IN THE NAME OF ALLAH , THE IN THE NAME OF ALLAH , THE MOST GRACIOUS AND MERCIFULMOST GRACIOUS AND MERCIFUL

BLACK HOLESBLACK HOLES

ByBy

Rizwan AkberRizwan Akber03F-EE-5103F-EE-51

Sajjad HaiderSajjad Haider03F-EE-7603F-EE-76

IntroductionIntroduction

Black holes:

• BUT have been thought as far as the XVIIIth century…

• are until fascinating and mysterious!

Foundation of the study= Albert EINSTEIN’s Theory of General Relativity

four dimensionnal space:space-time

BLACKBLACK HOLESHOLES

OUTLINEOUTLINE

What is a black hole?What is a black hole?

Do BHs exist in Nature?Do BHs exist in Nature?– YES!YES!

What are the main classes of What are the main classes of black holes?black holes?

How do we try to detect the black holes?How do we try to detect the black holes?

Where are black holes found?Where are black holes found?

What is a black hole ?What is a black hole ?

2. Definition3. Structure of black holes

4. Properties and representations of black holes

1.1. HistoryHistory

1. History1. History

The concept of an object from which light The concept of an object from which light could not escape (e.g., black hole) was could not escape (e.g., black hole) was originally proposed by Pierre Simon Laplace originally proposed by Pierre Simon Laplace in 1795. Using Newton's Theory of in 1795. Using Newton's Theory of GravityGravity, , Laplace calculated that if an object were Laplace calculated that if an object were compressed into a small enough radius, compressed into a small enough radius, then the escape velocity of that object would then the escape velocity of that object would be faster than the speed of light be faster than the speed of light

• Schwarzschild found an exact solution to general relativity in 1916 that predicted black holes.

• Not much interest until the 30’s when supporting evidence is discovered

• Many great physicists since then have worked on black holes

1915: General Relativity, Einstein’s Theory of Gravity 1915: General Relativity, Einstein’s Theory of Gravity 1916: Schwarz child's Discovery of BHs in GR1916: Schwarz child's Discovery of BHs in GRBHs only understood & accepted in the 1960sBHs only understood & accepted in the 1960s

(Term “Black Hole” coined by John Wheeler in 1967) (Term “Black Hole” coined by John Wheeler in 1967)

Karl SchwarzschildAlbert Einstein

2. Definition2. Definition

Black holes = very massive bodies

speed of release at the surface > speed of light

light can’t escape from a black hole Black holes are hidden

3. Structure3. Structure

A black hole is divided into 2 main parts :

The SINGULARITY

= a little ball At the center of the black hole

•A few kilometres in diameter

•Matter inside is crushed to an infinite density

The IMMATERIAL SPHERE Around the singularity

= a zone of no return

• Nothing ( matter, radiations) can escape from black hole

• The boundary of this dark sphere is called the EVENT HORIZON

Structure of a black holeStructure of a black hole

4.Properties and representations4.Properties and representations

Black holes, unlike most objects can only have three characteristics

MassAngular momentum or spinElectric charge

To look for black holes formed by the death of high mass stars, we can look for binary systems that allows us to determine the mass of the objects. If we find an object with mass exceeding 3 M⊙ , but is neither a regular star, nor a neutron star, then we can argue that it may well be a black hole.

Black Holes: Do They Really Exist?Black Holes: Do They Really Exist?

We cannot see black holes directly, so we have to look for indirect evidences…

What would you look for to find a stellar-massed black hole, like those formed after the death of high mass stars?

Cygnus X-1

An x-ray source

What do we see?

A star (HDE 226868) - not a source for x-rays

Where do the x-rays come from?

HDE 226868 is in a binary system - orbiting something that is massive, but unseen!

Black hole classificationsBlack hole classifications

Black holes are theorized to come in Black holes are theorized to come in three different sizesthree different sizes– StellerSteller

– SupermassiveSupermassive

– PrimordialPrimordial

1. Stellar black holes1. Stellar black holes

One class of black-hole candidates are One class of black-hole candidates are stellar-mass black holes, which are thought stellar-mass black holes, which are thought to form when a massive star ends its life in a to form when a massive star ends its life in a supernova explosion. supernova explosion.

Created from stars of more than ~30 MCreated from stars of more than ~30 Msolarsolar

Detectable in binary systemsDetectable in binary systems

2. Supermassive black holes2. Supermassive black holes

A black hole is called A black hole is called SUPERMASSIVESUPERMASSIVE as as soon as its mass soon as its mass reaches several reaches several millions of times the millions of times the mass of our sunmass of our sun

Our galaxy : the MILKY WAY

Sagittarius constellation

Supermassive black holesSupermassive black holes

These are also called as quasi-stellar radio These are also called as quasi-stellar radio sources – quasars, for short – because they sources – quasars, for short – because they looked like stars, and produced large looked like stars, and produced large amounts of radio waves as well as light. amounts of radio waves as well as light.

