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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