There
is no doubt or disagreement that the ‘Black Hole’ is one of the most talked
about and enigmatic aspects of space exploration. Scientists have been
researching this subject for many years and even decades. Today we will try to
know a little bit about this subject.
The
subject was first highlighted in 1784 by the English clergyman John Mitchell.
He identified this celestial object as a 'Dark star' and later as a
'Gravitationally Collapsed Object'. This idea was later supported by the
mathematician Pierre Simon Laplace. The term black hole was probably first used
by the American astronomer Robert Dicke. The word was first printed in 1963 by
journalist Ann Ewing in her article. A few days later, in a lecture by
scientist John Wheeler, a young student suggested the use of the word 'Black
Hole', and scientist Wheeler accepted it, and the use of the word 'Black Hole'
has increased since then. So many give credit to John Wheeler for introducing
the word Black Hole'.
A
black hole is a dark region whose very strong force of attraction attracts any
object, even electromagnetic waves (light). Einstein's 'Law of General
Relativity' states that what we perceive as a gravitational force is actually
obtained from the curvature of space and time. According to that theory of
relativity, a large amount of mass condenses together to form this black hole.
John Mitchell was the first to say through his mathematical method that the
escape velocity of a black hole must be greater than the speed of light. (Escape
Velocity: The minimum speed required to get out of the gravitational
force of a cosmic object.) Of course, John Mitchell also said about one and
an half hundred years ago that in order to identify the black hole, one must
analyze its gravitational effect on the surrounding objects of the black hole,
which is accepted today as a recognized method.
Now
we will try to understand how this black hole is actually created. Hydrogen
acts as the fuel for any major star. This hydrogen produces helium through the
process of nuclear fusion, which in turn produces light energy and heat energy
and radiates. Thus, after hundreds of billions of runs, when hydrogen is
depleted, the process of atomic addition of helium begins and it produces
carbon. Then in this way neon, oxygen and silicon are produced respectively and
finally iron is produced. This iron is a very strong, compact and stable
substance. So after that the process of nuclear fusion is completely stopped
and as a result the process of heat and light energy production also comes to a
standstill. In this case the mass of the star increases drastically and the
force of gravity also increases. A star is stable as long as the value of
radiation as the Centrifugal force and gravitational force as its inverse
Centripetal force is equal. This stable state is called the
Tolman-Oppenheimer-Volkoff Limit. The center of the star is broken by a massive
cosmic explosion when the amount of gravitational force inside the star
increases further and the value of the equilibrium of the star's interior
exceeds the Tolman-Oppenheimer-Volkoff limit. This phenomenon is called Supernova
explosion.
After
this explosion, most of the parts of stars spread far and wide in different
parts of space. Here the remnants of a star can pass through two states and it
depends on the mass of that state. Indian scientist S. Chandrasekhar explains
what can happen in any situation. This system is called Chandrasekhar Limit in
recognition of Chandrasekhar's work. If the mass of the remaining stars is
equal to or greater than 2.17 times the mass of the Sun, then the remnants of
that star will inevitably end up in the black hole. Not only is the black hole
created in this way, but the huge amount of gas that was in dense condition in
the universe right after the Big Bang came together and formed the black hole.
Later, under the influence of their attraction, more gas, dust and even small
black holes came and increased the size of these black holes, creating
extremely heavy black holes known as Super Massive Black Hole which are usually
in the center of a galaxy. For example, at the centre of our Milky Way galaxy
is Sagittarius A*. Apart from this, collisions of high energy and
high speed objects can also cause black holes. For example, a man-made
experiment on earth can be mentioned here. Deep inside the ground near Geneva,
Switzerland, CERN's Large Hadron Collider created a black hole-like situation
after collision of two objects.
There
are four types of the black hole, based on its size. Black holes with a mass of
105-1010 times the mass of the sun is called Super Massive
Black Hole, a mass between103-104 times that of sun is
called Intermediate Mass Black Hole, and a mass of stars between 2.17-102 of
that of sun is called Stellar Black Hole and those whose mass is equal to the
mass of the moon are called the Micro Black Hole. However, the last mentioned
black hole persisted only for a short
time after the Big Bang and now does not exist at present except theoretically.
