Final Presentation Black Holes

8/3/2019 Final Presentation Black Holes

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ASTRONOMY CLUB

MANIPAL

PRESENTS

INTRODUCTION TO

BLACK HOLES


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Stars

Transition Animation

The idea of a body so massive that even light could not

escape was first put forward by geologist John Michell in

a letter written to Henry Cavendish in 1783 to the Royal

Society.

In 1915, Albert Einstein developed his general theory of

relativity.


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He showed that massive objects distort the four-dimensional

space-time continuum, and that it is this distortion that weperceive as gravity.

General Relativity


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Schwarzschild

He gave the first exact solution

ofEinstein's relativity

equations.

However, Schwarzschild

himself makes clear that he

believes that the theoretical

solution is physically

meaningless.


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He showed that bodies of sufficiently large mass would have anescape velocity exceeding the speed of light and so could not be

seen and these bodies are called Schwarzschild black holes.

Schwarzschild Theory

R=(2GM\c2)

This is known as Schwarzschild radius.


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Schwarzschild TheoryThe Schwarzschild radius of an object is proportional to the mass.

Accordingly, the Sun has a Schwarzschild radius of approximately

3 km, while the Earth's is only about 9 mm, the size of a peanut.

That is, if all the mass of the Sun (or Earth) were contained in asphere with a radius of 3 km (or 9 mm for the Earth), then the

volume of the Sun (or Earth) would continue to collapse into asingularity, due to the force of gravity.


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What is inside a black hole?

An animation.


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What is inside a black hole?

We cannot glimpse

what lies inside the

event horizon.

The simplest black

hole has mass but

neither charge nor

angular momentum.


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What is outside a black hole?

It is a boundary of zero thickness. Photons moving along tangents to sphere get trapped

in a circular orbit.


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Do they live forever ??

By using the laws of quantummechanics to study the region close to

a black hole horizon he proved that

black holes actually evaporate, slowly

returning their energy to the Universe.

Stephen William Hawking is a British theoretical physicist.

Born on 8 January 1942


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Black holes andThermodynamicsThe boundary of a black hole, has the property that it always

increases when additional matter or radiations falls into the

black hole.When two black holes collide or merge the resulting black hole is

larger in area than the individual sum of 2 black holes.


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Black holes andThermodynamics

These properties show a resemblance between area of eventhorizon of a black hole and the concept of entropy in

thermodynamics.

Law was derived relating change in mass of black hole to a

change in area of the event horizon.

Surface gravity as proportionality constant.


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The small change in theentropy is accompanied bychange in energy.

But black hole is created bygravitational collapse, itrapidly settles down tostationary state


It is characterized by only threeparameters: the mass, the

angular momentum, and the

electric charge.


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So by this concept if any radiation falls into a black hole will

be trapped and black hole will not emit any radiation.


But in 1974 to the great surprise of scientists it was found that black hole seemed toemit particles at steady rate.


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At that time it was confirmed that the whole of space is filled with pairs ofvirtual particles and antiparticles.

Their existence had been confirmed by small shift (the Lamb shift) theyproduce in the spectrum of light.



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Now, in the presence of black hole one member of a pair of virtualparticles may fall into the hole, leaving other member without a partner.

Where it appears to be as radiation emitted by the black hole.



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So as the black hole emits particles, its mass and size

steadily decreases.

Detailed calculations show that the emitted particle has

thermal spectrum corresponding to a temperature that

increases rapidly as the mass of the black hole decreases.


The emission will continue at an ever increasing rate until

eventually the black hole radiates itself out of existence.

So a primordial black hole should have almost completely

evaporated in the ten billion years that have elapsed since thebig bang, the beginning of the universe as we know it.


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The final stage of a

black hole would

proceed so rapidly

that it would end in

a tremendousexplosion.

Recently found star

explosion followed

by blackhole

explosion.

Animation by NASA.


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A black hole explosion would produce a massive outpouring of

high energy gamma rays.



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The big bang resembles a black hole explosion but on a vastly

larger scale.

So we hopes that an understanding of how black holes create

particles will lead to a similar understanding of how the big

bang created everything in the universe.



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Can a black hole bend light rays?

Einstein's theory of

general relativity

predicts that every

object bends light rays

through its gravity.

Light rays that pass a

little further away

don't get caught but do

get bent by the black

hole's gravity.


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Light rays that pass close to the black hole get

caught and cannot escape.


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This makes the star field appear distorted, and alsoproduces multiple images which is called gravitational

lensing.



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Since the particle emitted by a black hole come

from a region of which observer has very limited

knowledge.

We can predict is the probabilities that certain

particles will be emitted.


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THANK YOU!!


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A protostar is a large mass that forms by contraction out of the gas of a giant molecular

cloud in theinterstellar medium. The protostellar phase is anearly stage in the process of

star formation.

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P

rimordialblack

hole(hypothetical).

Primordial black

holes are of greatestinterest for

quantum effects.

These are formed

by the extremedensity of matter

present during the

universe's early

expansion.

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Final Presentation Black Holes