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Black Holes

Page history last edited by Katelyn 13 years, 1 month ago

 Black Holes




Table of Contents

1. What is a Black Hole?

2. Creation of Black Holes

3. The Physics Behind it All

4. Components of Black Holes

5. Types of Black Holes

6. What Happens if You Fall into a Black Hole?

7. Evidence to the Existence of Black Holes

8. Bibliography


What is a Black Hole?

Although there are many mysteries of the universe that remains unanswered, black holes were and to this day are one of the more mind-boggling of phenomenons. As children we discovered that black holes are large dark masses scattered within space acting as a vacuum, devouring everything in its path. In essence these beliefs are not that different from the truth…only a bit more complicated. Where vacuums are areas without matter that suck in matter from surrounding higher pressure areas, Black holes are concentrated amounts of matter in a relatively small space. Instead of a vacuum force pulling in everything in sight, black holes are black because their gravitational pull is strong enough to prevent everything - even light rays- from escaping.

Creation of Black Holes

A black hole’s existence begins when a star’s existence ends. Theories state that a black hole can be created when a very massive star is about to go supernova. At this point the nuclear fuel of the star is exhausted and there is not enough energy present to feed the star. The star then cannot support itself against the massive amounts of pressure present inside it, thus the star begins to reduce in size. The star continues to shrink until it reaches a crucial magnitude known as Schwarzschild radius. (The Schwarzschild radius is the distance that defines the size of which a star becomes a black hole.) At this stage the star implodes by collapsing into itself, resulting in a black hole.

note: planets are also subject to this process. When the nuclear reactions within them can't sustain their round shape against gravity and they are sized such that the velocity needed to escape their g-field matches or exceeds the speed of light. 



(here is a question in which you can determine whether or not a mass is a black hole)


Why so Strong?

Black holes are surrounded by several strains of physics like: special relativity, the equivalence principle of general relativity, world line, Kepler's law, gravitational lensinggravitational waves, frame-dragging, geodetic effect and more. These are all exciting areas of physics, but the area of study that connects us with field forces is gravitational pull.


A Black Hole is formed when the gravitational pull of an area is so strong that not even light can escape. To a basic level, this force (gravitational pull) is calculated by the equation




In this equation Fg and m are directly proportional, meaning the greater the mass the stronger the force. Also, Fand d are inversely proportional, meaning the smaller the volume (smaller "d" (distance) ) the greater the gravitational force. Black Holes are very compact objects, meaning they posses both a great mass and a small volume. The combination of these two characteristics make the force of Black Holes very very strong. Hypothetically speaking, if the Earth is squeezed to the size of a marble, it'll become a Black Hole.   


Components of Black Holes


It is believed that in the center of the black hole lies a singularity with a gravitational field around it. A singularity is a tiny point of infinite density and volume, where time and space become distorted according to the theory of general relativity published by Albert Einstein in 1916.



The event horizon borders the black hole; its escape velocity is equal to the speed of light. Anything that crosses the event horizon cannot escape because it is believed that nothing can surpass the speed of light. Beyond this point, nothing outside the event horizon can observe the object.



On earth, we feel the greatest amount of gravitational force (Fg) when we are on its surface because we are closest to the earth’s total mass. By getting closer to the core of our plant and digging underground the Fg decreases because it exposes less of its mass to us. The effect of gravitational force on black holes is the same to the gravitational force on the earth and stars. From a large distance away from a black hole you would feel the effects of the gravitational pull as you do on earth. However a black hole is infinitesimally small, so the gravitational pull is very strong because an object can get extremely close to it and still be exposed to its total mass. Once you pass the event horizon the object cannot escape unless it can travel faster than the speed of light, but still to this day nothing can travel faster than the speed of light.


Escape velocity equation:Schwarzschild Radius question.txt

Ve=√ (2GM/R)  c


Ve: the escape speed

G: the Universal Gravitational Constant (6.674 x 10-11 m3 kg-1 s-2)

M: the mass of the black hole (kg)

R: the separation of the center of the black hole and the center of the object with respect to the black hole (Km)

c: speed of light in a vacuum (2.99 x108m/s)


It is hypothesized that an object must travel faster than the speed of light in order to escape the black holes Fg. Therefore if √ (2GM/R) is greater than the speed of light then nothing can escape the black hole.



Ergospheres appear in rotating black holes and are surrounded by a region of spacetime in which it is impossible to stand still. This is the result of a process known as frame-dragging; any object near the rotating mass will tend to start moving in the direction of rotation. The ergosphere lies outside the event horizon but inside the stationary limit of a Kerr black hole.



A region bordering the outside of a black hole in which particles cannot remain at rest and must travel with the black hole.



Types of Black Hole

Schwarzschild Black Hole:

      This is the simplest type of black hole. It is spherical, static and non-rotating.


Kerr Black Hole: 

 This is the most common form of black hole that is found naturally. It is a spherical, rotating because the star that previously existed also rotated; when the star collapsed the core continued to rotate. Unlike the Schwarzschild black hole with a point singularity, a Kerr black hole has a ring singularity surrounded by a gravitational field.  Because the black hole is spinning, the singularity is not fixed in the center because of centrifugal forces. The centrifugal force distorts the singularity into a ring-like region found in the plane of rotation in the black hole.                                                                                            

 Image of a Kerr Black Hole


What Happens if You Fall into a Black Hole? 