Again,
there are four types of black holes based on rotation and electric charge.
Non-rotating, charged black hole is called Reissner-Nordstrom-Metric Black
Hole, rotating, non-charged black hole is called Ker-Metric Black Hole,
non-rotating, non-charged black hole to Schwarzschild Black Hole and rotating,
charged black hole is called Merr-Newman-Metric Black Hole. We understand this
last to mean black holes because they are so many in numbers.
If we talk about the structure of the black hole, then it can
be seen that it consists of several parts. The central part of the black hole
is called Singularity. According to Einstein's theory of relativity, the centre
is a place where the curvature of time and matter, in the three-dimensional
universe, is infinite. In a non-rotating black hole, the position of the
singularity is like a point, but in a rotating black hole, its position is like
a ring. In both cases, however, all the mass of the black hole is concentrated
in this volume less space, and the value of its density is infinite. When an
object moves under a black hole, it first disintegrates as it moves into
infinite density and then turns into smaller parts, eventually merging with the
singularity of the black hole. This phenomenon is called ‘Noodle Effect’.
The
functional part of the ring centered on the singularity of the black hole,
after which no object can return out of the black hole, is called the ‘Schwarzschild
Radius’. The 'Event Horizon' is marked as the boundary of the functional part of
the black hole where this Schwarzschild radius ends. Although the Event Horizon
of the non-rotating black hole is completely round where as the Event Horizon
of the rotating black hole is oblate. But in reality, the Event Horizon of a
black hole is a hypothetical boundary line, so it is never possible to
determine such a boundary depending on the size of a black hole. The reason for
naming Event Horizon is that it is not yet possible to know the full details of
the events that took place on that side of the border.
Another
ring has been found to be about 1.5 times the distance from the Singularity to
the Event Horizon, which is made up of zero-density photon particles. (Photon:
The smallest isolated part of an electromagnetic wave or light) This
photon is orbitally located around a black hole. If a ray of light passes
through this photon ring, then that light travels towards the black hole at a
faster speed.
The
area around the black hole from which the objects lose control and move towards
the black hole little by little, means that the intensity of the black hole is
first felt after coming to the area where the object changes its position and
moves towards the black hole is called Ergosphere. When an object moves into
the Ergosphere, it can return to its previous position. Of course it will
require extra energy for the object. However, if this event occurs in the polar
region of the black hole, then the object will not be able to return in any way
because the Ergosphere in the polar region merges perfectly with the Event
Horizon. Again, if this happens in the equatorial region, then the least energy
must be applied to the object because the expansion of the Ergosphere is the
greatest in this region, that is, the distance from the black hole to the edge
of the Ergosphere is the greatest here.
There
is another small region after this Ergosphere and this is the last outer area
of the black hole. This part is called the Innermost Stable Circular Orbit or
ISCB. In this region, an object can move around the black hole in a steady
manner. Its location depends on the nature of the black hole. However, current
scientists are still quite skeptical about the structure of the black hole.
Einstein himself expressed doubts about this.
We
cannot see the formation of the black hole. There are basically two reasons for
this. First, the attraction of the black hole stops the time because there is a
direct relationship between the velocity of light and time. If it is possible
for us to observe the events inside the black hole, we would see that
everything there was moving at a very slow pace. Again, if it is possible to
observe the rest of the universe from inside the black hole, we would see
everything moving very fast. This phenomenon is called Gravitational Time Dilation.
Nothing can be observed for this infinite delay. Second, since light is
absorbed by the black hole, we will see that the light will begin to fade after
the star collapse and eventually disappear into the black hole. No information
will reach us from there.
