What is a Black Hole?

1
What is a Black Hole?
? This is an object with a gravitational field so
powerful that even electromagnetic radiation
(such as light) cannot escape its pull.
2
An easily understandable explanation
? An understandable tennis ball example. ?
Body/volume/gravitational attraction
3
How do Black Holes come to be?
? Formation of a neutron star ? The mass limit
that is needed for a Black Hole to appear -
achievable ? Due to the large number of
identified neutron stars, and the relatively
frequent Supernovas, Black Holes must have
appeared
4
What does it take to be a Black Hole?
? Newton's shell theorem
? The gravitational pull between two objects
5
What does it take to be a Black Hole? (continued)
? Why do the stars shine and why are they not
Black Holes?
? Black Holes have similar mass but
6
Sizes of Black Holes
? Supermassive Black Holes ? Intermediate-mass
Black Holes ? Stellar-mass Black Holes
? Small Black Holes ? Micro Black Holes
7
Sizes of Black Holes (continued)
Sizes of Black Holes (continued)
? Micro black holes may theoretically be
produced by

1) The Big Bang 2)
Powerful particle accelerators ? The GAP
in size range
8
What makes it impossible to escape from Black
Holes?
? The function of Black Holes bending
Space-Time
? What is Space-Time?
9
What makes it impossible to escape from Black
Holes? (continued)
? The General Relativity Theory and Black Holes
? Non-mathematical explanation?
10
Major features of non-rotating black holes

• Event horizon it is the defining feature of the
  black hole it is black because no light or
  other radiation can escape from inside.
  Gravitational field from outside is as any other
  symmetric object of the same mass.

11

• Singularity according to general relativity
  theory, a black holes mass is entirely
  compressed into a region with zero volume, which
  means that its density and gravitational pull are
  infinite, and so is the curvature of space-time
  which it causes.
• Singularity in a non-rotating black hole is a
  point, with zero length, width and height.
• Photon sphere it is a spherical boundary of
  zero thickness such that photons approaching
  along tangents to the sphere will become trapped
  in a circular orbit. No photon is likely to stay
  in this orbit.
• Accretion disk the gas near the black hole is
  pulled and form disk with high density. As
  result, the disk glows very brightly, although
  these disks mainly radiate X-rays, rather than
  visible light.

12
Rotating Black Holes

• Shares many features of non-rotating. Because of
  the rapid rotation of a large mass produces
  further distortions of space and time.
• It has two horizons, two photon spheres.
• Ergosphere ultra-dense rotating mass creates an
  effect of frame-dragging, so that space and time
  is dragged round it in the direction of the
  rotation. The dragged speed is faster than that
  of light.
• Ring-shaped singularity

13
(No Transcript)
14
Possibility to escape

• The properties of space and time between the two
  event horizons allow objects to move toward the
  singularity
• But within the inner horizon allow objects o move
  away the singularity, pass through set of inner
  and outer event horizons, and emerge out of the
  BH into another part of the universe. According
  to Kerrs solution for general relativity!!!

15
What happens if something fall in the black hole?

• An object in any gravity is stretched
• Experience an slowing down of time, before reach
  the horizon. Near the horizon time dilation
  increases rapidly
• Reaches the singularity within infinite amount of
  proper time
• When hits singularity object is torn into its
  components, into atoms, atoms into electrons,
  protons, neutrons. P,N,el. into quarks

16
Formation

• Stellar-mass black holes are formed in two ways
• A. As a direct result of gravitation collapse
  of a star
• B. By collisions between neutrino stars. Very
  rare.

Larger BH are formed as result of absorbing mass
or whole star clusters might merge into single
body. Smaller BH are formed by evaporation of big
one during Big Bang or by very powerful particle
accelerators. Hawking theory sea of energy
pairs of particles matter and antimatter, E into
mass. Two particles created fall into the BH one
escapes, therefore BH emits and lost a minute
amount of its mass.
17
Techniques for finding Black Holes

• X-rays and Accretion disks around black holes.
• - Maximum mass when nothing can beat gravity.
• - Black holes have no material surface, so the
  absence of irregular flares round a massive,
  ultra-dense object suggests that there is a good
  chance of finding a black hole.
• 2. The Discovery of the First Black Hole in the
  Universe.
• - Cygnus X-1, star HDE226868, luminosity
  variations, object few kilometers wide.

18
Techniques for finding Black Holes

• 2. The Discovery of the First Black Hole in the
  Universe.
• - Cygnus X-1, star HDE226868, luminosity
  variations, object few kilometers wide.
• 3. Schwarzschild radius if a body is smaller
  than its Schwarzschild radius, it is probaby a
  black hole.
• - What is a Schwarzschild radius?

19
Objects thought to be Black Holes

• 1. Super massive black holes at the centers of
  galaxies.
• - Milky Way Saggitarius A (2.6M (2.6 million)
  solar masses and has a radius of less than 17
  light hours)
• 2. Intermediate-mass black holes in globular
  clusters.
• - The Globular Clusters M19 and G1.
• - Super massive black holes grow by absorbing
  nearby smaller black holes and stars.
• 3. Stellar-mass black holes in the Milky Way
• 4. Micro black holes

20
History of the black hole concept

• Newtonian theories (before Einstein)
• - Escape velocity
• 2. Theories based on Einstein's general
  relativity

21
Black holes and Earth

• Black holes are sometimes listed among the most
  serious potential threats to Earth and humanity,
  on the grounds that
• A naturally-produced black hole could pass
  through our Solar System.
• A large particle accelerator might produce a
  micro black hole, and if this escaped it could
  gradually eat the whole of the Earth.

22
Black holes and Earth

• Black hole wandering through our solar system
• Micro black hole escaping from particle
  accelerator

23
Alternative models

• In March 2005, physicist George Chapline at the
  Lawrence Livermore National Laboratory in
  California proposed that black holes do not
  exist, and that objects currently thought to be
  black holes are actually dark-energy stars. He
  draws this conclusion from some quantum
  mechanical analyses. Although his proposal
  currently has little support in the physics
  community, it was widely reported by the media
• Among the alternate models are magnetospheric
  eternally collapsing objects, clusters of
  elementary particles, fermion balls,
  self-gravitating, degenerate heavy neutrinos and
  even clusters of very low mass (0.04 solar mass)
  black holes.