mad about physics sanjay

8/13/2019 Mad About Physics sanjay

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MA

A BRIEF HISTO

D ABOUT PHYSICS

Y OF SUPERMASSIVE BLACK

SANJAY KUMAR SHARMA

E-mail: [email protected]

HOLES
http://www.pdfonline.com/easypdf/?gad=CLjUiqcCEgjbNejkqKEugRjG27j-AyCw_-AP


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Introduction to Black HoleNeither the layman nor the specialists, in general, have any knowledge of the historical

circumstances underlying the genesis of the idea of the Black Hole. Essentially, almost all

the sundry simply take for granted the unsubstantiated allegations of some ostentatious

minority of the relativists. Unfortunately, that minority has been rather careless with the

truth and is quite averse to having its claims corrected, notwithstanding the documentaryevidence on the historical record.

On the basis of all theories about Black Hole some of the definitions are given as:

A Black Hole is a region of space whose gravity is so strong that it acts like a giant

vacuum cleaner in space. Anything that gets too close gets sucked in. When it hits the

centre, the singularity, it disappears forever. The gravity in black holes is so strong that it

tugs at space and time, slowing down time and stretching out space. Not even light, the

fastest thing in the universe, can escape from a black hole.

In General Relativity a black hole is so dense that nothing can escape from it, not even

light. General Relativity breaks down under such extremes so it cannot describe what goes

on inside a black hole. It is believed that a singularity exists inside and True Relativity alsoshows a singularity where the gravitational force becomes infinitely strong, but the physics

of the True Relativity does not end at the Schwarzschild radius or at the singularity.

Black holesAlmost everyone has heard of black holes. They occupy a special place in the public

imagination and rightfully so, for they are among the most exotic and interesting objects in

nature. However, what exactly are black holes, and how do we know they exist?

Perhaps the simplest and most intuitive definitions of a black hole is an object whose

gravity is so strong that nothing can escape, even at the speed of light. To understand this

better, we can consider the idea of escape velocity. Imagine we are standing on the earth

and throwing a ball up in the air. The faster the initial speed of the ball, the higher the ballwill go before it comes back down. Based on our understanding of gravity, as two objects

move apart the forces between them decreases proportional to the square of the distance.

So as we throw the ball higher and higher, the pull of gravity on the ball becomes weaker

and weaker, and we can imagine throwing the ball with such speed that it leaves the

gravitational field of the earth completely and flies far into space. The speed at which this

happens is called the escape velocity, for the Earth it is approximately 11km/s, which is

why we need such powerful rockets to launch vehicles into deep space.

The equation of gravity tells us that the escape velocity for a spherical object (such as a star

or planet) is given by. Thus, if we make an object more massive (larger M) or compress it

(smaller R), then we increase the escape velocity. Taking this to its extreme, we can imagine

taking an object as massive as the Sun and compressing it down to a radius of only 3km,which implies an enormous density (a teaspoonful of this material on Earth would weigh

many billions of tones!). This object would then be so massive and yet so small that the

escape velocity at its surface would be equal to speed of light. Since nothing in the Universe

can travel faster than speed of light, we infer that nothing can escape this objects strong

gravitational field. Such a remarkable entity is what we call black hole.

The concept of escape velocity gives us a clear and intuitive way of thinking about black

holes, but unfortunately does not provide a full description of the physics behind these

objects. For this we require a more complete description of gravity, which was provided by


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Einstein in his theory of general relativity in the early 20th

century. Einsteins remarkable

insight was that gravity is not simply a force between two objects that acts at a distance,

but instead represents a fundamental curvature in the fabric of space and time in the

universe. Massive objects curve the space-time around them, and the motion of objects

follows straight lines in this curved space, thus the Moon orbits the Earth because it is

following the curvature of space induced by the Earth's gravity. This is an extraordinary

idea, but it makes some robust predictions, chief among which is that light rays (whichhave no mass, and so traditionally were not thought to experience gravity) are deflected as

they pass close to the Sun. The observations of this effect provided among the first

experimental proof of Einsteins theory.

In light of general relativity, to fully understand black holes we must think of them as

objects for which the strong gravity bends space so much that even light cannot escape. In

this sense, black holes truly are black- if we could see a black hole directly; we would see a

black sphere, surrounded by images of background objects that had been deflected or

lenses by the strong gravity of the hole.

SECOND THEORY:

It has frequently been alleged by theoretical physicists that Newtons theory of gravitation

either predicts or adumbrates the black hole. This claim stems from a suggestion originallymade by John Michel in 1784 that if a body is sufficiently massive. All light emitted from

such a body would be made to return to it by its own power of gravity. The great French

scientist P.S. de Laplace made a similar conjecture in the eighteen century and undertook a

mathematical analysis of the matter.

However, contrary to popular and frequent expert opinion, the Michel- Laplace dark

body, as it is actually called, is not a black hole at all. The reason why is quite simple.

For a gravitating body we identify an escape velocity. This is the velocity that must be

achieved by an object to enable it to leave the surface of the host body and travel out to

infinity, where it comes to rest. Therefore, it will not fall back towards the host. It is said to

have escaped the host. At velocities lower than the escape velocity, the object will leave the

surface of the host, travel out to a finite distance where it momentarily comes to rest, and

then fall back to the host. Consequently, a suitable located observer will see the travelling

object twice, once on its journey outward and once on its returning way. If the initial

velocity is greater than or equal to escape velocity, an observer located outside the host,

anywhere on trajectory of the travelling object, will see the object once, and as it passes by

own its outward unidirectional journey. It escapes the host. Now, if the escape velocity is

the speed of light, this means that light can leave the host and travel out to infinity and

come to rest there. It escapes the host. Therefore, all observers located anywhere on the

trajectory will see the light once, as it passes by on its outward journey. However, if the

escape velocity is greater than the speed of light, then light will travel out to a finite

distance, momentarily come to rest, and fall back to the host, in which case a suitably

located observer will see the light twice. Furthermore, an observer located at a sufficiently

large and finite distance from the host will not see the light, because it does not reach him.