The
black hole is a very mysterious unknown world to us because it is a place where
the laws or formulas of physics do not work, so all the events inside it are
still incomprehensible to us today. Scientists say that all the measurable
information inside the black hole is lost forever. This phenomenon is called
Information Loss Paradox. However, from the position around the black hole,
scientists speculate that if the black hole is formed after stabilization,
three types of features may occur in it. These are firstly, the mass-centered
property secondly, the electric-centered property and finally, the
angular-momentum-related property. (Angular-momentum: A special
feature of physics produced by the rotation of a rotating object) Of
course, this assumption is subject to extensive research.
There
are several things that can be said to be obtained by observing the black hole.
On 10th April 2019, a blurry picture of the black hole was first published in
front of the people of the world. This was done through a worldwide network of
radio telescopes called Event Horizon Telescopes. This black hole is the black
hole at the center of the M-87 galaxy or Virgo galaxy, 55,000,000 light-years
from Earth, whose mass is 650 crore times the mass of the sun. Here the
existence of the black hole is understood due to the curvature of the lines of
light near the event horizon of the black hole. Using this same technology, the
magnetic field was discovered outside the event horizon of the Sagittarius A*
black hole at the center of our galaxy, 25,640 light-years from Earth in 2015.
In addition, the gravitational waves that were generated when the two black
holes merged on 14th September of that year were observed for the first time.
The mass of the two black holes that merged here is 36 times and 29 times the
mass of the sun respectively. This is the greatest proof of the presence of a
black hole.
As
for the black hole in the center of our galaxy, the mass of this Sagittarius A*
black hole is equal to 4.3 X 106 times the mass of our sun and a little
less than 0.02 light-years in diameter. This type of super massive black hole
is present in the centre of all galaxies. However, if the mass is taken into
account in per unit area, then it can be seen that the mass of the stellar
black hole is always greater than that of this type of black hole.
In
1974, the famous British scientist Sir Stephen Hawking said that the black hole
is not completely dark but emits even a small amount of heat radiation which we
call Hawking Radiation which is still widely studied by many scientists around
the world. In other words, the energy required for this light and heat
radiation is provided by the black hole itself. According to Einstein's
mass-energy equation (E=mc2), mass and energy are interrelated, so
energy loss means that the mass of the black hole decreases little by little.
In this way, the black hole will disappear into space. The temperature we are
talking about here is called Hawking Temperature. This temperature is 62 nano
Kelvin or -273.15 degree Celsius in the case of black hole like the Sun. This
temperature is inversely proportional to the mass of the black hole and
proportional to the surface gravity, i.e. the smaller black hole radiates more
than the larger one. If this theory is proven, then it can be said that the
black hole is gradually evaporating as it compresses with increasing heat
radiation. However, the radiation level in the black hole is so low that it is
virtually impossible to detect them from earth. However, through mathematical
analysis, scientists speculate that an explosion with gamma ray may happen at
the end of this process, which may help in the future. In this context, the
Fermi Gamma Ray Space Telescope has launched in 2008 for further observation
and research.
If
the light of all the stars in the sky could be obscured in any way, then a
glimmer of bright red light could be seen spread all over the sky. This ray of
light is the last radiant ray produced after the Big Bang, called Cosmic
Microwave Background Radiation. The temperature of this radiation is 2.7 Kelvin
or -270.45 degree Celsius. If the radiated temperature of the black hole would
be higher than this, it would take 1064 years for the black hole
equal to the sun to completely evaporate. In the case of a huge black hole, it
will take more time. Although not proven, no second radiation other than
Hawking radiation has yet been reported, so indirect observation is more
relevant than direct observation for black hole observation.
However, it is not yet
possible to say exactly what happens after that. A group of that White Holes,
Warm Holes may be created through black holes. Another group of scientists says
that it will be possible to reach another universe by Time-Travel through the
black hole, that is, Multi-verse Theory or Parallel-Universe Hypothesis may be
clearly and accurately established in near or far future through the black
hole. With the help of modern technology, we may inform our existence in future
to new universe through black hole. Another group of scientists claimed that when
black hole will come to an end, its mass and material will also facilitate the scientists
say birth of new stars. However, there is no doubt that the subject is complex
enough and researchable. The only answer lies within the hand of highly
advanced technology and research of the future.
