INTRO...
Black holes and Mystery , they both are related to each other , whenever we think about the most mysterious objects of universe , the only answer we get or the image we get in our mind is a Dark Black round circle like thing which is revolving around its own path..Nobody knows from where they have come , and what are they made of . The only thing which we know is the formation of a Black hole . In my earlier post I told you about the formation and ending of a star in which I told you that when a heavy mass star dies it forms a black hole , so today I am going to explain black holes in more details...So lets go...
WHAT IS A BLACK HOLE...
So before starting the formation of black hole let us first know what is a black hole . A black hole can be defined as follows....
" A black hole is a region of spacetime , in which gravity of black hole prevents everything including light from escaping "
Black holes are present everywhere in this space . Black holes are actually like the monsters of our universe.
Those monsters which eat everything , means nothing can escape from black hole . Every object which enters into a black hole can not come back . No one knows where these go . The boundary of this black hole from where no one can escape is called "event horizon" . These black holes are said to be black as no light is being reflected from a black hole . Therefore it appears to be black .
They are almost invisible to see in space as they are black , therefore it is very difficult to find out a black hole . We have discovered black hole by the use different instruments to locate a black hole . For example these instruments detect how the stars close to a black hole react differently from other stars , which help us to detect a black hole .
FORMATION OF A BLACK HOLE...
Now we all know about what is a black hole? So now question arises how they are formed . It took a long time for the astronomers to find out how a black hole is formed . But finally the mystery was solved . Formation of a black hole takes place from the death of a heavy mass star . Having 10 times more mass than our sun . When they die , they form a black hole . Scientist think that the smallest black hole was formed when the universe was born .
The general theory of relativity states that sufficient compact mass is able to deform spacetime to form a black hole.
So basically the formation of a black hole can be described as follows....
When a star forms it starts to shine in the space with full freedom . It produces light and energy from nuclear fusion .Hydrogen combines to form helium , which releases a large amount of energy . This nuclear reaction produces an outward force which makes the star to cancel out the gravitational force which is present inside the star , which makes the star stable . So basically when all the fuel of a star is used for the nuclear fussion and all the hydrogen is converted into helium , then helium is converted into heavy elements like iron , copper and any more. So when these heavy elements are formed and the core of the star is filled up with these elements then the gravity of the star begin to increase as the mass increases .
So when the gravity increase it starts to attract the outer surface of the star to inwards . Because their is no force to stop this attraction as a result the matter of the star in the core starts to rush into each other . Which generates a huge amount of heat and energy . And at last the star explodes causing a "supernova" . The outer parts of the star spreads into the free space approaching the speed of light , whereas the inner core collapse due to its own weight . If the core remaining after the supernova is very massive (more than 2.5 times the mass of the Sun), no known repulsive force inside a star can push back hard enough to prevent gravity from completely collapsing the core into a black hole.
From the perspective of the collapsing star, the core compacts into a mathematical point with virtually zero volume, where it is said to have infinite density. This is called a singularity.Where this happens, it would require a velocity greater than the speed of light to escape the object's gravity. Since no object can reach a speed faster than light, no matter or radiation can escape. Anything, including light, that passes within the boundary of the black hole -- called the "event horizon" -- is trapped forever.
VIDEOS ON THE FORMATION OF BLACK HOLES ...... CLICK HERE....!!!!
SIZE OF A BLACK HOLE...
Now we have understood the formation of a black hole , that how are they formed and from what are they formed , full process of black hole formation . Now we should know how big are these black holes . Actually the size of a black hole is not fixed . There are many black holes in our universe , which all are of different sizes .
Basically black holes are in 4 different categories.They are....
Supermassive black hole.....
Supermassive black holes are the biggest giants of our universe . They are the biggest black holes of our universe. Their mass may vary bet 1000000 - 1000000000000 times the mass of sun . This is a huge amount . Actually think for a second means an object having this much times greater mass than our sun . We cannot even imagine . Not only this their size may be from 0.001–400 AU . This is also a huge amount .
Intermediate-mass black hole....
Intermediate-mass black hole are smaller than the above category but still are very big . Their mass can vary from 10000-10000 times the mass of our sun , and their size may be apprx. 1000 km .
Stellar black hole....
These are little much smaller than the above black holes. But are still bigger than our sun . Their mass may be apprx. 10 times the mass of our sun and their size may 30 km.
Micro black hole....
These are the smallest black holes of our universe . For these we can say that they are small . Their mass may be equal to our moon and their size can be 0.01 mm . You are thinking that they are so small then what disasters can they cause but you should not go to their size . They are small in their size but are very dangerous . Therefore we should not go on their size . Black holes are dangerous .
HISTORY OF DISCOVERY...
So now we have come to the history part . Basically history in the discovery of black holes . These black holes were first considered in 18 th century by John Michell and Pierre-Simon Laplace . The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although it was interpreted as a region of space from which nothing can escape was first published by David Finkelstein in 1958 .
The physicist "John Wheeler" coined the term "black hole" in 1967 . Before this black holes were termed as "dark stars" or "frozen stars" .
High-energy collisions...
Gravitational collapse is not the only process that could create black holes. In principle, black holes could be formed in high-energy collisions that achieve sufficient density. As of 2002, no such events have been detected, either directly or indirectly as a deficiency of the mass balance in particle accelerator experiments.This suggests that there must be a lower limit for the mass of black holes. Theoretically, this boundary is expected to lie around the Planck mass (mP = √ħc/G ≈ 1.2×1019 GeV/c2 ≈ 2.2×10−8 kg), where quantum effects are expected to invalidate the predictions of general relativity. This would put the creation of black holes firmly out of reach of any high-energy process occurring on or near the Earth.
However, certain developments in quantum gravity suggest that the Planck mass could be much lower: some braneworld scenarios for example put the boundary as low as 1 TeV/c2. This would make it conceivable for micro black holes to be created in the high-energy collisions that occur when cosmic rays hit the Earth's atmosphere, or possibly in the Large Hadron Collider at CERN. These theories are very speculative, and the creation of black holes in these processes is deemed unlikely by many specialists. Even if micro black holes could be formed, it is expected that they would evaporate in about 10−25 seconds, posing no threat to the Earth
SOME BLACK HOLE OF OUR UNIVERSE...
Cygnus X-1:
A stellar-mass black hole and x-ray source that lies some 6,500 light-years away. It is a binary system that contains a blue supergiant variable star and the x-ray source thought to be the black hole.
Sagittarius A*:
The supermassive black hole at the heart of the Milky Way Galaxy. It lies in the direction of the constellation Sagittarius. This black hole contains the mass of about 4 million suns.
M87:
This elliptical galaxy has a 3.5 billion solar-mass black hole at its heart. The black hole is surrounded by a disk of superheated material and has a jet of superheated material streaming away from the black hole that extends across 5,000 light-years from the galaxy’s core.
Centaurus A:
This galaxy, which lies in the direction of the constellation Centaurus, is a giant spiral galaxy with an incredibly active nucleus. It contains a 55 million solar-mass black hole at its heart, with two jets of material that stream away from the galaxy at about half the speed of light across a million light-years of space.
The most distant Black hole discovered is in the center of a quasar , named SDSS J1148 + 525.1 . Its mass has measured to apprx . equal to our sun . V4641 Sagittarii is the closest black hole to the earth , and has a distance of 1600 light years .