To such an observer the host is dark: a Michel-Laplace dark body. But this does not mean

that light cannot leave the surface of the host. It can, as testified by the closer observer.

Now, in the case of black hole, it is claimed by the relativists that no object and no light can

even leave the event horizon of the black hole. Therefore, an observer, no matter how close

to the event horizon, will see nothing.

Since about 1970 there has been an explosion in the number of people publishing technical

research papers, text-books and popular science books and articles on various aspects of


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General Relativity. A large proportion of this includes elements of the theory of black

holes. Quite a few are dedicated exclusively to the black hole. Not only is there now a

simple black hole with singularity, but also naked singularity, black holes without hair,

super massive black holes at the centre of galaxies, black hole quasars, black hole binary

system, colliding black holes, charged black holes, rotating black holes an even white holes!

Black holes are now seen everywhere by the astronomers, even though no one has ever

found an event horizon anywhere. Consequently, public opinion has been persuaded thatthe black hole is a fact of Nature and that anyone who questions the contention must be a

crackpot. It has become a rather lucrative business, this black hole.

Besides the purely mathematical errors that mitigate the black hole, there are also

considerable physical arguments against it, in addition to the fact that no event horizon has

ever been detected.

What does a material point mean? What meaning can there possibly be in the notion of a

material objects without any spatial extension? The term material point (or point mass) is

an oxymoron. Yet the black hole singularity is supposed to have mass and no extension.

Moreover, there is not a single shred of experimental evidence to even remotely suggest

that Nature makes material points. Even the electron has spatial extent, according to

experiment, and to quantum theory. A point is an abstraction, not a physical object. Inother words, a point is a purely mathematical object. Points and physical objects are

mutually exclusive by definition. No one has observed a point, and no one ever will because

it is unobservable, not being physical. Therefore, Nature does not make material points.

Consequently, the theoretical singularity of the black hole cannot be a point mass.

It takes an infinite amount of observer time for an object, or light, to reach the event

horizon irrespective of how far that observer is located from the horizon. Similarly, light

leaving the surface of a body undergoing gravitational collapse, at the instant that it passes

its event horizon, takes an infinite amount of observer time to reach an observer. However

far that observer is from the event horizon. Therefore, the black hole is undetectable to the

observer since he must wait an infinite amount of time to confirm the existence of an event

horizon. Such an object has no physical meaning for the observer. Furthermore, according

to the very same theoreticians, the Universe started with a Big Bang, and that theory gives

an alleged age of 14 billion years for the Universe. This is hardly enough time for the black

hole to form from the perspective of an external observer. Consequently, if the black holes

exist they must have been created at the instant of the Bang. They must be primordial

black holes. But that is inconsistent with the Bang itself, because matter at that time,

according to the Big Bang theoreticians, could not form lumps. Even so, they cannot be

detected by an external observer owing to the infinite time needed for confirmation of the

event horizon. This now raises serious suspicions as to the validity of the Big Bang, which is

just another outlandish theory, essentially based upon Friedmans expanding Universe

solution, not an established physical reality as the astronomers would have us believe,

despite the now commonplace alleged observations they adduce to support it. At first sight

it appears that the idea of a binary system consisting of two black holes, or a hole and a

star, and the claim that black holes can collide, are physical issues. However, this is not

quite right, notwithstanding that the theoreticians take them as well-defined physical

problems. Here are the reasons why these ideas are faulty. First, the black hole is allegedly

predicted by General Relativity. What the theoreticians routinely fail to state clearly is that

the black holes comes from a solution to Einsteins field equations when treating of the

problem of the motion of a test particle of negligible mass in the vicinity of a single


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gravitating body. The gravitational field of the test particle is considered too small to affect

the overall field and is therefore neglected.

It has been recently proved that the black hole and the expanding Universe are not

predicted by General Relativity at all in any circumstances. Since the Michel-Laplace dark

body is not a black hole either, there is no theoretical basis for it whatsoever.

Some interested questions related to Black Holes:

Que 1 How do black holes form ?Ans 1.The most common way for a black hole to form is probably in a supernova, an

exploding star. When a star with about 25 times the mass of the sun ends its life, it

explodes. The outer part of the star screams outward at high speed, but the inner part of

the star, its core, collapses down. If there is enough mass, the gravity of the collapsing core

will compress it so much that it can become a black hole. When its all over, the black hole

will have a few times the mass of the Sun. This is called a stellar-mass black hole, what

many astronomers think as a regular black hole.

2. We think that a black hole form when a very massive star collapses at the end of its

lifetime. Stars become like our sun because of energy from nuclear reactors going on deep

inside the star. They convert hydrogen to helium, and that gives off energy, which becomes

light. Once that hydrogen is used up, they can start using helium in their nuclear furnaces.But eventually any star will run out of fuel. Stars like our sun will collapse and become a

white dwarf. But very massive stars ten times heavier than our sun have such strong

gravity that when they collapse they cant stop. Everything in the star collapses to a tiny

point that still has the mass and gravity of the star but no longer shines. In fact the gravity

is so strong that even light cant escape. That is why we call it a black hole, if you could

visit a black hole (dont get too close!), you would probably see a black ball a few miles

across.

(An artist's impression of a black hole and its accretion disc, which occurs when large amounts of superheated gas and dust are torn off a

companion star (or left nearby the black hole after the star from whence it came perished), and rotates around the black hole at very fast

velocity).