Supermassive black holesSupermassive black holes

Credit: C.M. Urry & P. Padovani

Observations of supermassive Observations of supermassive black holesblack holes

Many galaxies have been observed to Many galaxies have been observed to contain such massive dark objects in contain such massive dark objects in their centers. their centers.

The masses of the cores of these The masses of the cores of these galaxies range from one million to galaxies range from one million to several billion times the mass of the several billion times the mass of the Sun. Sun.

3. Primordial black holes3. Primordial black holes

The existence of those The existence of those mini-black holes was mini-black holes was demonstrated by demonstrated by Stephen HawkingStephen Hawking

To take shape,they To take shape,they need:need:

high temperature

high pressure

How We Detect Black HolesHow We Detect Black Holes

Black holes and neutron stars don't give off Black holes and neutron stars don't give off light, so we can't just look for them. light, so we can't just look for them. However, astronomers can find black holes However, astronomers can find black holes and neutron stars by observing the and neutron stars by observing the gravitational effects on other objects nearby.gravitational effects on other objects nearby.

X-raysX-rays Rotating StarsRotating Stars Gravity LensesGravity Lenses

X-raysX-rays

Astronomers can discover some black holes and neutron Astronomers can discover some black holes and neutron stars because they are sources of x-rays. stars because they are sources of x-rays.

The intense gravity from a black hole or a neutron star will The intense gravity from a black hole or a neutron star will pull in dust particles from a surrounding cloud of dust or a pull in dust particles from a surrounding cloud of dust or a nearby star. nearby star.

As the particles speed up and heat up, they emit x-rays. So As the particles speed up and heat up, they emit x-rays. So the x-rays don't come directly from the black hole or the x-rays don't come directly from the black hole or neutron star, but from its effect on the dust around it. neutron star, but from its effect on the dust around it.

Although x-rays don't penetrate our atmosphere, Although x-rays don't penetrate our atmosphere, astronomers use satellites to observe x-ray sources in the astronomers use satellites to observe x-ray sources in the sky.sky.

Rotating starsRotating stars

Many stars rotate around each other, much as the Many stars rotate around each other, much as the planets orbit our Sun. When astronomers see a planets orbit our Sun. When astronomers see a star circling around something, but they cannot star circling around something, but they cannot see what that something is, they suspect a black see what that something is, they suspect a black hole or a neutron star.hole or a neutron star.

Gravity lensesGravity lenses

Astronomers use a technique called gravity Astronomers use a technique called gravity lensing to search for black holes and lensing to search for black holes and neutron stars. When a very massive object neutron stars. When a very massive object passes between a star and the earth, the passes between a star and the earth, the object acts like a lens and focuses light rays object acts like a lens and focuses light rays from the star on the Earth. This causes the from the star on the Earth. This causes the star to brighten.star to brighten.

Observations of black holesObservations of black holes

How can you check whether something is a How can you check whether something is a black hole or not? black hole or not?

The first thing you’d like to do is measure how The first thing you’d like to do is measure how much mass there is in that region. much mass there is in that region.

If you've found a large mass concentrated in a If you've found a large mass concentrated in a small volume, and if the mass is dark, then it's a small volume, and if the mass is dark, then it's a good guess that there's a black hole there. good guess that there's a black hole there.

Where are BHs Found?Where are BHs Found?

Centers of Galaxies Binary Stars

1 BIG BH per galaxymillion-billion x mass of sun

formation not fully understood

millions of ‘little’ BHs per galaxy ~ 10 x mass of sun

formed by collapse of a massive star

ConclusionConclusionAlthough they are allowed to tell us some characteristics of Although they are allowed to tell us some characteristics of

the black holes:the black holes:• dark dark • certainly present in each galaxycertainly present in each galaxy• composed with a singularity,accretion disk,event horizoncomposed with a singularity,accretion disk,event horizon• in rotation.in rotation.

Astrophysicists can only watch indirect proofs about their presence in the universe up to now.BHs are responsible for the most dramatic and energeticBHs are responsible for the most dramatic and energeticphenomena in the universe BHs are “seen” via the light phenomena in the universe BHs are “seen” via the light produced by infalling gas & via the gravitational pull that they produced by infalling gas & via the gravitational pull that they exert on nearby objectsexert on nearby objects

THE END!THE END!