole where the mass of the star lies. Here the force of gravity is infinitely strong. As we move out of the black hole we come next to the event horizon. The **event** **horizon** is commonly known as the opening of the black hole. At the event horizon everything, including light, it brought into the black hole. Neither the singularity nor the event horizon are tangible objects and everything that passes the event horizon into the black hole will eventually reach the singularity. The **ergosphere** can only be found in a Kerr (or rotating) black hole and it is the place where all particles are pulled into the rotational path of the black hole. At this point matter and energy are still able to escape the black hole. The outer edge of the ergosphere is called the **static** **limit**, which is the distance matter must maintain to prevent from being pulled into the black hole’s rotation.

(http://burro.astr.cwru.edu/stu/stars_blackhole.html).


 * __ Formation of a Black Hole __**

A black hole is most often formed at the end of a star’s life cycle. When a star of sufficient mass doesn’t produce enough energy to balance the attractive, collapsing force of its own gravity a black hole is formed (Mr. Melograna’s notes). Its gravity causes it to collapse into an infinitely small space. ** Stellar black holes ** are formed when a massive star collapses.
 * Supermassive black holes ** are guessed to exist in the center of almost all galaxies, including the Milky Way, but scientists are uncertain as to how these black holes are formed. It can be guessed that they are a byproduct of galaxy formation.
 * Miniature black holes ** have never been found but some assume they formed shortly after the “Big Bang”. A miniature black hole would have a mass much smaller than the sun.


 * __Black Hole History __**

In 1738 John Michell inferred that there might be an object massive enough to have an escape velocity larger than that of the speed of light. In 1796 Simon Pierre LaPlace predicted the existence of black holes. In 1915 Albert Einstein published his Theory of General Relativity and a year later Karl Schwarzchild used this theory to define a black hole. In 1964 John Wheeler coined the term “black hole”. In 1970 Stephen Hawking defined the modern theory of black holes. In 1970 Cygnus X – 1 became the first good black hole candidate. In 1994 the Hubble Space Telescope began providing evidence of supermassive black holes.


 * __Properties of Black Holes __**

Black holes can be measure by three properties: <span style="font-size: 12pt; color: #e36c0a; mso-bidi-font-family: Calibri; msobidifontfamily: Calibri; mso-themecolor: accent6; msothemecolor: accent6; mso-themeshade: 191; msothemeshade: 191; mso-bidi-theme-font: minor-latin; msobidithemefont: minor-latin; msolist: Ignore;"> 1. <span style="font-size: 12pt; color: #e36c0a; font-family: Calibri; mso-themecolor: accent6; msothemecolor: accent6; mso-themeshade: 191; msothemeshade: 191;">Mass <span style="font-size: 12pt; color: #e36c0a; mso-bidi-font-family: Calibri; msobidifontfamily: Calibri; mso-themecolor: accent6; msothemecolor: accent6; mso-themeshade: 191; msothemeshade: 191; mso-bidi-theme-font: minor-latin; msobidithemefont: minor-latin; msolist: Ignore;"> 2. <span style="font-size: 12pt; color: #e36c0a; font-family: Calibri; mso-themecolor: accent6; msothemecolor: accent6; mso-themeshade: 191; msothemeshade: 191;">Electric Charge <span style="font-size: 12pt; color: #e36c0a; mso-bidi-font-family: Calibri; msobidifontfamily: Calibri; mso-themecolor: accent6; msothemecolor: accent6; mso-themeshade: 191; msothemeshade: 191; mso-bidi-theme-font: minor-latin; msobidithemefont: minor-latin; msolist: Ignore;"> 3. <span style="font-size: 12pt; color: #e36c0a; font-family: Calibri; mso-themecolor: accent6; msothemecolor: accent6; mso-themeshade: 191; msothemeshade: 191;">Rate of Rotation For example Schwarzchild black holes are non-rotating and therefore have zero spin/rotation and they have zero charge.


 * __ What happens if you get too close to a black hole or fall into a black hole? __**

In a stellar black hole a strong “tidal” pull is exerted on any object that approaches the black hole’s horizon. That is the same effect that creates the tides on Earth: the gravitational pull on the side of the object that is closest to the black hole is significantly stronger than the pull on the opposite side, so gravity stretches the object and pulls it apart ([]).

A  **wormhole** is a hypothetical spacetime topology, a "shortcut" that would allow travel between two points at apparently faster-than-light [|speeds]. ([]). In actuality wormholes probably do not exist, but this idea is popular in science fiction novels, but if wormholes did exist they would be able to function as time machines. A **white** **hole** is the theoretical [|time reversal] of a [|black hole]. While a black hole acts as a vacuum, drawing in any [|matter] that crosses the [|event horizon], a white hole acts as a source that ejects matter from its event horizon ([]).
 * __ Wormholes and white holes __**

<span style="font-size: 12pt; font-family: Calibri; mso-bidi-font-family: Arial; msobidifontfamily: Arial;"> ( [] ).

<span style="font-size: 12pt; color: #1f497d; font-family: Calibri; mso-themecolor: text2; msothemecolor: text2;">Our sun cannot become a black hole because it does not have the minimum mass necessary to reach the point of becoming a black hole. The closest black holes yet discovered are several thousand light-years away. They are so far that they have no effect on Earth or its environment. A supermassive black hole appears to inhabit the center of the Milky Way galaxy, about 27,000 light-years away. Although it is several million times the mass of the Sun, its great distance insures that it won't affect our solar system ( [] ). <span style="font-size: 12pt; color: #1f497d; font-family: Calibri; mso-themecolor: text2; msothemecolor: text2; mso-ansi-language: EN; msoansilanguage: EN;">If two black holes were to collide they will likely merge and become a larger black hole. This would be a very violent event and we cannot fully understand it. In 1974, Stephan Hawking found out that there was thermal radiation in black holes, showing that they aren't completely black. He did so by using a quantum field theory and the effect he found became known as Hawking Radiation (http://en.wikipedia.org/wiki/Black_hole#Black_hole_unitarity).
 * __<span style="font-size: 14pt; color: #1f497d; font-family: Calibri; mso-themecolor: text2; msothemecolor: text2;">Fun Facts __**

For some hands on experience visit <span style="font-size: 12pt; font-family: 'Calibri','sans-serif'; mso-fareast-font-family: Calibri; mso-bidi-font-family: 'Times New Roman'; mso-bidi-theme-font: minor-bidi; mso-ansi-language: EN-US; mso-ascii-theme-font: minor-latin; mso-fareast-theme-font: minor-latin; mso-hansi-theme-font: minor-latin; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">[]