Que 2 Can only stars become black holes, or could planets and other things become black

holes? If not, why is this ?Ans Technically anything can from a black hole, whether it is a star, a planet, or a human

being! In order for something to become a black hole, it has to be compressed so that its

smaller than its Schwarzschild radius. This radius is a distance from the centre of a star or

another object where math goes crazy (ones an object become a black hole, the

Schwarzschild radius can be called its event horizon. At this distance, space becomes

infinite, and time disappears). Mathematicians call this singular (this is where the word

singularity came from), Most of the time, this radius is much smaller than the object.


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The Schwarzschild radius of the Sun is three km. The formula for finding somethings

Schwarzschild radius is as follows:

R = 1.48 X 10-27 M (where M is the mass of the object in kg.)

Realistically, however, only stars naturally form black holes, and only stars that have more

than 3.2 times the mass of our Sun. Only through some strange supernatural or alien force

could you or I become a black hole, because we just dont have enough mass.

Que 3 What is the best evidence for the existence of black holes? Is it all really just atheory ?

Ans Astronomers have found a half dozen or so binary star systems (two stars orbiting

each other) where one of the stars is invisible, yet must be there since it pulls with enough

gravitational force on the other visible star to make that star orbit around their common

centre of gravity and the mass of the invisible star is considered greater than 3 to 5 solar

masses. Therefore these invisible stars are thought to be good candidate black holes. There

is also evidence that super massive black holes (about 1 billion solar masses) exist at the

centers of the many galaxies and quasars. In this latter case other explanations of the

output of energy by quasars are not as good as good as the explanation using a super

massive black hole.

Que 4 Can anything ever escape from a black hole ?Ans Nothing that falls into a black hole can come back out again at least not in its

original form. But a black hole may lose some of its mass. Quantum theory says that

virtual pairs of the particles sometimes wink into existence from the fabric of space itself.

These particles quickly cancel each other out and vanish. But if a pair of particles appears

just outside a black hole's horizon, one may fall inside, never to make it outside again. If

the one on the outside doesnt fall through the horizon, then the particles cant cancel each

other out. In essence, that steals a little bit of mass from a black hole. Over countless

billions of billions of years, the mass loss could become substantial enough to cause the

black hole to vaporize. Material would come out, but not in its original formonly as

energy and subatomic particles. This energy is known as Hawking radiation in honor of

Stephan Hawking, the physicist who first described it.

Que 5 How many black holes are there ?

Ans To use a technical term, gobs. Astronomers have discovered several dozen likely

super massive black holes in the cores of fairly nearby galaxies, plus many more in the

distant objects known as quasars. They have discovered perhaps a dozen or two likely

stellar-mass black holes in the Milky Way galaxy and a few possible intermediates-mass

black holes in the Milky Way and other galaxies. Yes these dont even qualify as the tip of

the iceberg more like a tiny ice chip. Super massive black holes may inhabit the cores of

all galaxies with central bulges of stars, and thousands of stellar-mass black holes may

inhabit the Milky Way, with thousands more in each of billions of other galaxies. One of

the goals of black-hole researchers is to find as many as possible so they can estimate how

common these objects are.

Que 6 How can a black holes own gravity, but not light, escapes from it ?

Ans In the case of the black hole, its best to think of gravity as Albert Einstein described

it: a warp in space time. Einsteins theory of special relativity says that mass warps the

space around it. For relatively lightweight bodies, like Earth, the effect is tiny. For heavier

objects, like the Sun, the effect is small but detectable. (Scientists confirmed the effect,

among other ways, by measuring the orbit of Mercury, the closest planet to the Sun, which

is dragged forward a bit by the Suns distortion of space-time.) And for the most massive

objects, like black holes, the effect is enormous. Diagrams in astronomy textbooks often


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depict black holes as deep wells in space-time, with matter funneling into the black hole

like pebbles dropped into water well on Earth. So nothing has to escape from the black

hole for it to exert a gravitational influence on the matter and space around it.

Que 7 How do black holes have energy if they form from dead or burned-out stars ?

Ans Black holes form from large stars that collapse when they run out of fuel for their

nuclear reactions. There are many forms of energy heat, light, energy of motion and the

energy of gravity. Black holes have LOTS of gravitational energy!Que 8 - Are there any black holes in our galaxy, and if so, are there any plans to explore

them ?

Ans- Fortunately for us there are no black holes near our solar system. Unfortunately this

means that we cant send a space probe to explore one. We believe that there are several

black holes in our galaxy. Some are about the size of stars. We can tell that a black hole is

there by how it affects a companion star. Of course we cant see the black hole its black!

But we can see that a star is going around in orbit around something else that we cant see,

and we cant see the gases that the black hole has sucked off from the other star. We also

think that most if not all galaxies have a big black hole at each centre. Our own Milky Way

probably has a big black hole at its centre, but its hard to tell for sure because there are

many stars in the way when we look towards the centre. Im not sure what would happento someone who went into a black hole, but I dont think it would be pleasant!

Que 9 - What is meant by the term associated with black holes called the event horizon?

Ans- Imagine a black hole and a beam of light passing by. The gravity of the black hole is

tugging on the light (and matter) nearby, but the beam of light has energy has energy so it

keeps trying to go on by. The gravity bends the light beam, but if light is not too close it can

still pass by the black hole. If it gets too close, the gravity of the black holes bends the light

into the hole and it cant escape. This would be true no matter what direction the light is

coming from around the hole. So there would be a sphere around the black hole where, if

light went in, it couldnt come out. That sphere is the event horizon. I guess its called

that because its the limit at which you could see an event occur, and a horizon is the limit

of which you can see (usually we mean the sky).

Que 10 How is time changed in a black holes ?

