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Black Holes

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Jessifer Duncan-Raye

on 4 February 2014

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Transcript of Black Holes

How are Black Holes Formed?
Parts of a Black Hole
What is a Black Hole?
­A region of space where gravity is so 
strong that nothing can escape from it, 
not even light
­Immense amounts of matter have 
been compressed into a minuscule 
amount of space, which is why the 
gravitational pull of black holes is so 
Black Holes
Kerr Black Holes
Also known as rotating black holes
A non-rotating black hole = Schwarzschild black hole
By Stephanie Gu & Jessica Long
Stellar Black Holes
They form from the supernova of a very massive star (x 20 our Sun)
Stars convert H into He through nuclear fusion, the energy generated keeps core from collapsing
Star keeps on fusing heavier elements
Reaches iron, which cannot be fused b/c it takes more energy to fuse than is produced
The core of the star collapses under its own weight
Becomes very dense -> huge gravitational pull
Supermassive Black Holes
It is theorized that all galaxies contain a supermassive black hole at their centers
Can have masses of millions or billions of stars
Mystery as to exactly how they were formed
May begin as normal black hole, accumulating matter over time
Or may result from collision of two galaxies, the black holes in their centers eventually merging
Mini Black Holes
Less than x3 mass of our Sun
Can be as small as an atomic particle
Needs outside pressure to assist in creation - may not be massive enough to collapse on its own
The smallest black holes may have formed during the creation of our universe
The "hole" itself
Very center/core of black hole
Where the mass lies
Where space-time has infinite curvature
Where gravitational pull is infinitely strong
Event Horizon
Opening of the black hole
Escape velocity = speed of light
Cannot escape once one passes the event horizon
To a person entering the black hole, time flows normally
To an observer, the person would slow down and get redder and dimmer, then disappear
Region of space around the black hole
Spacetime is "dragged" in the direction of rotation faster than light
General relativity theory: rotating mass drags surrounding space-time with it
An object cannot maintain a fixed position unless it is faster than light
Size is determined by gravitational pull & rotation of the black hole
The boundary between ergosphere and normal space is called the static limit
Located outside of event horizon, so matter can escape
Formed from a rotating star
Most common form of black holes in nature
Ring shaped singularity
Accretion Disk
Accretion Disk is created by matter orbiting the black hole, which will be gradually be pulled in
­Particles of gas and dust collide with each other as they spiral around the black hole
The matter is heated up by these 
collisions, and they may get hot enough 
to emit X­-rays
Gas Jets
Jets of hot gas have been found gushing out of 
the area surrounding a black hole
They flow perpendicular to the accretion disk and 
can be millions of light years long
They form just outside the event horizon where  temperatures and magnetic fields are the most  potent
Are the result of charged particles spinning around 
the powerful magnetic field lines believed to
revolve around black holes
Seen around many but not all black holes

Other Types

Reissner–Nordström: Charged, non rotating,
Kerr-Newman Black Hole: Charged, rotating
Unlikely to exist since stars (which create black holes) are usually not charged
Outer event horizon: boundary of black hole, escape velocity = light speed
Inner event horizon (Cauchy horizon): time and space revert mostly back to normal, possible to avoid singularity
The more charge the black hole acquires, the smaller the outer event horizon and the larger the inner event horizon gets.
If charge is high enough, horizons merge
Can go through a wormhole and come out a white hole

Charged Black Holes

Look for effects of gravity of the black hole e.g. stars rotating around something invisible
Gravitational lens: an object with immense gravity bends light, causes arcs and rings of light to appear
X-rays: generated by the very hot matter found in accretion disks circling black holes

How We Detect Black Holes
White Holes and Wormholes
White hole: opposite of black hole - ejects matter
Wormhole: connects black hole to white hole
Possible to use worm hole for time travel, travel to alternate universe
Never observed, unlikely to exist, extremely unstable
Reissner-Nordstrøm Black Hole
(Excluding Photon Sphere)

Important Scientists
1915: Published his Theory of General Relativity
Gravity is not a force, but the curvature of space and time.

Albert Einstein
Karl Schwarzschild
Used Theory of General Relativity to develop the concept of black holes.
Determined the minimum radius that an object with a specific mass must have in order to achieve an escape velocity that would be greater than the speed of light
This radius is called the "Schwarzschild Radius"
Sir Isaac Newton: Described gravity in "Philosophiae Naturalis Principia Mathematica"in 1687
1783, John Michell: Proposed the idea of a star whose gravity is so great that not even light could escape
1795, Pierre Simon Laplace: Calculated that if an object were to be compressed into a small enough radius, the escape velocity of that object would need to be faster than the speed of light.
1935: Determined the greatest mass that a star can have without collapsing and exploding in a supernova
This mass is called the "Chandrasekhar Limit"
Important in star evolution
If the mass of a star surpasses this limit, the star wouldn't become a white dwarf, and this led to the discovery of neutron stars and black holes
Subrahmanyan Chandrasekhar
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Bibliography Continued

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Full transcript