My presentation regarding the existence of Black Hole - the most interesting and controversial topic in the field of Astronomy and Astrophysics! Explore through my presentation! Hope you will like it! Enjoy reading!

1. “ Black Hole does not exists !!”
Name: Tamoghna Saha
Stream: Electronics and Communication Engineering

2. Contents
 Introduction
 Brief History of Black Hole
 Black Hole classification
 Event Horizon
 Black Hole Information Paradox
 Breaking News: “Black Hole does not exists !!”
 Think beyond Horizon !
 So what have we learnt ?

3. Among the various mysterious objects and
the phenomenon that are taking places in the
deepest part of our universe like supernovae,
hyper-novae, Quasar, Gamma ray Burst and
also the origin of the universe(it will be better
to use the term Multiverse), Black Hole is
one of the most important topic and intense
research field at present...

4. Brief History of Black Hole
 Black Hole is a region of space-time from which gravity prevents
anything, including light, from escaping. The theory of general relativity predicts
that a sufficiently compact mass will deform space-time to form a black
hole.
 Around a black hole, there is a mathematically defined surface called an
event horizon that marks the point of no return.
 The hole is called "black" because it absorbs all the light that hits the
horizon, reflecting nothing, just like a perfect black body in thermodynamics.
The first modern solution of general relativity that would characterize a
black hole was found by Karl Schwarzschild in 1916, although its
interpretation as a region of space from which nothing can escape was
first published by David Finkelstein in 1958.
 The discovery of neutron stars sparked interest in gravitationally collapsed
compact objects as a possible astrophysical reality.

5.  Black holes of stellar mass are expected to form when very massive stars
collapse at the end of their life cycle.
 Despite its invisible interior, the presence of a black hole can be inferred
through its interaction with other matter and with electromagnetic radiation
such as light. Matter falling onto a black hole can form an accretion disk
heated by friction, forming some of the brightest objects in the universe.
 By absorbing other stars and merging with other black holes, super-
massive black holes of millions of solar masses may form.
Black hole classifications
Class Mass Size
Super-massive black hole ~105–1010 Msun ~0.001–400 AU
Intermediate-mass black hole ~103 Msun ~103 km ≈ REarth
Stellar black hole ~10 Msun ~30 km
Micro black hole up to ~Mmoon up to ~0.1 mm

6.  Talking about super-massive black hole, we have one at the centre of
Milky Way.
 If there are other stars orbiting a black hole, their orbit can be used to
determine its mass and location.

7. Event Horizon
Far away from the black hole, a particle can move in any direction, as illustrated by the set of arrows. It is only restricted by
the speed of light.
Closer to the black hole, space-time starts to deform. There are more paths going towards the black hole than paths
moving away.
Inside of the event horizon, all paths bring the particle closer to the centre of the black hole. It is no longer possible for the
particle to escape.

8.  The defining feature of a black hole is the appearance of an event horizon.
 The event horizon is referred to as such because if an event occurs
within the boundary, information from that event cannot reach an outside
observer, making it impossible to determine if such an event occurred.
 As predicted by general relativity, the presence of a mass deforms space-
time in such a way that the paths taken by particles bend towards the
mass. At the event horizon of a black hole, this deformation becomes so strong that
there are no paths that lead away from the black hole.
 The shape of the event horizon of a black hole is always
approximately spherical.
 For non-rotating (static) black holes the geometry is
precisely spherical, while for rotating black holes the
sphere is somewhat oblate.
 The size of a black hole, as determined by the radius of
the event horizon, or Schwarzschild radius, is given by

9. BLACK HOLE INFORMATION PARADOX
The black hole information paradox results from the combination of quantum
mechanics and general relativity.
 It suggests that physical information could permanently disappear in a
black hole, allowing many physical states to devolve into the same state.
 This is controversial because it violates a commonly assumed tenet of
science—that in principle complete information about a physical system at
one point in time should determine its state at any other time.
 A fundamental postulate of quantum mechanics is that complete
information about a system is encoded in its wave function up to when the
wave function collapses.
 The evolution of the wave function is
determined by a unitary operator, and unitarily
implies that information is conserved in the
quantum sense. This is the strictest form of
determinism.

10. Breaking News: BLACK HOLE DOES NOT EXISTS !!
 “There is no escape from a black hole in classical theory, but
quantum theory enables energy and information to escape.”
 In a thought experiment, the researchers asked what
would happen to an astronaut unlucky enough to fall
into a black hole.
 In that picture, physicists had long assumed, the
astronaut would happily pass through the event horizon,
unaware of his or her impending doom, before gradually
being pulled inwards — stretched out along the way —
and eventually crushed at the 'singularity', the black
hole’s hypothetical infinitely dense core.
Stephen Hawking
 But on analysing the situation in detail, researchers team came to the
startling realization that the laws of quantum mechanics change the
situation completely. Quantum theory dictates that the event horizon must
actually be transformed into a highly energetic region, or 'firewall', that
would burn the astronaut to a crisp.

11. Beyond the horizon
 Hawking proposes a tantalizingly simple, option. Quantum mechanics
and general relativity remain intact, but black holes simply do not have an
event horizon to catch fire.
 The key to his claim is that quantum effects around the black hole cause space-time to
fluctuate too wildly for a sharp boundary surface to exist.
 In place of the event horizon, Hawking invokes an “apparent horizon”, a
surface along which light rays attempting to rush away from the black
hole’s core will be suspended.
 If more matter gets swallowed by the black hole, its event horizon will
swell and grow larger than the apparent horizon.
 Conversely, in the 1970s, Hawking also showed that black holes can
slowly shrink, spewing out 'Hawking radiation'. In that case, the event
horizon would, in theory, become smaller than the apparent horizon.

12.  Hawking’s new suggestion is that the apparent horizon is the real
boundary. “The absence of event horizons means that there are no black holes — in
the sense of regimes from which light can't escape to infinity,” Hawking writes.
 Although few accepts Hawking’s proposal that a black hole could exist
without an event horizon, they questions whether that alone is enough to get past
the firewall paradox. The presence of even an ephemeral apparent horizon
could well cause the same problems as does an event horizon.
 But unlike the event horizon, the apparent horizon can eventually dissolve.
 Although Hawking does not specify in his paper exactly how an apparent
horizon would disappear, researchers speculates that when it has shrunk
to a certain size, at which the effects of both quantum mechanics and gravity
combine, it is plausible that it could vanish. At that point, whatever was
once trapped within the black hole would be released (although not in
good shape).

13.  If Hawking is correct, there could be even no singularity at the core of
the black hole. Instead, matter would be only temporarily held behind the
apparent horizon, which would gradually move inward owing to the pull of
the black hole, but would never quite crunch down to the centre.
 Information about this matter would not be destroyed, but would be
highly scrambled so that, as it is released through Hawking radiation, it
would be in a vastly different form, making it almost impossible to work out what
the swallowed objects once were.

14. Thank You