Ans Well, in a certain sense it is not changed at all. If you were entering a black hole, you

would find you watch ticking along the same rate as it always had (assuming both you and

watch survived the passage into the black hole). However, you would quickly fall towards

the centre where you would be killed by enormous tidal forces (e.g., the force of gravity at

your feet, if you fell feet first, would be much larger than at you head, and you would be

stretched apart).

Although your watch as seen by you would not change its ticking rate, just as in

special relativity someone else would see a different ticking rate on your watch than the

usual, and you would see their watch to be ticking at a different than normal rate. For

example, if you were to station yourself just outside a black hole, while you would find your

own watch ticking at the normal rate, you would see the watch of a friend at great distance

from the hole to be ticking at a much faster rate than yours. That friend would see his own

watch ticking at a normal rate, but see your watch to be ticking at a much slower rate.

Thus if you stayed just outside the black hole for a while, then went back to join your

friend, you would find that the friend had aged more than you had during your separation.

Second explanation In general relativity, time and space are a set of variables that can be

used to parameterize the geometry of space-time and the kinds of geodesics that are

possible. But they are not the only kinds of variables that form a set of four coordinates


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that span the dimensionality of space-time. In probing the mathematics of black holes,

physicists have discovered other sets of coordinates that are even better.

Que 11 If black holes are black, how can we find them ?

Ans The black hole itself may be invisible, but the ghostly fingers of its gravity leave

behind fingerprints. Some stars form in pairs, called binary systems, where the stars orbit

each other. Even if one of them becomes a black hole, they may remain in orbit around

each other. By carefully observing such a system, astronomers can measure the orbit of thenormal star and determine the mass of the black hole. Only a few binary systems have

black holes, though, you have to know which binaries to observe. Fortunately, astronomers

have discovered a signpost that points the way to black holes: X- rays.

If a black hole is eating matter from a companion star that matter gets very hot and emits

X- rays. This is like a signature identifying the source as a black hole. Thats why

astronomers want to build spacecraft equipped with special detectors that can see in X-

rays. In fact black holes are so good at emitting X- rays that many thousands can be

spotted this way. EXIST is one such spacecraft, designed to be able to detect tens of

thousands of black holes, some of which may be billions of light years away. EXIST will

create the most sensitive full sky map locating black holes, including those which may be

otherwise hidden from our view by obscuring gas and dust.Que 12 What happens when you fall into a black hole ?

Ans If you fall into a black hole, you are doomed. Sure, once you fall in you can never get

back out, but it turns out youll probably be dead before you get there.

The gravity you feel from an object gets stronger the closer you get. As you approach a

stellar-mass black hole feet-first, the force of gravity on your feet can be thousands of times

stronger than the force on your head! This has the effect of stretching you, pulling you

apart like taffy. Tongue-in-cheek, scientists call this spaghettification. By the time you

reach the black hole, youll be a thin stream of matter many miles long. It probably wont

hurt though: even falling from thousands of kilometers away, the entire gory episode will

be over in few milliseconds.

You may not even make it that far. Some black holes greedily gobble down matter, stealing

it from an orbiting companion star or, in the case of super massive black holes, from

surrounding gas clouds. As the matter falls in, it piles up into a disk just outside the hole.

Orbiting at huge speeds, the matter in this accretion disk gets extremely hot- even reaching

millions of degrees. It will spew out radiation, in particular high energy X- rays. Long

before the black hole could trip you apart youd be fried by the light.

But suppose you somehow manage to survive the trip in, what strange things await you on

your way down into forever?

Once you pass the point where the escape velocity is faster than light, you cant get out.

This region is called the event horizon. Thats because no information from inside can

escape, so any event inside is forever beyond our horizon.

If the black hole is rotating, chaos awaits you inside. Its a maelstrom as in falling matter

turns back on the incoming stream, crashing into you like water churning at the bottom of

a waterfall. At the very core of the black hole the seething matter finally collapses all the

way down to a point. When that happens our math fail us. Its as if the matter has

disappeared from the Universe, but its mass is still there. At the singularity, space and time

as we know then come to an end.

Que 13 How do black holes affect things near them ?

Ans Are we in danger of being gobbled up by a black hole? Actually, no. Were pretty

safe.


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The gravity from a black hole is only dangerous when youre very close to it. Surprisingly,

from a large distance, black hole gravity is no different than the gravity from a star with

the same mass. The strength of gravity depends on the mass of the object and your distance

from it. If the Sun were to become a black hole (dont worry its way too lightweight to ever

to do that), it would have to shrink so much that its event horizon would be only few miles

across. From the Earths distance of 150 million km wed feel exactly the same gravity as

we did when the Sun was a normal star. Thats because the mass didnt change, andneither did our distance from it. But if we got up close to the black hole, only a few

kilometers away, wed definitely feel the difference!

So stellar-mass black holes dont go around tearing up stars eating everything in sight.

Stars, gas, planets, and anything else would have to get up close and personal to a black

hole to get trapped. But space is big. The odds of that happening are pretty small.

Things are different near a super massive black hole in the centre of a galaxy. Every few

hundred thousand years, a star wanders too close to the black hole and gets torn apart.

This produces a blast of X-rays that can be visible for decades! Events like this have been

seen in other galaxies, and they are a prime target for satellites such as EXIST to reveal

otherwise dormant black holes.

Astronomers have found another amazing thing about galaxies: the stars in the inner partsof a galaxy orbit the galactic centre faster when the galaxys central super massive black

hole is more massive. Since those stars velocities are due to the mass in the inner part of

the galaxy and even a monster black hole is only a tiny fraction of that mass

astronomers conclude that the total mass of the inner region of a galaxy is proportional to

the mass of its central black hole! Its as if the formation of that black hole somehow

affected the formation of the billions of normal stars around it. EXIST will probe this

suspected feedback between galaxy formation and super massive black holes by

investigating black holes in a very large sample of galaxies.

