2. A look through Black Holes' history
In 1783, Jhon Michell conjectured that there might be an object massive
enough to have an espace velocity grater than the speed of light
Albert Einstein first predicted black holes in 1916 with his general theory
of relativity.
The term "black hole" was coined in 1967 by American astronomer John
Wheele.
The first one was discovered in 1971. It was the binary star Cygnus X-1.
Its effect on its companion star suggested that it must be a compact
object with a mass too high for it to be a neutron star.
In 1974 Stephen Hawking combined theories of General Relativity and
Quantum Mechanics to show that black holes radiate energy. Although
initially ridiculed, this is now generally accepted in the field of astro-physics.
3. But...What are they?
They are regions in
space where the
gravitational attraction
is so strong that even
light cannot get out.
They are
caused
by a very
dense
mass that
has
already
pilled up.
We can't think
of a black hole
as the usual
meaning of
“black hole”.
They aren't
totally balck and
they aren't holes
at all, instead
they are regions
where neither
light nor matter
can escape.
They don't have any grater gravitational reach than any other star of the
same mass.
4. Structure of Black Holes
● There is a region of space surrounding the black hole from where
light cannot escape. It's called the Event Horizon. It's the point
where the escape velocity from the gravitational field is equal to
the speed of light. Is the place farthest away from the middle
where the gravity is still strong enough to trap light.
● The Singularity is the gravitational center in the middle of the
black hole.
● The event horizon's radius is called the Schwarzschild Radius
● The Accretion Disk is a disk composed of stellar material that is
spiraling towards the black hole.
● The Ergosphere is the cape surrounding the black hole. If the
black hole is rotating, then as it spins, its mass causes the space
time around the black hole to rotate as well.
● 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. T
Y
P
E
S
O
F
B
L
A
C
K
H
O
L
E
S
Supermassive black holes: they are the largest ones. Their masses are
more than 1 million suns together. In every large galaxy there is a
supermassive black hole in its center. The supermassive black hole in the
centre of the Milky Way is called Sagittarius A. Its mass is equal to 4
million suns together.
Stellar black holes: they are the most common black holes. They have a
mass that can be 20 times more than the mass of the sun. In the Milky
Way there are many of them.
● Micro black holes: their masses are as small as 20 micrograms. They
exist in theory, but have no directly detected. It is thought that they are
all around our atmosphere.
6. Formation of Black Holes
Stellar black holes are made when the center of a very big star falls
in upon itself or collapses and this causes a supernova, leaving a
black hole core behind where the star once exist.
7. Supermassive black holes are the result from the merger of stellar
black holes and other matter, from the collapse of a extremely high
mass star. They were formed when the Universe was still very
young.
Micro black holes would be created during the collision of two very
high energy particles.
8. How can we see Black Holes?
Scientists can't see black holes. They are invisible because no light can
get out.
With special tools they can see where black holes are located in three
different ways:
Surroundings: They can see how stars that are very close to black
holes act differently than other stars. The light emitted by them will
appear distorted or the stars will appear to move in an unusual way.
Gravitational effect on planets, comets and asteroids.
With the Hawking Radiation: Stephen Hawkings says that energy
escape from a black hole. Matter will be created in the form of an
electron and anti-electron. When it happens near the event horizon, the
positive particle is ejected away from the black hole and the negative
particle falls into the black hole. Therefore, black holes lose more mass
than they gain.
9. Recent Discoveries
2013/2014
*Astronomers have discovered a black hole that is consuming gas from a nearby
star 10 times faster than previously thought possible. The black hole lies about 12
million light years from Earth and is ingesting a weight equivalent to 100 billion hot
dogs every minute.
*Astronomers working with NASA have found a pulsating dead star beaming with
the energy of about 10 million suns. The object, previously thought to be a black
hole because it is so powerful, is in fact a pulsar - the incredibly dense rotating
remains of a star.
*There is an ultra-compact dwarf (little) galaxy located about 55 million light-years
from Earth in the Virgo cluster. Despite its diminutive stance, the galaxy appears to
harbor a supermassive black hole.
*New evidence has been uncovered for the presence of a jet of high-energy
particles blasting out of the Milky Way's supermassive black hole. Astronomers
have made the best case ever that a jet exists by combining X-ray data from
NASA's Chandra X-ray Observatory with radio emission from the NSF's Very
Large Array (VLA).
10. Could the Ear th be destroyed by Black Hole?
No Black Hole is
close enough to the
solar system for Earth
to be destroyed by it.
If a Black Hole of the same mass took the place of the sun, Earth
wouldn't fall in, because the Black hole would have the same gravity as
the sun and our planet would orbit the Black Hole, as would the rest of
planets.
Other things would be affected, such as the amount of light.
11. Stephen Hawkings talks
about Black Holes
In the “Festival Starmus” in Tenerife, Stephen Hawkings said that there is
an exit in black holes. Particles can get out of them by returning outside
or arriving to another universe.
He also said that if a particle falls into a black hole, its partner can follow
it or not. In the second case, this is what origins the radiation emitted
from black holes, called Hawking Radiation as we talked about. He
added that when the anti-particle falls into a black hole is possible that it
is travelling to the past and that it can lose information.
12. Here there is a video of
Black Holes
http://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html
