~Black Holes~Web Page Created by Rohan Bhatt


Introduction:


On earth, we feel the regular pull of gravity that keeps things on the ground.
If, say on a space mission, we want to overcome that gravity, a rocket ship can go fast enough to exceed gravity's pull.
BUT...say earth was shrunken down to the size of a marble. Now, earth's gravity would be so strong that not even light can escape it:
BH1.jpgBH2.jpg BH3.jpg
This is called... A BLACK HOLE



What Exactly is a Black Hole?

Black-Hole-s-Galaxy-M64-space-3031378-520-584.jpgA black hole is an object that is so COMPACT (enough mass in a small enough volume), that its gravitational force is strong enough to prevent anything from escaping. The existence of black holes was first proposed in the 18th century, based on the known laws of gravity. The more massive an object, or the smaller its size, the larger the gravitational force is.
(A very massive object) + (A tiny space) = STRONG gravitational force.
A black hole forms when massive but otherwise normal stars die out. We cannot directly see black holes but we can detect material being sucked into them.




Do Black Holes Obey the Laws of Physics?

Image1_med.gifBlack holes do obey all the laws of physics...INCLUDING the laws of gravity.
Although gravity is one of the weaker forces in our universe, it shapes what we know as our world and solar system.

Einstein's theory of general relativity:
  • Space and time must be connected.
  • Massive objects distort the four-dimensional space-time continuum. This distortion is gravity.

Einstein's theory can explain a lot of the physics of black holes.




How Big is a Black Hole?

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All matter in a black hole is squeezed into a region of INFINITELY small volume.
  • This center is called the central singularity.There is an imaginary ring around a black hole that marks how close you can safely get before it is impossible to escape its pull.
  • This sphere is called the event horizon. The size of this sphere is proportional to the mass of the black hole.

Event horizon's have been found ranging from 6 miles to the size of our solar system.





Are There Types of Black Holes?

Black holes differ mostly because of their surroundings. They differ based on:
  • mass of the black hole
  • spin of the black hole (whether and how fast it rotates around an axis)
  • electric charge of the black hole
There are two main types: Stellar-Mass, and Supermassive black holes.
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Stellar-Mass black hole (just a few times heavier than our Sun)
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Super Massive black holes (as heavy as a small galaxy)



What Does a Black Hole Look Like When Orbiting?

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Simulated view of a close up black hole
Light rays that pass close to a black hole are caught and sucked in. Therefore, the region around a black hole is a small dark disk. It is impossible, however to get close enough to photograph this dark circle.

Light rays that pass a little further away are caught and BENT by the black hole's gravity. This distorts the star field around the black hole.

Because of this, you would be able to see two duplicate images of the same star on opposite sides of the black hole, because of the bending of light.





What is Inside of a Black Hole?

Unfortunately, we cannot say. This would involve a mixture of gravitational theory, with the theory of quantum mechanics. Because these two theories are on such different scales, we cannot make these kinds of predictions. Einstein thought maybe all matter is piled up in a single point at the center, and that maybe then this is a wormhole to another universe. However, these eccentric ideas cannot be tested.
What if you jumped into a black hole?
mod3_q16_2.jpg1. You start falling outside the horizon of the black hole. You see a center of perfect darkness. The pattern of stars around the circle is strangely distorted, as light is bent.

2. You accelerate faster and FASTER towards the center, pulled by gravity.

3. Your body is stretched apart and elongated by gravity. As you get closer, your body is completely torn apart before you reach the event horizon.

4. As soon as you fall through the event horizon, you are SQUASHED into a single point of infinite density.


How are Black Holes Born?

An exploded star (Supernova)
An exploded star (Supernova)
A black hole is born when an object becomes unable to withstand the compressing force of its own gravity.

Stellar-mass black holes are born with a bang. They form when a very massive star runs out of nuclear fuel. The star then explodes as a supernova.
Most of the stellar material is blown away by the explosion. The resulting black hole is only a few times heavier than our Sun.

Supermassive black holes' births are unknown.





Important Discoverers/People?
John Archibald Wheeler first termed "black hole" in 1967.
Isaac Newton showed that all objects in the Universe attract each other through gravity in 1687.
Albert Einstein refined the idea of gravity through his theory of general relativity.
Karl Schwarzschild first discovered the solutions of equations of general relativity that describe black holes MATHEMATICALLY. The radius of the event horizon is termed the Schwarzschild Radius, after him.




Sources:
1. "HubbleSite: Black Holes: Gravity's Relentless Pull." HubbleSite - Out of the ordinary...out of this world.. N.p., n.d. Web. 9 Apr. 2011. <http://hubblesite.org/explore_astronomy/black_holes/home.html>.