Que 14 Can black holes be used to travel through space-time ?

Ans Its a science fiction clich to use black holes to travel through space. Dive into one,

the story goes, and you can pop out somewhere else in the Universe, having travelled

thousands of light years in the blink of an eye.

But thats fiction. In reality, this probably wont work. Black holes twist space and time, in

a sense punching a hole in the fabric of the Universe. There is a theory that if this happens,

a black hole can form a tunnel in space called a wormhole (because its like a tunnel

formed by a worm as it eats its way through an apple). If you enter a wormhole, youll pop

out someplace else far away, not needing to travel through the actual intervening distance.

While wormholes appear to be possible mathematically they would be violently unstable,

or need to be made of theoretical forms of matter which may not occur in nature. The

bottom line is that wormholes probably dont exist. When we invent interstellar travel,

well have to go the long way around.

Que 15 If a black hole existed, would it suck up all the matter in the Universe ?

Ans No. A black hole has a horizon which means a region from which you cant escape. If

you cross the horizon, you are doomed to eventually hit the singularity. But as long as you

stay outside the horizons, you can avoid getting sucked in. In fact, to someone well outside

of the horizon, the gravitational field surrounding a black hole is no different from the field

surrounding and any other object of the same mass. In other words, a one-solar-mass black

hole is no better than any other one-solar-mass object (such as, the Sun) at sucking in

distant objects.

Que 16 What if the Sun became a black hole ?


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Ans Well, first, let me assure you that the Sun has no intention of doing any such thing.

Only stars that weigh considerably more than the Sun end their lives as black holes. The

sun is going to stay roughly the way it is for another five billion years or so. Then it will go

through a brief phase as a giant star, during which time it will expand to engulf the planets

Mercury and Venus, and make life quite uncomfortable on Earth. After that, the Sun will

end its life by becoming a boring white dwarf star. If I were you, Id make plans to move

somewhere far away before any of this happens. I also wouldnt buy any of those 8-billionyear government bonds. But I digress. What if the Sun did become a black hole for some

reason? The main effect is that it would get very dark and very cold around here. The

Earth and other planets would not get sucked into the black hole; they would keep on

orbiting in exactly the same paths they follow right now. Why? Because the horizon of this

black hole would be very small only about 3 km and as we have observed as long as you

stay well outside the horizon, a black holes gravity is no stronger than that of any other

objects of the same mass.

Que 17 Are we in any danger of falling into a black hole ?

Ans No, although it is believed there is a super-massive black hole at the centre of our

galaxy, we are on the outside of our galaxy, on one of the spiral arms, quite far from the

massive monster.Que 18 Is a black hole really black?

Ans Not according to the British scientist Professor Stephen Hawking. He believes this

radiation can come from virtual particles, particles that are created out of nothing,

thereby defying the laws of physics. As pairs, they can then collide with one another and be

destroyed back into empty space. Normally, we would therefore never even see these

particles before they disappear. If a pair of these particles popped up at the edge of a black

hole, one could be sucked in while the other escaped as a newly created particle coming

from the black hole. This is known as Hawking radiation.

Que 19 Does a black hole ever fill up ?

Ans A black hole never literally fills up. However, a black holes life ends eventually as a

result of matter pouring in, As a result of losing energy and mass through Hawking

radiation, Professor Hawking suggests that there would come a point when the Hawking

predicts that the black hole might then explodes with a force of millions of hydrogen

bombs!

Que 20 Do black holes live forever ?

Ans Accordingly to Professor Hawking, no. He says that as a result of losing energy and

mass through Hawking radiation, there would come a point when the black hole no longer

has enough mass to completely curve the space around it, therefore ceasing to be a black

hole. Hawking predicts that the black holes might then explode with a force of millions of

hydrogen bombs!

Que 21 Is the edge to a black hole a smooth one, or is it a sharp boundary in space ?

Ans As seen from the vantage point of an outside observer, the edge is extremely sharp. It

is a mathematical perfect, spherical surface where light gets infinitely red shifted. To an

observer falling into the black hole, the boundary may be much more complicated than our

axi-symmetric mathematics would suggest. The horizon could be a turbulent surface

rippling with gravitational radiation, or it might dissolve into a fuzzy quantum state at

even finer scales of scrutiny. Someone falling into the horizon would experience NOTHING

PECULIAR, except that once they cross this mathematical surface by even one millimeter,

they can never turn back to escape the black hole. The event horizon is a most peculiar


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concept in physics. Still, it is a theoretical idea which needs to be studied with real data

before we can feel confident that we understand it.

Que 22 Why is it that black holes cant expand but the universe can ?

Ans They are two very different physical phenomena described by two very different sets

of equations in general relativity. The black hole solution is a singularity of the

gravitational field within a pre-existing, 4-d space-time. Black holes are embedded in space,

and there is a coordinate transformation which can be used to take you from the interior ofthe black hole inside the event horizon, to the external space outside the horizon. The Big

Bang solution has no external space in which it is embedded. The space defined by this

solution is a dynamic one which is always in a state of change as the universe expands or

collapses. It is like asking why apples are not bananas since they are both fruits

Que 23 How do astronomers study black holes when they cant see them ?

Ans We see them by their gravitational effects upon nearby stars which they are often

eating or causing to move at very high velocities just before they enter the black hole. A

star cluster that weigh 1 billion times the mass of the Sun, but only has 1 few million stars,

and has a very small volume producing lots of energy, is a prime candidate for a black hole.

