This document provides information about black holes, including their structure, theories about their formation and properties, and how they are detected. It discusses that a black hole has a singularity at its center with infinite density, is surrounded by an event horizon beyond which nothing can escape, and may be accompanied by an accretion disk and jets. It also describes Sagittarius A*, the supermassive black hole at the center of the Milky Way, and Cygnus X-1, the first identified black hole.

1. BLACK
HOLES Raúl Díaz Gómez
Daniel Hirsch Marina
Carlos Ruiz Aquino
4º ESO A

2. Definition
A black hole is a region of spacetime whose gravitational
fields are too strong for light and any mass known to
escape.
Black holes don’t emit electromagnetic radiation
(photons) but the objects they absorb do, thats why we
can see are shiny.

3. Structure of Black Holes
• The Singularity: This is the region of the black hole where all the mass of
the black hole has been compressed down to nearly zero volume. As a
result the singularity has almost infinite density and creates an enormous
gravitational force.
• The Event Horizon: This is the "point of no return". Any object, even light,
that is within this radius cannot escape the gravitational pull of the black
hole
• The Schwarzschild Radius: This is the event horizon's radius. It is the
radius at which the escape velocity is equal to the speed of light,
R = 2GM/c2

4. Structure of Black Holes
• The Accretion Disk: This is a disk
composed of stellar material that
is spiraling towards that black hole
• The Ergosphere: If the black hole
is rotating, then as it spins, its
mass causes the space time
around the black hole to rotate as
well. This region is called the
ergosphere.
• Jets of Gas: For some black holes
high intensity magnetic fields are
emitted perpendicular to
the accretion disk. This causes
charged particles to circle these
magnetic field lines and creates
jets of gas perpendicular to the
acceleration disk.

5. Theories
Most things known about black holes are only theories
that usually are not true:
• The Einstein-Rosen Bridge Theory-> it says that if a
human goes through a black hole, he will be suck
down in a tunnel and shot out in a “white hole” in a
parallel universe.
• Collapsed stars-> it says that black holes is simply a
massive, dead star whose gravity is so intense that
even light cannot escape.

6. •Russian Dolls Universe Theory-> It says that the Universe is an
infinite dark void with infinite number of planets, stars, galaxies
and intergalactic spaces floating inside and governed by the
same physical laws and constants. Like part of a cosmic Russian
doll, our universe may be nested inside a black hole that is itself
part of a larger universe.
•How black holes are created-> A common type of black hole is
produced by certain dying stars. A star with a mass greater than
about 20 times the mass of our Sun may produce a black hole at
the end of its life. But most of the stars cannot become a black
hole because they don’t have the mass to become it so when
they die, they become white dwarf star which will sink due to its
own weight.

7. How to detect Black Holes
The black holes don’t emit electromagnetic radiaton (photons) so it’s
quite difficult to detect their effects. His gravitatory effects can be
noticed in near objects which movement is influenced by the black
holes.
As they don’t emmit light they are impossible to see but the objects
they absorb do so thats why black holes can be seen.
They also are detected through the gravitational lens effect which
refers to the distance between the and an observer, that it is capable to the
light from the source, as it travels through the observer. This effect is known
as gravitational lensing and is one of the predictions of Albert Einstein's
general theory of relativity.

8. Sagitario A
It is the closest black hole to the Earth. Astronomers are confident that
these observations of Sagittarius A* provide good evidence that our own
Milky Way galaxy has a supermassive black hole at its center.
In Chile, they show how the cloud is so hot that her front has already
passed the point of maximum approach and away from the black hole of
more than ten million miles per hour, while the tail is still falling towards
him.

9. Sagitario A
Location
It is located at the center of the
Milky Way.
Discovery
It was discovered on February 13th
1974 by the astronomers Bruce
Ballick and Robert Brown using
the interferometer of the National
Radio Astronomy Observatory.

10. Cygnus X-1
It is a well-known galactic X-ray source and black hole candidate in
the constellation Cygnus galaxy. Cygnus X-1 was the first and brightest source
of x-rays discovered in Cygnus galaxy due to the objects he absorbs (X-rays
are a form of electramagnetic radiation (particles of light) that carry more
energy than the light we can see). It is now estimated to have a mass about
14.8 times the mass of the Sun and has been shown that is too compact to be
any known kind of normal star or other likely object besides a black hole. If so,
the radius of its event horizon is only about 44 km.

11. Cygnus X-1
Location
It is located in the Cygnus Galaxy.
Discovery
It was discovered by the Uhuru satellite in
1791.