Once you get caught in the event horizon, you will be forced to travel closer and closer to the core. The gravitational pull would be so great creating a tidal force. The gravity acting on your head would be much stronger than the gravity acting on your toes (assuming you were falling head-first). That would make your head accelerate faster than your toes; the difference would stretch your body until it snapped apart, first at its weakest point and then disintegrating rapidly from there as the tidal force became stronger than the chemical bonds holding your body. Scientists agree, and so do we, that falling into a black hole is inadvisable.  









Huge gravitational fields like black holes also have an interesting effect on time. Check it out here: http://hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q15.html     

Evidence to the Existence of Black Holes  

The black hole was first theorized in 1790 by John Michell of England and Pierre LaPlace of France. By using Newton’s Laws they suggested the existence of an “invisible star”.


(John Michell & Pierre LaPlace) 


As mentioned earlier, no light can be observed from a black hole, hence the name “black hole”. So how does the world know that black holes are not an invented phenomenon?


The discovery of black holes is based on the velocity measurements of a whirlpool of hot gas and in some cases other stars that orbit the black hole. The speed of the gas indicates the speed of the rotation of the black hole.  


The matter that surrounds the black hole emits radiation that can be detected using a Space Telescope imaging Spectrograph (STIS). A spectrograph uses prisms to divide the incoming light into fragments of light; this tells scientists how fast the gas is swirling at that location. The faster the rotation the greater the mass of the  core is. If the mass is great enough, it is estimated that a black hole is present





The Question: in PDF

Other Helpful Links








 Ron Kurtus (revised 8 February2011). "Gravitational Escape Velocity for a Black Hole by Ron Kurtus - Succeed in Understanding Physics: School for Champions." School for Champions: online lessons for those seeking success. N.p., n.d. Web. 20 Apr. 2011. http://www.school-for-champions.com/science/gravitation_escape_velocity_black_hole.htm.


"Answers.com - What happens when you go into a black hole." WikiAnswers - The Q&A wiki. N.p., n.d. Web. 20 Apr. 2011. <http://wiki.answers.com/Q/What_happens_when_you_go_into_a_black_hole>.

Freudenrich, Craig, and  Ph.D.. "HowStuffWorks "How Black Holes Work"." Howstuffworks "Science". N.p., n.d. Web. 20 Apr. 2011. http://science.howstuffworks.com/dictionary/astronomy-terms/black-hole2.htm.


"General relativity - Wikipedia, the free encyclopedia." Wikipedia, the free encyclopedia. N.p., n.d. Web. 20 Apr. 2011. http://en.wikipedia.org/wiki/General_relativity.


"Schwarzchild Radius." Sky Books - "Where Science Fiction Meets Reality". N.p., n.d. Web. 20 Apr. 2011. <http://www.skybooksusa.com/time-travel/timeinfo/schwarzc.htm>.

Thompson, Andrea. " What Is A Supernova? | Space.com ."  Space, NASA Information & News | Outer Space Flight Videos & Pictures | Astronomy, Solar System Images | Space.com . N.p., n.d. Web. 20 Apr. 2011. http://www.space.com/6638-supernova.html.


"What is a ring singularity? ." The Astronomy Cafe : Dr. Sten Odenwald - A resource for learning about astronomy. N.p., n.d. Web. 20 Apr. 2011. http://www.astronomycafe.net/qadir/ask/a11260.html.


"black hole - definition of black hole by the Free Online Dictionary, Thesaurus and Encyclopedia.." Dictionary, Encyclopedia and Thesaurus - The Free Dictionary. N.p., n.d. Web. 20 Apr. 2011. <http://www.thefreedictionary.com/black+hole>.

nothing, seeing almost, and astronomers say they've. "New Evidence for Black Holes  - NASA Science." NASA Science. N.p., n.d. Web. 20 Apr. 2011. <http://science.nasa.gov/science-news/science-at-nasa/2001/ast12jan_1/>.



Images Sources







Comments (8)

Nancy Xiao said

at 12:20 am on Apr 19, 2011

Nima said

at 3:47 pm on Apr 20, 2011

okay guyz, i cant put any other pictures onto the wiki...i dont know why ;S

Nima said

at 4:01 pm on Apr 20, 2011

kaitlin, can you make the wiki look nice and professional
Nancy can you finish the question: remember that the question needs realistic numbers (eg, the mass of the satellite should be almost exact)

Katelyn said

at 6:44 pm on Apr 20, 2011

sounds good. Nancy, if you're having issues with the question, let me know and I can do one. I've got a pretty solid idea.

Nima said

at 6:52 pm on Apr 20, 2011

katrlyn if u have have any other links PLEASE add them lol

Nima said

at 7:27 pm on Apr 20, 2011

what do u think of the wiki so far?

Nima said

at 9:07 pm on Apr 20, 2011

remember nancy,Mr B wants a question that involves math with realistic numbers...and he wants it attached to the wiki on a word or pdf file

Nima said

at 6:42 am on Apr 21, 2011

Great job katelyn and nancy!!!!!!!!!!!!!!!!! we sure pulled off this assignment nicely ;P

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