Also, a binary star system where the total mass is 20 solar masses but the only visible star

has a mass of 2 solar masses means a dark companion with a mass of 18 solar masses. Inother words a black hole, we can see them, as the Hubble Space Telescope does, by the

intense core of light they produce in the centers of galaxies. When astronomers study the

speed of the gases in the cores of these galaxies, they find that the gases are orbiting faster

than is possible if only the identifiable stars are accounting for the mass. We can never see

them directly, but we can see what they do to the gas and stars around them. The above

image shows a titled dusty disk at the centre of a galaxy. The bright spot is the den of the

super-massive black hole.

Que 24 Could a galaxy ever collapse into a black hole ?

Ans Yes, at least theoretically. It would take a very long time, however. The stars move in

stable Keplerian orbits which could continue as they are for trillions of years. Long

after the stars they have burned out. But objects on elliptical orbits radiate gravitational

radiation, and eventually through the very weak leakage of gravitational energy away from

the orbiting stars, the orbits around the centre of galaxy begin to slowly drift inwards.

Eventually, the cold stellar cinders merge into one vest super-massive black hole and that

is the end of stellar matter in galaxies. The time this takes is enormoussomething like

10^150 years or more, so this end state is only relevant to galaxy evolution in an infinite

universe destined to expand forever. Sadly, this is the kind of universe we seem to be living

in!

Que 25 How does a black hole make room for all the stuff it sucks up ?

Ans It doesnt have to. It just gets bigger. The radius of a black hole is proportional to its

mass, so as it consumes stars and gas, its mass grows and so does its volume.

Que 26 If nothing can escape a black hole, why do they still emit x-rays ?

Ans It is true that once matter or energy passes within the so-called Event horizon of a

black hole that it can never turn around and get back out. However, in the real world, a lot

can happen to matter as it approaches the Event horizon. Commonly, matter falls into

what is called an accretion disk which orbits the black hole. Materials orbits the black hole

within this disk, but if it happens to be gas and dust, this matter experiences friction and

the disk heats up as some of the orbital energy of the gas is converted into heat. The closer

the disk material is to the black hole, the more rapidly it orbits so that the greater is the

heating effect. Just before it reaches the event horizon, this dark matter can be heated by


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friction to thousands of degrees which is enough to produce X-rays. Even higher

temperatures approaching a million degrees can occur which can produce gamma rays.

This disk radiation, being outside the black hole, is what we detect as we look at black

holes.

Que 27 What happens to matter when it falls into a black hole ?

Ans Outside the black hole, it depends on what form the matter takes. If it happens to be

in the form of gas that has been orbiting the black holes so called accretion disk, the mattergets heated to very high temperatures as the individual atoms collide with higher and

higher speed producing friction and heat. The closer the gas is to the black hole and its

Event Horizon, the more of the gravitational energy of the gas gets converted to kinetic

energy and heat. Eventually the atoms collide so violently that they get stripped of their

electrons and you then have plasma. All along, the gas emits light at higher and higher

energies, first as optical radiation, then ultraviolet and then X-rays and finally, just before

it passes across the Event Horizon, gamma rays. If the matter is inside a star that has been

gravitationally captured by the black hole, the orbit of the star may decrease due to the

emission of gravitational radiation over the course of billions of years. Eventually, the star

will pass so close to the black hole that its fate is decided by the mass of the black hole. If it

is a stellar-mass black hole, the tidal gravitational force of the black hole will deform thestar from a spherical ball, into a football-shaped object, and then eventually the difference

in the gravitational force between the side nearest the black hole, and the back side of the

star, will be so large that the star can no longer hold itself together. It will be

gravitationally shredded by the black hole, with the bulk of the stars mass going into an

accretion disk around the black hole. If the black hole has a mass of more than a billion

times of that of the Sun, the tidal gravitational forces of the black holes are weak enough

that the star may pass across the Event Horizon without being shredded. The star is

essentially eaten whole and the matter in the star does not produce a dramatic increase in

radiation before it enters the black hole. Once inside a black hole, beyond the Event

Horizon, we can only speculate what the fate of captured matter is. General relativity tells

us that there are two kinds of black holes; the kind that dont rotate and the kind that do.

Each of these kinds has a different anatomy inside the Event Horizon. For the non rotating

Schwarzschild black hole, there is no way for matter to avoid colliding with the

singularity. In terms of the time registered by a clock moving with this matter, it reaches

the singularity within a few micro seconds for a solar-massed black hole, and a few hours

for a super-massive black hole. We cant predict what happens at the singularity because

the theory says we reach a condition of infinite gravitational force.

Que 28 Do black hole really exist ?

Ans Probably. Astronomers have discovered quite a few objects that can only be

explained as black holes. These objects are dark, so we cannot see them, but they exert a

powerful influence on the stars, gas, and even space around them. These objects are so

dark, dense, and heavy that they must be either black holes or something even more exotic.

Que 29 Will our universe become a black hole ?

Ans Unlikely. Recent developments that show our universe is expanding at an even-

increasing rate. The cause of the expansion, called dark energy, is not understood, but it

appears that the universe is destined to undergo a slow and cold death. If there were

enough mass in the universe, and if dark energy did not exist, then it might have been

possible for the universe to collapse in on itself, condensing all matter and energy to an

almost infinitely small point, like a black hole.


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Que 30 Are any black holes close to Earth ?Ans The closest black holes yet discovered are several thousand light-years away. They

are so far that they have no effect on Earth or its environment. A super-massive black hole

appears to inhabit the centre of the Milky Way galaxy, about 27,000 light-years away.

Although it is several million times the mass of the Sun, its great distance insures that it

wont affect our solar system.

Que 31 Do black holes grow ?

Ans Yes they do! They grow up accreting matter that falls into them (it doesnt get

sucked into a black hole!). Stellar-mass black holes (black holes with the suns mass or

perhaps up to 50 times as much) can double their mass by accreting material from a

companion star. Super-massive black holes may grow by absorbing millions stars over the

course of billions of years.Que 32 How can gravity escape a black hole ?

