Transcript Astronomy for beginners - The World of Astronomy

Astronomy for beginners
Black Holes
Aashman Vyas
What are Black Holes?
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A black hole is a super dense object that has an intense
gravitational pull
There are three parts to a black hole, a singularity, event horizon
and accretion disk
The event horizon is where the force of gravity becomes so strong
that even light is pulled into the black hole (light has a speed of
299,792.458 km per second)
Although the event horizon is part of a black hole, it is not a tangible
object
The singularity is not really a tangible object either
According to the General Theory of Relativity the Singularity is a
point of infinite space time curvature
Everything that falls into a black hole by passing the event horizon,
including light, will eventually reach the singularity of a black hole
Before something reaches the singularity it is torn apart by intense
gravitational forces (even the atoms)
How do Black Holes form?
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Imagine a star which is much more massive than our sun, and which has a mass,
called the critical mass, which is large enough to cause a black hole to form. What
keeps this star from collapsing onto itself and becoming a black hole?
The answer is that there is an intense pressure caused by nuclear reactions within
the sun. When the fuel that feeds the nuclear reactions gets used up the massive star
cannot support itself anymore
It then collapses to form a black hole.
It is interesting to note that when a black hole is formed by a collapsing star it is
actually impossible to watch the final steps of the formation of the black hole from a
stationary external reference frame
An external reference frame is a place where one watches the formation of the black
hole from far away, like an astronomer on Earth. In addition, it is impossible to see
any object fall into a black hole
This is not to say that everything appears to freeze just before entering a black hole.
As an object falls into a black hole it gets increasingly dimmer and dimmer from the
point of view of an outside observer. By the time an object gets to the edge of a black
hole, it will be completely black. This effect, called a gravitational redshift, is caused
by the immense gravity near the outside of a black hole.
Types of Black Holes
There are two types of black holes
-Stellar mass black holes
-Supermassive black holes
 Stellar black holes are the black holes
formed by stars that collapse
 Supermassive black holes form when lots
of black holes collide or when huge stars
collapse. They are found only in the center
of galaxies
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Formation of Stellar Mass Black
Holes
-Star goes supernova (see stars
presentation)
-Too much element build up
-shrinking effect (see stars presentation)
-Core shrinks and crushes atoms
-Creating a black hole
-Supernova remnant will be it’s first snack
Formation of Supermassive Black
Hole
Scenario1
-Lots of stellar black holes collide producing
disturbance due to colliding event horizons
-A few million years later they all become
one black hole
-resulting black hole is huge
Formation of Supermassive Black
Hole
Scenario2
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When the universe was young, stars were
sometimes as big as a solar system
So you can image what would happen if a star
as big as the solar system exploded and how
long the life of that star would be…(see my stars
presentation)
You can also imagine what would happen if a
star that size turned into a black hole…
These black holes could also have played a part
in the formation of galaxies
Cool facts
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First of all, if you get close enough to a black hole you will see the
back of your own head! This effect, called an Einstein ring, is caused
by the intense gravity around a black hole. When you are near a
black hole at certain distances the light that leaves from the back of
your head will travel though space that is bent so much by gravity
that it will enter your eyes
Another cool thing about black holes is that they might be able to
destroy information. The destruction of information is not allowed by
quantum mechanics, so Hawking concludes that the usual rules of
Quantum Mechanics cannot apply for black holes!!
Black Holes do not last forever. In Stephen Hawking’s theory about
Black Holes, it says that black holes radiate mass in the form of
energy/radiation. (E=mc2) So a black hole would radiate away all it’s
mass in about…lets see….about a trillion years
Bibliography
An introduction to black holes by David
Ando
 Ask an astronomer for kids
 Astronomy.com
 The big book of stars and planets by
Robin Kerrod
 The elegant universe (TV show) discovery
science
 Google images
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Thank You For
Watching!!!!