The Seekers
Introduction
Terminology “black hole” was introduced by John Wheeler in 1967.
Black hole – A region in the space where the gravitational pull is so strong that neither substance nor light can leave this area.
Around a black hole there is a surface called an event horizon that marks the point of no return.
History of Ideas
In the 18th century John Michelle and Pierre-Simon Laplace mentioned about the objects with a huge gravitation, from which even light cannot escape.
In 1915 Albert Einstein developed the theory of general relativity.
Karl Schwarzschild finds black holes as a solution to Einstein’s equations (1916).
Robert Oppenheimer and Hartland Snyder predict that massive stars can collapse into black holes (1939).
What Are Black Holes?
A black hole is a great amount of matter packed in a very small area
such a big gravitational field, that nothing, not even light can escape
can’t directly be observed - only way to perceive them is by detecting their effect on other matter nearby
attracted matter accelerates & heats up - emits x-rays that radiate into space, emitting powerful gamma rays bursts - devour nearby stars.
Formation
many theories about formation
The most obvious way of black hole - the core collapse of massive stars (Mass >= 3 x mass of sun).
a gigantic star reaches final stage of its life - about to go supernova - spends all the nuclear fuel by then
stops burning and heating up - cannot create the nuclear energy required to feed the star
gets crushed under its own gravity, leaving behind a black hole.
Gravity deforms Space
Time
Gravity Bends The Path Of
Light
Types of Black
Holes
Miniature black holes:
event horizons as small as atomic particles
Created during the Big Bang
compressed into a really small point -later exploded creating a massive explosion.
Super massive black holes:
Fast-moving gas jets and gravitational forces equal to 10 billion suns compressed together
event horizon is an imaginary sphere around them
When matter enters the black hole, it increases in size - reaching other matter which it could not absorb before.
Types according to
physical properties
The Schwarzschild black hole, which has no charge, or rotation,
the simplest type of black hole that exists.
The Reissner -Nordstrom black hole, which does not rotate, but
which has electrical charge.
The Kerr-Newman black hole, which has charge and rotates.
The Kerr black hole, which rotates and does not have charge inside.
White holes and
Wormholes
White holes:
are not proved to exist considered to be the exact opposite of a black hole cannot absorb matter, it can only expulse considered by some physicists to be the mathematical answer to the general equations of relativity.
Wormholes:
combination of a black hole and a wormhole
would make matter enter through the black hole, and appear again through the white hole
too close to each other, spaghettification would not happen.
Parts of a Black Hole
The Singularity : all the mass of the black hole compressed in this very small space
Singularity has almost infinite density
The Event Horizon : defined as a big sphere surrounding the black hole
absorbs any material including light
Nothing can escape
Some theories say that only radiation can escape this area
The Accretion Disk: This is a disk that is composed by stellar material, which goes around
the black hole, forming a spiral.
The Ergosphere: If a black hole is rotating, as it spins, its mass causes the space and time
to rotate around it.
The Photon Sphere: place in which gravity is so high that photons have to travel around the
black holes´ orbit
light is forced to stay inside the black hole here
The Schwarzschild Radius: event horizon´s radius
the escape velocity is equal to the speed of light at this radius
Jets of Gas:
such high intensity that magnetic fields are emitted perpendicular to the accretiondisk
some charged particles go around the black hole forming jets of gases
Growth of a Black Hole
Once formed, it can continue to grow by absorbing additional matter
will continually absorb gas and interstellar dust from its direct surroundings and omnipresent cosmic background radiation.
Another possibility - merges with other objects such as stars or even other black holes
How Big Can A Black Hole Get?
no limit to how large a black hole can be
the largest black holes thought to be at the centers of many galaxies - masses equivalent to about a billion suns – radii as considerable fraction of radius of our solar system.
size of a black hole - defined by its mass
For a given mass - a length called the Schwarzschild radius proportional to the mass.
Falling into a Black Hole
Signals sent from the freely falling observer would be time dilated and red shifted.
Once inside the event horizon, no communication with the universe outside the event horizon is possible.
But incoming signals from external world can enter.
A black hole of mass M has exactly the same gravitational field as an ordinary mass M at large distances.
Falling into a black hole gravitational tidal forces pull space-time in such a way that time becomes infinitely long (as viewed by distant observer)
falling observer sees ordinary free fall in a finite time
Spagettification
In Astrophysics, this term refers to the effect a black hole imposes on a body or matter. The term was proposed by Stephen Hawkins in his book “A Brief History of Time”, where he compared this effect to spaghettis, saying that you are stretched, and you turn so thin that you break apart, and transform into matter.
There are so many black holes in the Universe that it is impossible to count them.
The Milky Way galaxy contains some 100 billion stars. The nearest one is some 1,600 light years from Earth. (1 ly=2.9 x 10^13 m)
The most massive known black hole in the universe has been discovered on 10 January 2008 by David Shiga.
The black hole is about six times as massive as the previous record holder and in fact weighs as much as a small galaxy.
How Many Black Holes Are There In The
Universe?
Conclusion
Individual modes may dominate the time evolution of some perturbation, and a whole set of them could be used to completely describe this time evolution.
When a black hole evaporates information is really gone.
Due to this there is trouble in energy conservation.
Invariance in time predictability.
Bibliography
The following websites were consulted for relevant information :
https://en.m.wikipedia.org/wiki/Black_hole
https://www.slideshare.net/mobile/GarethJenkins6/black-hole-presentation?qid=0be9e2dd-1af2-4e06-adf3-64d4d28dc320&v=&b=&from_search=8
https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-black-hole-58.html
https://www.encyclopedia.com/science-and-technology/astronomy-and-space-exploration/astonomy-general/black-hole
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