Ans To observe outside the black hole, the gravitational field of a black hole escapes the

black hole not only because portions of the star are still outside the event horizon, but

because there is more to the gravitational field than just the part that is produced by

matter. The thing to always keep in mind with relativity is that there are always two

different observing frames in any relativistic process. For the black hole, an observer at

great distances will see one thing happen, and an observer actually falling into the black

hole will see something quite different. Suppose the person falling in, emitted regular

electromagnetic pulses during the whole trip. In her reference frame, nothing strange was

happening, except that once she crossed that invisible, mathematical surface called the

event horizon, she would then be snuffed out of existence within the few milli seconds ittakes to fall from there and into the singularity.

Que 33 If a black holes pull is faster than the expansion of the universe, will a new Big

Bang happen ?

Ans - What you are asking is, could the gravitational pull from a single black hole

overwhelm the expansion of the universe and send it into collapse. To do this, the mass

inside the black hole would have to equal the mass outside of it in order for the

gravitational field to be cosmologically important. If you have a black hole that has the

mass of the universe, you already do not have a universe that is expanding. The material


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would be dragged into the black hole before it could get very far away, and this condition

would have to have taken place when the universe was very young. Now according to

physicists such as Stephan Hawking, it may be possible that matter flowing into a black

hole could form a separate universe in another part of our space-time, or even in another

dimension. We have no way to know if this is possible but in that case a black hole could

form another Big Bang in a separate universe. This is all speculation, and makes for good

science fiction but not much else.

Que 34 What happen when black holes collide ?

Ans There is no hing to prevent two black holes from orbiting each other just as the

Moon orbits earth. So long as they are at a distance of a few dozen time; their event

horizon, they can orbit each other for a very long time. If they are much closer, then

gravitational forces deform them into football like shapes and they start to emit gravity

waves in huge amounts. This causes the orbits to evolve and decay rapidly so that the black

holes eventually merge together. The Chandra X-ray observatory recently discovered two,

super-massive black holes in the core of the galaxy NGC 6240 in the last stages of this

million-year death spiral. A team of astronomers led by Stefanie Komossa at the Max-

Planck Institute announced this discovery in November 2002. At the present time, the two

black holes are 3000 light years apart, but within a few hundred million years, there willonly exist one, even more stupendous black hole. In another galaxy called Arp 220, a

similar pair of super-massive black holes has also been spotted by Chandra. Astronomer

David Clements at the Imperial College London and his colleagues announced this finding

in April 2002. This galaxy is well known to astronomers as one of the most powerful

infrared galaxies in the universe. The bottom line is that when two black holes collide and

merge, they emit huge amounts of gravitational radiation. This energy is lost to the black

holes, and causes the black hole system to lose about five percent of its mass in the process

of formation.

Que 35 What is the Singing Black Hole ?

Ans Astronomers have known since the 1970s that the X-ray light produced by some

black holes isnt steady in intensity. It actually flickers at many different times, from

milliseconds to several seconds. Astronomers call some of the more regular of these flicking

quasi-periodic oscillations or QPOs. If the process producing this flickering were

completely random, every frequency of flickering should be present with about the same

intensity, like the hiss you hear on a blank recording tape. But this turns out not to be the

case. Instead for some black holes, slower flickering is more common that fast flickering,

and in a particular way called one over f noise. What this jargon means is that whatever

is going on in regions closest to a black holes horizon, it has some kind of memory or

correlation. Astronomers Phil Utley and Lane McHardy of the University of

Southampton have analyzed this flicker noise and now conclude that it has a common

cause among a vast number of different black hole systems. They have used the NASA,

Rossi X-ray Timing Explorer satellite for the last six years, listening-in to the X-ray sounds

from a variety of black holes. What they think they are hearing is astonishing. Near the

inner edge of an accretion disk, gases are turbulent and form cells of plasma. When these

plasma cells of varying size pass across the black hole horizon, they emit a burst of X-rays.

When added together, the X-ray light from these gas cells produce the one over f noise

that is detected by the NASA Rossi XTE satellite. What is even stranger is that the same

black hole will suddenly change its style of making this noise. This kind of noise is also

interesting because if you took classical, popular or jazz music and counted its frequency

content in the same way, it would produce a similar flicker noise. So, although we may not


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identify the tune, black holes do have a song to sing, and like whales in the ocean, they

change their song from time to time. Even more surprising is that super-massive black

holes in the cores of distant galaxies also produce this same kind of noise, but slowed down

a million times. The conclusion is that stellar and super-massive black holes lead to exactly

the same observations and accretion disk physics once the differences in their masses are

factored out.

Que - 36 We see black hole, e.g. the one in M87. Does this preclude the idea that universe isa black hole, or could one black hole exist inside another black hole ?

Ans Actually a black hole could exist inside a black hole. Imagine turning a whole galaxy

into a black hole by bringing all its stars extremely close together. All these stars might

themselves be black holes. The individual black holes wont even be touching when they are

all surrounded by a larger event horizon with a radius corresponding to the mass of the

galaxy. However, once they are all surrounded by a larger event horizon with a radius

corresponding to the mass of the galaxy. However, once they are all within the event

horizon they will end up merging together in a final collapse together in a final collapse to a

singularity.

Que 37 Can black holes be used to explain the missing mass in the universe ?

Ans Black holes would be hard to detect, and a great deal of unseen mass could be storedinside black holes. However, based on how we think black holes must form (from

collapsing cores of relatively rare super-massive stars) there cant be that many black holes

in comparison to more normal stars. Hence we expect that the total mass in black holes is

only a small fraction of the mass we can see, so that they dont constitute a major

component of the unseen, or missing mass in the universe.

Que 38 Is it possible that there is a black hole in our galaxy ?

Ans It is almost certain that there are black holes in binary systems in our galaxy.

Another question is whether or not there is a really big black hole in the centre of our

galaxy. In recent years the answer has emerged; yes! Direct observations of the centre of

the galaxy have been able to follow the orbits of the massive stars over a number of years.

Using Keplers laws we can calculate the mass of the thing that they are orbiting and it

comes out to about 3 million solar masses. Thus, although we dont directly observe the

black hole, we see the effect of gravitational field.

Que 39 What is a white hole ?

Ans The equation of general relativity have an interesting mathematical property; they

are symmetric in time. That means that you can take any solution to the equations and

imagine that time flows backwards rather than forwards, and youll get another valid

solution to the equations. If you apply this rule to the solution that describes black holes,

you get an object known as a white hole. Since a black hole is a region of the space from

which nothing can escape, the time reversed version of a black hole is a region of space into

which nothing can fall. In fact, just as a black hole can only suck things in, a white hole can

only spit things out. White holes are a perfectly valid mathematical solution to the

equations of general relativity, but that doesnt mean they actually exist in nature. In fact,

they almost certainly do not exist, since theres no way to produce one. (Producing a white

hole is just as impossible as destroying a black hole since the two processes are time

reversals of each other.)

Que 40 What is a wormhole ?

Ans So far, we have only considered ordinary vanilla black holes. Specifically, we have

been talking all along about black holes that are not rotating and have no electric charge. If

we consider black holes that rotate or have charge things get more complicated. In


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particular, it is possible to fall into such a black hole and not hit the singularity. In effect,

the interior of a charged or rotating black hole can join up with a corresponding white

hole in such a way that you can fall into the black hole and pop out of the white hole. This

combination of black and white holes is called a wormhole. The white hole may be

somewhere very far away from the black hole indeed; it may even be a different Universe--

--that is, a region of space-time that aside from the wormhole itself is completely

disconnected from our own region. A conveniently located wormhole would thereforeprovide a convenient and rapid way to travel very large distances or even to travel to

another universe, may be exist to the wormhole would lie in the past, so that you could

travel back in time by going through. All in all they sound pretty cool but before you apply

for that research grant to go search for them, there are a couple of things you should know.

First of all, wormholes almost certainly do not exist. As we said above in the section of

white holes, just because something is a valid mathematical solution to the equations

doesnt mean that is actually exists in nature. In particular, black holes that form from the

collapse of ordinary matter do not form wormholes. Furthermore even if a wormhole were

formed, it is thought that it would not stable. Even the slightest perturbation would cause it

to collapse. Finally even if wormholes exist and stable, they are quite unpleasant to travel

through. Radiation that pours into the wormhole gets blue shifted to very high frequencies.As you try to pass through the wormhole, you will get fried by these X-rays and gamma

rays.

Que 41 Can black holes be used to travel through space-time ?

Ans Its a science fiction clich to use black hole to travel through space. Dive into one,

the story goes, and you can pop out somewhere else in the Universe, having traveled

thousands of light years in the blink of eye.

But thats fiction. In reality, this probably wont work. Black hole twist space and time, in

a sense punching a hole in the fabric of the Universe. There is a theory that if this happens,

a black hole can form a tunnel in space called a wormhole (because its like a tunnel

formed by a worm as it eats its way through an apple). If you enter a wormhole, youll pop

out someplace else far away, not needing to travel through the actual intervening distance.

While wormholes appear to be possible mathematically, they would be violently unstable,

or need to be made of theoretical forms of matter which may not occur in nature. The

bottom line is that wormholes probably dont exist. When we invent inter-stellar travel,

well have to go the long way around.

ABOUT EXIST

The Energetic X-ray Imaging Survey Telescope (EXIST) is a proposed NASA

Satellite that will look at the energetic X-rays emitted from black holes and other exotic

astronomical objects. It is a strong candidate to be the Black Hole Finder Probe, one of the

three Einstein Probes in NASAs Beyond Einstein program. EXIST could be launched

early in the next decade, and with unparalleled sensitivity, will be used to study black holes

of all sizes.


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Recapitulation and Conclusion The black hole and the Big Bang model are mutually exclusive. The black hole has no valid

basis in General Relativity or Newtons theory of gravitation. The alleged escape velocity of

a black hole and the radius of its event horizon (Schwarzschild radius) are obtained from

Newtons expression for escape velocity which is inserted post hoc into Hilberts solution in

order to obtain a material source: this is a two body relation in what is alleged to be the

solution for a one body problem, and so it is inadmissible. The idea of multiple black holesviolates the defining boundary condition of space-time asymptotic flatness of the alleged

black hole, which necessarily excludes the possibility of multiple black holes. The principle

of Superposition is invalid in General Relativity and so additional masses and radiation

cannot be superposed upon any solution to Einsteins field equations in order to obtain

multiple masses and photons. When there are no materials sources present for the

gravitational field Einsteins field equations must vanish. The total energy of Einsteins

gravitational field is always zero so that Einsteins field equations violate the usual

conservation of energy and momentum and cannot localize energy to produce Einstein

gravitational waves. Einsteins pseudo tensor representing the energy of the gravitational

field is a meaningless collection of mathematical symbols because it implies the existence of

a 1

st

order intrinsic differential invariant which does not in fact exist. The HawkingPenrose Singularity Theorem is invalid. The cosmological constant has no physical

meaning and so expansion of the Universe.

It was once told as a good joke upon a Mathematician that the poor man wentMad and mistook his symbols for realities; As M for the moon and S for the Sun OLIVER HEAVISIDE (1893)

mad about physics sanjay

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